Wednesday, October 04, 2017

Birds on Radar, October 3rd, 2017

At whatever moment you read these words, day or night, there are birds aloft in the skies of the Western Hemisphere, migrating. If it is spring or fall, the great pivot points of the year, then the continents are swarming with billions of traveling birds...
- Living on the Wind: Across the Hemisphere with Migratory Birds

After three nights and days of rain, storms, and winds from the south, last night was finally clear and calm. The full moon was so bright that no light was required as I walked up and down my driveway and around our yard. While I couldn't see any birds, a few short flight calls overhead told me that a great river of birds was flowing in the sky above me.

Bald eagles and other bird of prey migrate during the day, when they can take advantage of thermal soaring to help lift and carry their large bodies long distances. But many songbirds migrate in large flocks or swarms at night. Avian predators are less active, skies are often less turbulent, the cooler night air is slightly denser and helps birds dump heat and like sailors, birds can use the stars for navigation across an otherwise relatively featureless landscape.

How many birds were migrating last night? Two words: Green Doughnuts.

The map above shows reflectivity, defined as the amount of transmitted power returned to the radar receiver after hitting precipitation, compared to a reference power density at a distance of 1 meter from the radar antenna. In short, when radar hits stuff, it gets bounced back. The more radar that gets bounced back relative to the reference, the more intense or denser the stuff it is hitting: precipitation, flocks of birds, migrating bats, insects rising into the sky, and so on.

If you look at the map above, you can see a line of storms moving to the east. Some of these storms are dropping quite a bit of precipitation, as shown by the yellow and red colors in Michigan's Upper Peninsula. But you can also see blue and green doughnuts or blooms blowing up around sunset (which occurred at 6:47pm CT in eastern Minnesota and Iowa last night). The unique pattern, lower reflectivity, behavior (an ebb and flow that begins at sunset and begins to peter out at about 1:30am), weather, and time of year all tell us that these are migratory birds.

So why was I excited about green doughnuts? Check out the reflectivity key below...

The colors represent the strength of returned energy to the radar expressed in values of decibels (dBZ). As we stated earlier, the amount of radar reflected back to the ground unit is proportional to the number and diameter of stuff - drops/flakes/birds/insects - per unit volume. The US Weather service defines rainfall rates and types here, while the Cornell Lab of Ornithology defines bird 'rates' (but not types) as follows:

  • Minimal migration: < 5 dBZ — fewer than 59 birds per cubic kilometer
  • Light migration: 5-10 dBZ — approximating 59-71 birds per cubic kilometer
  • Moderate migration: 10-20 dBZ — approximating 71-227 birds per cubic kilometer
  • Heavy migration: 20-30 dBZ — approximating 227-1788 birds per cubic kilometer
  • Extreme: >30 dBZ — more than 1788 birds per cubic kilometer (actually  occurs at some times in very rare circumstances)

Blue doughnuts are pretty typical, at least during the summer months. But green doughnuts are something else! Last night's radar shows heavy migration that approached extreme migration in some places. As I walked and listened, I thought it was probably a pretty special night. I can't believe how special it really was! I'll be out looking and listening for birds again tonight.

Additional Resources
How do normally diurnal birds become temporarily nocturnal? Read more about that here (warning - this is a dense read):

The Cornell Lab of Ornithology publishes bird forecasts and migration reports on their website at Check it out and keep those feeders filled for hungry seed, nut, and suet eaters that are resting and refueling in your yard!

BirdNote did an excellent story about nocturnal migration. You can listen to that here:

The Old Bird studies nocturnal flight call activity. While he isn't the only one, almost everyone involved in this activity cited him as the original. Check out his website at:

Thanks to the University of Wisconsin, we have a national radar map here: and one showing migration for the great lakes/upper midwest here: These maps archive data over several months. We encourage you to check them out and compare nights - summer versus winter, stormy nights versus calm nights, and good flight nights.

Good luck birds, and we'll see you next spring!

Friday, September 08, 2017

What's on the menu at Fort St. Vrain? An exploration of nest remains, part I

So what's on the menu at Fort St. Vrain? While we were up in the nest, I decided to collect prey remains. We don't have the necessary permits to take feathers (of which I found only two, both belonging to prey), but there were plenty of skulls and a few turtle shells. I got them home, laid them out on a table, and started ID'ing them. Some Moms bring home t-shirts and postcards. I bring home skulls and photos of prey.

The photo below shows all of the remains I recovered from the nest, along with the book that Elizabeth Ries and I used to identify them. In all, we found 35 fish remains (skulls, skull fragments, opercular bones, jawbones, and an otolith), seven prairie dog skulls and one foot, one desert cottontail skull, one common muskrat skull, three western painted turtle shells, and some unknown vertebrae. Even in a relatively dry environment, the eagles show a clear preference for fish. As you can see from the opercular bones and skulls, some of the fish were pretty large!

From bottom to top: six right opercular bones, six fish skulls and skull fragments, 11 left opercular bones and one otolith, seven fish jawbones, three western painted turtle shells, vertebrae, four unknown skulls, seven prairie dog skulls, one muskrat skull, one desert cottontail skull
This blog will deal with mammal remains! To make the job easier, I started by assuming that most of the mammalian skulls were probably prairie dogs given the close proximity of a prairie dog colony to the nest. We divided them into groups of skulls that looked alike (which of these things is not like the other?) and got the skull book out!
Top to bottom: desert cottontail, muskrat, black-footed prairie dog
Take a look at the skulls above. The top skull is quite a bit different than the other two, with a high, rounded top and a slightly different eye socket and muzzle (although much of the muzzle was gone). The bottom two skulls are flatter, 'boxier', and have different suture patterns. I decided to start with the bottom skull, since we had seven of them and just one each of the other two. Sure enough, Animal Skulls, A Guide to North American Species verified that we had a black footed prairie dog! Our skull had well developed post-orbital processes (the bone spurs jutting out almost perpendicular from the skull over the eye sockets), v-shaped temporal ridges (the 'V' on the skull), well-developed occipital crests (the ridge at the back of the skull), and (not real visible in this photo) broad nasals with squared posterior edges. It was a prairie dog! But what were the other two?

I started by thinking about the animals I had seen around the nest. How about a rabbit? Elizabeth and I began with looking at what kind of rabbits lived in the area. After a lot of comparison, we settled on a desert cottontail. The skull has a relatively round, large braincase, the eye sockets are similar, with a posterior extension that is "long, broad, and often fused to the braincase" (this helped us rule out brush rabbit), and a broad and high intraorbital region, or top of the skull.

Elizabeth suggested we take a look at the ventral, or underside, of the skull. Good idea!
Desert cottontail, ventral view
This turned out to be very helpful! She observed that the teeth lined up exactly with the desert cottontail's teeth, the heart-shaped structure at the top of its mouth formed by the palatal bridge begins near the anterior of the second cheek tooth and terminates just into the fourth tooth, the incisive foramina are large, and the skull has a medium forum magnum that resembles the one pictured in Skulls. Unfortunately, we didn't have a mandible to compare, but I feel pretty comfortable calling this a desert cottontail.

Since the ventral view was so helpful in identifying mystery skull #2, we decided to start with the underside in skull #3. Wow - look at those distinctive teeth! This should be easy!
Ventral view
The teeth were distinctive, but not as much as we hoped. We eventually ruled out northern pocket gophers. Like this skull, they have smooth incisors, but the skull shape was all wrong. We went on to rule out other types of pocket gophers and eventually just ended up looking for teeth that matched the skull as I racked my brain to think about what else could be out there. And then we found the muskrat skull. VoilĂ !
It was a muskrat, not a pocket gopher!
Muskrats are semi-aquatic rodents found all over the United States, including Colorado. The skull has orange, smooth mandibles, the anterior edge of the squamosal has a strong angular projection (look at the squared off ridges protruding over the eyesockets), giving the braincase a 'squared' appearance, and its temporal ridges are developed (look at the back of the skull). The teeth descend in size to the posterior, the first lower molar has five closed triangles or loops, and the incisive foramina (aka the long slits visible in the roof of its mouth in the ventral view) are long and thin, with the posterior edges aligned with the anterior edges of the toothrows.

Elizabeth and I found the skulls quite fascinating. We discussed the distinctive teeth of the muskrat, which is the only mammal of the three to eat underwater. Its short tooth 'plate' allows it to grind tough fibers behind closed lips, which keeps water from running down its throat. We noted the high, rounded skull and facial tilt of the rabbit skull, which may help it to leap and bound - something neither prairie dogs nor muskrats do - by keeping its nose down and out from its line of sight. And we talked about the high post-orbital processes of the prairie dog, which also occur in some squirrels and marmots. These bony barbs help anchor ligaments, pulleys, and other connective tissue, but why do prairie dogs have them when muskrats don't? Were they inherited from a distant ancestor, or do they reflect a more recent evolutionary development. Even though the animals were long gone, their skulls told us a lot about the way they had lived.

We'll look at fish and turtles in the next blog!

Why so many prairie dogs versus other mammals? There is an active colony very close to the nest, just below some large power poles with great cross braces. The eagles can perch right above the colony and wait for an unwary prairie dog to get a little too far from its hole. Prairie dogs are also relatively large and meaty - a nice size dinner for the amount of energy expended catching it!

Interested in ID'ing the skulls of North American animals? Check out Animal Skulls, a Guide to North American Species, by Mark Elbroch. We would not have been able to make ID's without it! 

Did you know that prairie dogs are believed to have a rudimentary language? Given Ma and Pa's presence, I assume they have a call for 'eagle': 

Live from the Fort St. Vrain Bald Eagle nest!

Back in late August, John and I traveled to Platteville, Colorado, to work with Xcel Energy employees Bill Heston, Tina Lopez, and Naresh Dahagama on an upgrade to the Fort St. Vrain Eagle cam. Over three days, we took down and re-positioned the existing cam, added a new PTZ cam, cleaned up the solar panel area, added two radios and a couple of networked video recorders so plant staff could watch their eagles from the lunchroom again, threw in a couple of network switches to tie everything together, and got an IP camera configured for the Fort St. Vrain owl nest. One of the eagle cameras is currently up here: and we hope to have both available soon! We did the best we could to position all of the cameras out of poop range!

So what does the area look like? The Fort St. Vrain bald eagles are nesting in a large cottonwood near the junction of the St. Vrain and Platte rivers. A variety of animals drink at the waterhole just below their nest, western painted turtles sun themselves on logs, fish swim in both rivers, and prairie dogs squeal and dig at a large colony roughly 1,000 feet away. Their grove is populated by cottonwood trees with an abundance of perches, which provide great places to sun and shade while searching for potential prey. Like many grassland groves, it is located on the east or leeward side of a river, which serves as a natural firebreak against fires driven by western winds. While life is not always easy here, the eagles' grove is a small oasis in the dry landscape around them.

A look at the nest area. The plant is about 1/2 mile from the nest.
The nest itself measures eight feet, one inch by six feet, seven inches by nine feet, ten inches. The total area is a bit tough to calculate since it sits somewhere between a triangle and an oval, but if I calculate for both and average them, I come up with around 30 square feet. It is about 6.5 feet high, constructed almost entirely out of cottonwood sticks - far and away the dominant tree here - and contains at least three other bird nests. It has excellent flyways - perhaps due in part to stick-snapping and nest-building activities - and favorite perches as indicated by well-worn spots on branches right next to the nest.

A look at the nest! 
What does the nest weigh? Using the method outlined here for calculating a cone - the closest shape I could come up with - yielded a total volume of 103 cubic feet (note that I calculated the radius by averaging the three measurements I had). Cottonwood weighs about 28 pounds per cubic foot, which yields a weight of 2,884 pounds...if the nest were constructed of solid wood. But it isn't, since the eagles weave branches together in a rough spiral. Once the solid weight is multiplied by the fibonacci ratio of 61.8%, we get an estimated weight of around 1,700 pounds. 61.8%, which is also referred to as the golden ratio, or the golden mean, turns up quite a bit in natural series, especially ones that involve spirals. Don't believe it? Check this out: The Golden Ratio In Nature. The Fort St. Vrain nest is larger but, thanks to its cottonwood construction, probably lighter than N2B in Decorah.

Bill Heston. He worked with Bob and Joe on the original Fort St. Vrain camera system.
I knew that the Fort St. Vrain folks liked their eagles, but I really didn't understand how dedicated they were until we got out there. Bill Heston spoiled us with his expert lift operation - it was like riding an elevator to the nest! - and everyone was thrilled to be able to watch the eagles in the lunchroom once again. A thousand thanks to the Xcel Energy team for all of their great help and support! I'd like to come back and bioblitz your land...maybe next year? In addition to a juvenile bald eagle (we did not see either adult), we saw a great blue heron, a flock of wild turkeys, a belted kingfisher, red-tailed hawks, a woodpecker of some sort (it wasn't close enough to ID) prairie dogs, and a rabbit.
Tina Lopez getting ready for the lift!
While we were up in the nest, I decided to collect prey remains. We don't posses the necessary permits to take feathers (of which I found only two, both belonging to prey), but there were plenty of skulls and a few turtle shells. I got them home, laid them out on a table, and started ID'ing them. You can read all about that in our next blog!

John Howe in the nest!

Tuesday, August 08, 2017

Persistence Pays Off – a post by Brett Mandernack about the fitting of D27’s transmitter.

Fitting D27's Transmitter
It is early August and I have one satellite transmitter (or PTT) yet to deploy on a young eagle. Dave and Ann Lynch spent two solid weeks in late June/early July perfecting their craft of artful presentation of fish to the Decorah fledglings, yet the “kids” instead chose to food-beg loud and often and insist Mom or Dad bring them food at the nest. There was no evidence of any of the fledglings ever picking up a fish during that time. In previous years we’ve had multiple fledglings coming to the same spot – the mulch pile – for some easy meals, and usually within just a few days of watching and waiting for our talented trout tossers to appear.

When visitor attendance diminished at the hatchery in late July, all three fledglings were still being spotted with regularity by several of our sharp-eyed eagle watchers. Hatchery biologist Brian Malaise and I kept in touch often and he and his crew again put fish out in the same spot. Lo and behold, the female, D27, began showing interest and eventually took advantage of these easy meals each morning. One of the males was believed to have also helped himself to the free offerings.

We chose Monday, August 7 to attempt to capture whichever youngster decided to come to bait. My wife Carole, Eagle Valley Technician Ryan Schmitz, and I arrived at Willard Holthaus’s shop by 5:15 AM and quickly set the padam noose trap baited with three nice hatchery trout. Weather was perfect: 58 degrees, mostly clear sky, light wind. All equipment and supplies were laid out in the shop in anticipation of a successful capture. Then we watched and waited. A few adult calls were heard from near the nest tree by 6:05. Then at 6:15 an immature eagle appeared from the west just above treetop height. I speculated it was large enough to be female D27. She landed in the maple tree briefly, then headed toward the mulch pile, looped over that area, perhaps checking out what food might be there, then circled back and landed on the mulch pile. We had placed a small trout atop the mulch pile, which she decided looked like a great appetizer. She rather daintily ate the fish and began eying the three trout just two feet away. She walked inside the padam, grabbed a fish or two in a foot, and tugged at them a few times as we all watched intently. When I was convinced she had a noose around a toe or foot, I gave the call to “GO, GO” and Ryan and Brian sprinted ahead to secure her. She was captured at 6:18, hooded, and taken to the shop where she was weighed (9.48 #) and had several measurements taken. The composite of those measurements revealed she is a small female. The entire process of getting measurements, banding, and fitting of the PTT was fluid and seamless.

Within an hour of capture we were ready to release D27 and begin what is likely the final chapter of the Decorah eagle tracking story that began with our beloved D1 back in 2011. After placing her back on the mulch pile, she quickly oriented herself and flew north alongside the N1 Cottonwood tree to settle along Trout Creek.

I cannot imagine a better crew than Carole and Ryan. John Howe, Brian, and friend Andrew Batt documented the entire process with photos and video. And a huge “Thank you!” to Willard for again making his shop available for all of this. What a great example of teamwork by all. I am so thankful for everyone’s input, time, and patience.

After tracking primarily adult eagles since winter 1998-99 to determine migration dynamics in the Upper Midwest, their fidelity to migration routes, as well as fidelity to and mobility on summer and winter ranges, The Eagle Valley Nature Preserve study has recently been focusing on immature eagle travels and observing if/how the migration behavior changes as the birds mature. The Decorah eagles have provided an outstanding opportunity to track eagles of known origin from this region and begin to answer the oft-asked question of “where do the Decorah eagles go when they leave Decorah?”

We encourage all of you to join us in our prayers and positive believing that D27 lives a long, healthy life and the PTT functions properly for several years so we can continue to reveal the intricacies of eagle migration behavior.

Stay tuned: thanks to Brett and crew, we will share D27's travels at

Thursday, August 03, 2017

What's On The Menu at Decorah North Nest? A guest blog by Sherri Elliott

Dad brings in the two-for-one suckerfish special!
It's been a bountiful season for The North's in the quantity of prey hauled home and caught on camera.  A total of 449 meals delivered this year vs 163 meals in all of the last season.

32 meals were enjoyed just by Mr and Mrs North during nestorations and before the first egg was laid,  409 meals delivered to the nest from first egg laid to fledge, and another 8 "picnics in the pasture" post fledge dropped to the fledglings.  That's quite a bounty!  Also noteworthy is the true partnership in procuring the provisions by the parents to provide for their peeps.  Last year it seemed that Mrs. North was more proficient than Mr. North in fishing, hunting, parceling out, or pilfering protein but this year the tally was almost 50/50 with Mrs. North bringing in 231 meals and Mr. North delivering 210 meals to the nest.  The North's seem to practice 'field dressing' prey by breaking down larger animals and bringing in pieces or sections of their protein, but each delivery was counted as a meal. It's almost impossible to determine via long distance food drops the division of duty for the picnic meals, so those 8 meals are tallied as unidentified protein brought by an unidentified parent.

The earlier egg lay this season (more in line with hatchery Decorah Eagles) allowed Mr. and Mrs. North to take advantage of the abundant fish runs of trout and suckers as well as filleted discards from the friendly landowners, more than doubling their haul to 246 fish this year vs 109 fish last year. Special applause to Mr. North on 4-12 for his 2 sucker fish delivery in a one-foot talon hold; and the new record on 5-13 of 9 fish in one day with 8 caught by Mr and 1 from Mrs. North.   Other notable deliveries were 4 fawn heads, and other assorted deliveries of deer legs and quarters;  Mrs. North's preference for 'cowghetti' (stringy cow placenta); and 2 turtles.

What we learned this year is what excellent providers the parents are in purveying provisions for the pantree, and while not a lot is stockpiled like we see at the hatchery nest to the south, the remains are picked clean and dutifully taken to the dump when done.  Both parents took an active role in feeding their offspring and there were several instances where Mr. North would have taken more of a share in feeding if not for Mrs. North's teakettle that she'd be in charge. This may have happened last year but the new microphone at the nest amplified the vocals that we have come to know as common by Mom Decorah, and it was interesting to add to our observations.

Here's the full list of menu items in whole or part.
  • Feathered: Birds (6), Chicken and parts (4), Coot (2), Duck (1), Gosling (2), Grouse or Pheasant (3), Turkey or Goose (1).
  • Fins: Trout (144), Sucker (44) Fish pieces (58)
  • Fur: Deer - Heads (4) and Legs or sections (12), Groundhog or Muskrat (2), Opossum (2), Rabbit (8), Raccoon and pieces (11), Squirrel (6) 
  • Reptiles: Turtles (2)
  • Rodents:  Field Mice or Voles (4)
  • Misc: Cow Placenta (37), Mystery Meat or Unidentified Food Objects (48), Animal legs/feet (4), Pink/Red Innards (24), Bony Meat (12)

Tuesday, May 30, 2017

More on Great Spirit Bluff

We are getting a lot of questions about the perch design at Great Spirit Bluff. Are falcons jumping because the perches are poorly designed? No - they are jumping because of an unusually early and intense (what we call explosive) - emergence of adult black flies.

Why are we so sure? The sites at which we have platforms (Xcel Energy's Allen S. King and Sherco plants, for example) don't have better production records than the sites at which we don't (every cliff site, sill-mounted sites at power plants, and stackhouse sites, to name a few).  Great Spirit Bluff didn't begin having problems until our first black fly hatch in 2013. As you can see below, the only exception was 2008, and I suspect we had a new female (probably Michelle's first year) because the nest chronology really went very late, shifted early the next year, and stayed early. We installed the nest box here in 2003, falcons adopted it in 2005, and we put it online in 2011. Here is what the record looks like. You can check it for yourself at

  • 2005 - 4 falcons produced
  • 2006 - 3 falcons produced
  • 2007 - 3 falcons produced
  • 2008 - 1 falcon produced
  • 2009 - 4 falcons produced
  • 2010 - 4 falcons produced 
  • 2011 - 4 falcons produced
  • 2012 - 3 falcons produced
  • In 2013, we banded four young. All of them stampeded from the nest following a blackfly swarm. We recovered one from the ground below the cliff and transplanted him to a nestbox with two young of the same age. He survived and fledged just fine. Two other falcons must have survived and been fed by the parents, because they showed up at the nestbox one day, all feathered out and looking great. One probably died - we never saw it again and it hasn't turned up anywhere else yet.
  • In 2014, only one egg hatched. Watchers might remember that as a really brutal spring. We banded the lone male, but he stampeded from the nest box at about 30 days of age following a black fly swarm. We found him below the bluff with our cameras and monitored him as his parents cared for him. He fledged just fine. 
  • 2015 - 4 falcons produced
  • 2016 - 4 falcons produced
  • In 2017, two young falcons died following a black fly swarm. We recovered both carcasses, did a field examination on one (referencing 'Managing Peregrine falcon at the Eyrie' by Cade), and took the other into the U of MN for an autopsy. We are still waiting for the results from U MN. The one we examined had multiple bites along the edges of both wings, its wingpits,  the skin around its eyes, and its cere, It had a couple of bites (but not many) in its thighpits. There were no bites or sign of insects in its mouth, its nares, or its nasal passages. I did a field examination on the two survivors when we banded Sunday, and neither one of them were nearly as badly.
A couple of comments on 2017 - the swarm was earlier than we have ever seen it and we have never at ANY of our cammed sites seen young falcons venturing outside at roughly 17 days of age. Not on platforms. Not on bars. Not ever, not anywhere.

We are researching ways to design a box that will minimize black fly swarming and offer a slightly larger platform, but if this is a problem with the falcons we watch, it is also a problem for countless birds we can't see. It is time to start thinking about ways that climate change is impacting the birds we watch and love and the birds we love but can't see. If we don't recognize the problem or confine the problem only to what we can see, we can't make a difference.

So why do we think the falcons died? We are still waiting for autopsy results, but black flies are a vector for blood parasites that kill young birds with undeveloped immune systems. A link: Whether or not you understand that climate change is linked to anthropomorphic activity, use your favorite search tool to learn about climate change, black flies, and mosquitoes, just to name a few. 

Tuesday, May 23, 2017

Black flies and falcon deaths at GSB

As watchers of Great Spirit Bluff know, we lost two falcons to what we suspect are a species of black fly/buffalo gnat. At this point, we believe that flies clogged the airways of the young falcons, suffocating them. We plan to collect the carcasses on May 24 for examination. Although none of us believe that the flies came from within the box, we'll take a sample of gravel for examination as well.

We've had black fly problems here in the past. In 2013 and 2014, young falcons were stampeded from the box in mid-June, when they were roughly 30 days of age. But that we know, we've never had a serious problem this early. Why are black flies swarming the box now? It is a more complicated answer than you might think.

Which black fly is this? There are 30 species of black flies in Minnesota, but not all of them are good candidates for this location. For example, it probably isn't Simulium johannseni (develops primarily in the Crow River) or Simulium meridionale (develops primarily in the Minnesota and Crow rivers), but ruling out those two still leaves 28 possibilities. Although black flies as a whole are grouped into one family (Simuliidae), black fly species have very different life styles.  It would be helpful to know which species we are dealing with.

What does its life cycle look like? From Purdue: "The length of time it takes an egg to hatch varies greatly from species to species. Eggs of most species hatch in 4-30 days, but those of certain species may not hatch for a period of several months or longer.  The number of larval stages ranges from 4-9, with 7 being the usual number.  The duration of larval development ranges from 1-6 months, depending in part on water temperature and food supply. The life cycle stage that passes though winter is the last stage larva attached underwater to rocks, driftwood, and concrete surfaces such as dams and sides of man-made channels."  In short, the eggs for the 2017 hatch were most likely laid in 2016. The larvae emerged somewhere between one month ago or six months ago. When I compared average April temperature and precipitation for the area for every year between 2013 and 2017, I found that April 2017 was the warmest, if not by much.

Average Temp (F) Average Precip (inches)
 April 2017 53 4.87
 April 2016 50 1.08
 April 2015 51 4.16
 April 2014 45 7.03
 April 2013 43 6.11

The complicated structure of black fly life means that we also need to look at the conditions last fall and winter, which were unusually warm and dry. Did more eggs and larva stay local given the lower river current? Did more larva survive given the unusually mild conditions? Did the slightly warmer April weather lead to an earlier season? Did sun and warm temperatures following days of cold and rain lead to an explosive hatch? John noted that the swarm seemed to blow up and fade very quickly. This video shows 'those dreaded flies':

Can we control them?
We are looking into it, but we don't have an easy answer yet. We need something that doesn't volatilize since we can't descend to the box every day to spray it. It has to be strong enough to kill flies but not strong enough to harm hatchling and nestling falcons. It can't destroy the integrity of the box or let too much precipitation or wind in through the side. We are contacting the University of Minnesota's insect extension team to pick their brains and have also emailed Dr. Laura Johnson about safe possibilities. John and Susan had an intriguing idea about soaking mesh scrubbies in some known organic repellents and securing them in a safe location inside the nest box, so we may try that as well.

I wish we had more answers for everyone now. We'll do what we can and post more information when we have it.

Tuesday, May 02, 2017

A Peregrine falcon at the Decorah North Nest!

Peregrine falcon, Decorah North Nest
A sharp-eyed camera operator spotted an unbanded adult peregrine falcon at the Decorah North Nest this morning: What a surprise, especially given that there are no cliffs or large rock faces in the immediate area! As we've seen, the North nest is on a flyway of sorts. While almost all of the falcons we watch are on eggs right now, this could be a 'floater' - an unpaired adult falcon with no home territory. If we start seeing or hearing it on a regular basis, we'll need to figure out what it is doing in the area.

Although it isn't common, tree nesting has been documented in peregrine falcons in the United States as recently as 2013. The authors of the short communication Tree-Nesting by Peregrine Falcons in North America: Historical and Additional Records reviewed literature and found 33 North American records of peregrine falcons nesting in trees or snags in Alaska, Kansas, Illinois, Tennessee, Louisiana, Virginia, and British Columbia. However, their field research indicates that tree nesting could be more common than the literature suggests.

Of the 33 tree nests recorded between 1867 and 2007, nine were in tree cavities, nine were in the nests of other raptors (most commonly bald eagles), four were in bole 'platforms' created by a large tree breaking or snapping, and ten were unspecified. Of the nine nests found by the researchers between 1998 and 2013 in California and Washington state, six were in bole platforms, one was in a very large snag, and two were in bald eagle nests.

Peregrine falcons tend to imprint on nest sites, so would they be likely to cross over to trees on their own? The re-establishment of tree nesting peregrines in Europe didn't occur until fledgling peregrine falcons were tree-hacked in a process very similar to Bob's cliff release program. But peregrine falcons have taken over osprey nests with no assistance or direction in New York and New Jersey, and the breeding sites reported by Buchanan, Hamm, Salzer, Diller, and Chinnici are the first documented tree nests used by Peregrine Falcons in Washington and California, the first use of redwoods, Douglas-firs, and grand firs ever recorded, and the first reported snag use by peregrines in North America in over 60 years. As the authors state, Additional records of tree-nesting might
be expected if Peregrine Falcon populations continue to increase beyond levels already thought to have exceeded historical abundance (Ratcliffe 1993, Hayes and Buchanan 2002). Given the platform and tree nests in New York, New Jersey, California, and Washington state, it seems that peregrines can change their nesting behavior, although we don't know how likely they are to do so.

One appearance near a bald eagle nest does not make a tree-nesting peregrine population make, but a peregrine in an unexpected place is always exciting to see and we'll keep everybody posted!

A quick end note: as many of you know, Bob identified the 'bird mounds' at Effigy Mounds (and other places) as peregrine falcons in part because they were shaped like peregrine falcons and in part because they were often located near historical peregrine eyries. His research on that can be read here: When Bob was asked about falcon mounds in places with no cliffs or falcons, such as the Five Hawks effigy mounds once located near Prior Lake, Minnesota, he replied that there had probably been tree-nesting peregrine falcons in the area when the mound builders were active. While we can't know for sure, it is wonderful to think that there may have been tree nesting peregrines in Minnesota, Iowa, and Wisconsin a very long time ago. 

Wednesday, April 26, 2017

Eaglet Growth and Development: Week Four

Top to bottom:
Decorah N2B, Decorah North,
Xcel Fort St. Vrain
Most of our eaglets are in their fourth week of life: 26, 25, and 22 days old at N2B in Decorah, 27 and 26 days old at the Decorah North nest, and 31 and 29 days old at the Xcel Energy Fort St. Vrain nest. Over the past 16 days, we've seen eaglet footpads and legs growing and turning yellow, talons darkening from taupe to black, grey thermal down replacing white natal down, and pinfeathers emerging from eaglet wingtips. The eaglets have started coughing up pellets, playing 'house' (moving grasses and other nesting material around), and taking their first steps towards self-feeding ( As their vision, coordination, and strength have improved, the eaglets have expanded nest explorations and started to track events outside their nests, although they also spend a lot time sleeping off big meals and cuddling or even hiding under piles of grass in the cooler, wetter weather at both Iowa nests.

Several watchers have asked if the eaglets are going to fledge soon given their size.  No - as hard as it is to believe, we still have roughly 50 days until fledge at both Decorah nests and 45'ish days until fledge at Fort St. Vrain! Eagles grow very rapidly in their first thirty-five to forty days of life, gaining weight and building bones, muscles, tissue, and features like tarsi, footpads, toes, and claws. But during an eagle's fifth week of life (28 to 35 days), feather growth starts to overtake structural growth. Pinfeathers grow from eaglet wings, tails, and backs; beak, leg, and footpad growth all slow; and wing growth speeds up. So what can we look forward to in the coming week? Remember, the eaglets we are watching range from 22 days (D28 is just starting its fourth week) through 31 days (FSV34 is about halfway through its fifth week).
  • The eaglets should start standing on their feet. This will change nest exploration and poop-shoots. Look out below!
  • Natal down mohawks will vanish and dark deck feather growth will accelerate. Look for the eaglets' feather 'cloaks' to start filling in.
  • Still enclosed in their keratin sheaths, eaglet pinfeathers will grow longer. 
  • We may be treated to the beginning of wingercizing sessions! Once the eaglets can stand, they can really begin exploring their wings. 
By the end of their fourth week, the eaglets could be standing. By the end of their fifth week, they will be standing and could be starting to walk. I have no doubt that many of us will be mouse-clicking, shoeing, and blowing to get inquisitive eaglets back into the center of the nest as they widen their explorations and begin broadening their horizons! We will also see changes in behavior. Although the eaglets continue to compete for food, baby bonking has mostly ceased. This always makes me wonder what functions it serves. We know bonking strengthens muscles, aids coordination, and helps improve eyesight. Does food competition lead to greater food intake, helping to fuel an eaglet's rapid growth? Does it lay the ground for future social interaction, which includes plenty of body language, vocalization, and dominant/submissive interaction? Does it give parents information about an eaglet's overall heath, or help prompt provisioning? Or is it simply replaced by a new suite of physical behaviors as the eaglets begin to explore the nest and enter the next phase of nestling life? Bonking may have ended, but the eaglets are starting to play with sticks, move towards a full stand, and expand their explorations of the nest.

While we've been making guesses at gender, the weight of the two sexes begins to separate as females gain weight faster than males.  Sex takes over from age as a size determinant around 50-60 days. But cameras can be tricky and clutches can have large males and small females or be all one sex, making ID impossible without measurements or a genetic test. We'll have a lot of fun seeing if size conforms to our observations based on what we have seen of beak size, commissure extension, and other traits, and I can hardly wait for food tearing and wingercizing!

The general stages of eagle development are:

Stage 1 - Structural growth. In their first thirty-five to forty days of life, eagles grow very rapidly, gaining weight and building bones, muscles, tissue, and features like tarsi, footpads, toes, and claws. This phase of development slows down about halfway through an eaglet's time in the nest, even though individual features might continue some level of growth.

Stage 2 - Feather and flight-related growth. Eagles grow four sets of feathers - natal down inside the egg, thermal down, juvenile feathers, and adult feathers. Thermal down starts growing at about ten days, juvenile deck feathers at about 20-23 days and juvenile flight feathers at about 27 days, but feather growth doesn't overtake structural growth until thirty-five to forty days after hatch. Flight muscles also begin growing as eaglets wingercize, flap, hover, and eventually branch and fledge.

Stage 3 - Neurological Coordination. Eagle watchers know how ungainly eaglets can seem! As they grow, they become more adept at controlling beaks, legs, wings, and feet. They learn to stand on their own feet, tear food, self-feed, and flap their wings, going from cute but clumsy clown clompers to graceful young eaglets poised at the edge of fledge.

So where is our cortical homunculus in weeks 3-4? I'd tend to think that legs, feet, and wings are accelerating in importance this week, leading important behaviors like standing, tearing, and flapping! I also wonder what impressions are being made now that they are beginning to pay attention to the outside world. The nest and eagles always have more to teach us!

Things that helped me write this blog, with a few considerations:

Monday, April 10, 2017

Eaglet Growth and Development, Week Two

It is April 10 as I write this, and our eaglets are growing rapidly! In Decorah, D26 is 10 days old, D27 is 9 days old and D28 is 6 days old. At Decorah North, DN4 and DN5 are 12 and 11 days old. And at Fort St. Vrain, FSV34 and FSV35 are 15 and 13 days old.

D26. See the earhole?
In their second week of development, the eaglets will gain roughly two pounds between their 7th and 14th day of life. They will experience rapid growth in features like beaks, culmens, and footpads, start replacing their white natal down with thicker grey thermal down, and begin exploring the nest. Although they aren't yet standing on their toes, they are able to sit up - way up! - for feeding and shuffle around on their metatarsi. Their eyes are wide open and fit more comfortably in their eyesockets, features like brow ridges are beginning to appear, and their legs and footpads are yellow, not pink. Gary Bortolotti wrote that bald eagles might gain more weight per day than any other north American bird, although the majority of their weight gain occurs within the first 30-40 days. This rapid weight growth is fueled by their nutrient-rich diet of meat. Over the past week or so, we watched the eaglets chow down on fish, roe (fish eggs), rabbit, squirrel, unidentified birds, and prairie dog. Poop is beginning to streak the poopcasso tree and crib rails as the eaglets become more proficient at shooting poop out of the nestbowl. While babylet battling hasn't entirely subsided, it has become less intense as pecking orders are established and eaglet crops are repeatedly stuffed until they look ready to burst!

Ma provides shade for FSV34 and FSV35
The Fort St. Vrain eaglets are the oldest of the group. Watcher Donna Young wrote that "We have two eaglets that are already quite adventurous. They are moving about the big nest. One climbed up onto the fence rails yesterday, but found its way down too. It may become a true Colorado mountaineer!" This is in line with past years at Fort St. Vrain, where a large nest and warm temperatures seem to lead to earlier wandering. Cold is a challenge to eaglets under 10-15 days of age, but so is heat! With little ability to control body temperature and no way to lose heat except by panting, the eaglets did their best to retire to what little shade tree limbs and the nest itself offered. Ma FSV also provided shade for the eaglets by moving from one to the other and standing between them and the sun.

In the week to come, we can expect (continued) rapid growth in footpads, talons, and legs. Beak growth will rapidly slow as the eaglets' beaks approach adult size and we may see dark juvenile feathers start to sprout from their grey down. Overall weight and height gain will continue, most likely reaching their steepest curves some time this week. By the end of their second week of life, our little bobbleheads at Decorah, Decorah North and Fort St. Vrain will be almost a foot tall! Enjoy eaglet earholes and egg teeth while you still can - their earholes will soon be covered by down and their egg teeth are wearing away.

Let's talk a little bit about 'parenting styles'. Last year, watchers observed that Dad North was less involved in feeding his eaglets directly, although he participated in a lot of bucket brigade feedings. The North eagles didn't tend to stockpile prey and food often seemed scarce at the North nest. Given the differences between Dad Decorah and Dad North, some watchers speculated that Dad North was on his first round of eaglets. While we didn't weigh in on that discussion, we have seen changes this year. The North's nesting chronology moved ahead by almost one month to match that of the Decorah eagles. While Dad North still offers the bucket brigade from time to time, he is participating in more tandem feedings with Mom North. When feeding solo, Dad North often offers food to both eaglets, picks up dropped food and re-offers it, and removes grass from their beaks. Food seems plentiful compared to last year, with fish after fish coming into the nest for DN4 and DN5. Using feeding and food availability as benchmarks, Dad North has undeniably become more skilled at some aspects of eagle parenting. Like flying, parenting is instinctual - but proficiency is learned.

Tandem feeding, Dad and Mom North. Dad North (at left) is feeding DN5. Mom is feeding DN4
As John pointed out, food availability in the nest reflects food availability on the ground. In late March, suckers are spawning, trout are actively feeding on emerging and hatching insects, rabbits and other mammals are leaving their winter dens and grounds (often with young in tow), and flocks of birds are migrating through the area. This rush of food comes at the perfect time for newly hatched eaglets - something Mom and Dad North appear to be taking full advantage of this year! The Fort St. Vrain nest is also piled high with prey, including prairie dog. If the weather stays warm, we might see turtles join the list as streams and smaller water holes shrink. Look for turtle plastrons at the bottom of the Fort St. Vrain nest!

The general stages of eagle development are:
  • Stage 1 - Structural growth. In their first thirty-five to forty days of life, eagles grow very rapidly, gaining weight and building bones, muscles, tissue, and features like tarsi, footpads, toes, and claws. This phase of development slows down about halfway through an eaglet's time in the nest, even though individual features might continue some level of growth. 
  • Stage 2 - Feather and flight-related growth. Eagles grow four sets of feathers - natal down inside the egg, thermal down, juvenile feathers, and adult feathers. Thermal down starts growing at about ten days, juvenile deck feathers at about 20-23 days and juvenile flight feathers at about 27 days, but feather growth doesn't overtake structural growth until thirty-five to forty days after hatch. Flight muscles also begin growing as eaglets wingercize, flap, hover, and eventually branch and fledge. 
  • Stage 3 - Neurological Coordination. Eagle watchers know how ungainly eaglets can seem! As they grow, they become more adept at controlling beaks, legs, wings, and feet. They learn to stand on their own feet, tear food, self-feed, and flap their wings, going from cute but clumsy clown clompers to graceful young eaglets poised at the edge of fledge. 
 I'm not sure how familiar many of you are with the cortical homunculus, an image-based tool that maps tactility. While useful and extremely cool, most cortical homunculii are static - that is, they reflect just one phase (usually adult) of an organism's life. But an eaglet's cortical homunculus will differ from an adult's as body parts and associated skills are gained and neural pathways developed. Our eaglets' brains and bodies are rapidly growing and changing as they gain the skills they need for life outside the egg! I'd tend to think that visual acuity suddenly 'lit up' this week, leading changes in coordination as the eaglets began sitting up and moving around.

Things that helped me write this blog, with a few considerations:

Friday, March 31, 2017

Why a functioning EPA is important for birds

The EPA, or Environmental Protection Agency, is a US government agency established in 1972 to protect human health and the environment. By the early 1970's, Americans were increasingly aware of the dangers posed by pollution, the indiscriminate dumping of sewage and industrial chemicals, and the widespread and unregulated use of pesticides, herbicides, and toxic agents. Peregrine falcons, bald eagles, and other birds were critically endangered and at risk of extinction, the Cuyahoga river had famously caught fire several times, Great Lake Erie had been declared dead, and smog regularly blanketed America's largest cities. People were organizing at local, state, and national levels to get ordinances and laws passed to reduce pollution and penalize polluters. In some cases, people were driven by concerns about the future, but in many others - like Los Angeles - they were concerned with immediately improving health and saving lives.

Prior to the Clean Air Act, the Clean Water Act, and the EPA, there were no legal or regulatory federal mechanisms to protect the environment. While communities could address local problems, water and air don't have a fixed address. A regulatory mechanism was needed that would allow enforcement across county and state lines, address pollution on land and waterways owned by the federal government, and provide funds for cleaning up large, extremely toxic messes like this one, which is still affecting the Channel Islands. Following the introduction and passage of several bills related to environmental concerns, President Nixon proposed a new agency on July 9, 1970, to consolidate the environmental responsibilities of the federal government. Congress approved the proposal and President Nixon signed an executive order establishing the EPA on December 2, 1970.

Why does this matter to human health and wildlife?  Take a look at the EPA A-Z index: The EPA is able to regulate and enforce environmental and human health laws as related to air (the Clean Air Act and Amendments), water (the Safe Drinking Water Act, the Clean Water Act, the Water Quality Act, and the Safe Drinking Water Amendments), land (the Wilderness Acts, the Wild and Scenic Rivers Act, and the Surface Mining Control and Reclamation Act), endangered species (the Marine Mammal Protection Act, the Endangered Species Act, and the Endangered Species Preservation Act), Hazardous Waste (the Solid Waste Disposal Act, the Resource Recovery Act, and the Hazardous and Solid Wastes Amendments Act) and human health (the Federal Environmental Pesticide Control Act, the Toxic Substances Control Act, the Nuclear Waste Repository Act, and the Food Quality Protection Act). In short, the EPA played a very important role in the cleaner air, the cleaner water, and the formerly endangered species we so enjoy today.

Perhaps most important to bald eagles, peregrine falcons, brown pelicans, and many other birds, the EPA banned DDT in the United States in 1972 based on its adverse environmental effects. But that isn't the only banned chemical that affects birds. Remember DN2's death last year? He was poisoned by methomyl, a member of the carbomate chemical family. Carbofuran, a related chemical, killed millions of birds each year before the EPA canceled it for use on crops in 2009. In 1990, diazinon was classified as a restricted ingredient and banned for use on golf courses and turf farms, marking the first time regulatory action was taken specifically on behalf of birds. It was banned entirely on January 1st of 2005. Chlordane was banned for home, garden and agricultural uses in 1983. It is persistent in the environment and still poisons birds today, but not at the levels it once did. Monocrotophos was removed from use in the United States in 1991, although it was linked to huge die-offs of Swainson's Hawks on their wintering grounds in Argentina. You can read more about the American Bird Conservancy's successful intervention here.

So in short, a working EPA is important for birds because its actions have directly benefited many birds including eagles and peregrine falcons, and its enforcement of environmental laws has resulted in cleaner air, cleaner water, and better health. Concerned only with the economy? The estimated economic benefit for banning lead ranges from $110 billion to $319 billion for each year's newborns. The yearly economic benefit of that alone is far bigger than the EPA's annual budget.

So what can we do? In the short term, you have until May 15, 2017 to comment on Executive Order 13777, issued on 2/24/17, which directs agencies to establish a Regulatory Reform Task Force to make recommendations about potential repeal, replacement, or modification of EPA regulations. We know it sounds boring and unimportant. We know that a lot of people who follow the eagles have busy lives. We know that our fans come from all over the political spectrum. But conservation isn't red or blue, it is important to birds and humans, and we are asking people to take the time to read through the materials and comment.

Why?  We asked you to comment on the 30-year take of bald eagles, and you did. Did the 30-year take pass? Yes. But while it would have been good to see it voided, your comments resulted in a better ruling overall, with more safeguards put into place and outside auditing of companies that choose to participate in the 30-year take program. Without your comments, it would have been a lot worse.

If you would like to read more about the EPA and birds before commenting, follow these links:

In the long term, you can educate yourself and others about the substances most toxic to birds. You can support organizations that advocate and do research on behalf of birds. Of course I like it when people support the Raptor Resource Project, but you should also take a look at the American Bird Conservancy and the work they do. You can get involved in local projects: remember, our national concern for the environment grew in part out of local issues, whether it was choking smog, the loss of soil, the contamination of water, or the need for local parks and wild land. We can all keep reminding our congressional representatives and senators that conservation and the environment are important to us. And we should all take strength, determination, and resolve from our polluted past: strength, since we have made significant improvements; determination, so we can keep moving forward; and resolve that we won't go back to those days again.

Things that helped me learn and write about this topic:
Keep in mind - we've come a long way, baby!

Eaglet Growth and Development: Week One

We are watching eaglets at three nests right now: Decorah, Decorah North, and Xcel Energy Fort St. Vrain. The oldest (FSV34) is five days old, and we're still waiting for DN6 and all of the Decorah eaglets as I write this. What can we expect in the first week of watching? Weight Gain!

DN4 at the Decorah North Nest
Like humans and other animals, growing nestlings have developmental milestones. The eaglets spend roughly the first week of their life gaining weight. They aren't able to thermoregulate yet, so depending on the weather and temperature, they may spend a lot of time under Mom and Dad. We'll see them eat, sleep, scuffle, and grow stronger as they interact with one another.  They will go from roughly 3.2 ounces - about the weight of 18 nickels - to roughly 16 ounces or one pound, increasing their weight five times over in just seven days.

Weight gain (g/day) as a function of age for male and female nestling Bald Eagles
This chart was reprinted from The Wilson Bulletin 96: 527 from an article published by G. R. Bartolotti (1984) with the written permission of the Wilson Ornithological Society. 
Many structural features, including foot pads, tarsi, and hallux claws, won't start rapid growth until 10-15 days after hatch. But the hatchlings' mid-toes and culmen - the dorsal ridge of the upper mandible - are already growing longer! Food is the root of all else besides, so it isn't surprising that the culmen achieves maximum growth in the first ten days. I suspect that the mid-toe aids balance, a crucial element of sitting up and exploring the nest. While our eaglets won't truly stand on their feet until they are roughly four weeks old, they will begin to shuffle around the nest on their tarsi long before that.

Enjoy the downy bobbleheads this week! By next week, they will already be growing their longer 'wooly' second or thermal down and alternately worrying and thrilling us with their interactions and sojourns around N2B.

The general stages of eagle development are:

  • Stage 1 - Structural growth. In their first thirty-five to forty days of life, eagles grow very rapidly, gaining weight and building bones, muscles, tissue, and features like tarsi, footpads, toes, and claws. This phase of development slows down about halfway through an eaglet's time in the nest, even though individual features might continue some level of growth.
  • Stage 2 - Feather and flight-related growth. Eagles grow four sets of feathers - natal down inside the egg, thermal down, juvenile feathers, and adult feathers. While thermal down starts growing at about ten days and juvenile flight feathers at about 27 days, feather growth doesn't overtake structural growth until thirty-five to forty days after hatch. Flight muscles also begin growing as eaglets wingercize, flap, hover, and eventually branch and fledge.
  • Stage 3 - Neurological Coordination. Eagle watchers know how ungainly eaglets can seem! As they grow, they become more adept at controlling beaks, legs, wings, and feet. They learn to stand on their own feet, tear food, self-feed, and flap their wings, going from cute but clumsy clown clompers to graceful young eaglets poised at the edge of fledge.

I'm not sure how familiar many of you are with the cortical homunculus, an image-based tool that maps tactility. We discussed it very briefly in this blog and I'll include links below. While useful and extremely cool, most cortical homunculii are static - that is, they reflect just one phase (usually adult) of an organism's life. But an eaglet's cortical homunculus will differ from an adult's as body parts and associated skills are gained and neural pathways developed. Our eaglets' brains and bodies are rapidly growing and changing as they gain the skills they need for life outside the egg!

Things that helped me write this blog, with a few considerations:

Thursday, March 23, 2017

What's inside those bald eagle eggs?

It is 31 days since egg number one was laid in Decorah, 32 days since egg number one was laid at Decorah North, and 36 days since egg number one was laid in Fort St. Vrain. We are starting hatch watch for Fort St. Vrain on Saturday, Decorah North on Sunday, and Decorah on Monday. The embryonic eagles are either in or approaching their final stages of development now, but what did they look like as they developed and grew inside their eggs?

Dr. Peter Sharpe from the Institute for Wildlife Studies developed a table of bald eagle embryonic development based on work done by Hamburger and Hamilton (1951). While not all bald eagle eggs hatch in 35 days, the stages of development look something like this...

Development of a chick, drawing from Frank Lillie photos. Artist William Sillin
From 0 to 4 days: A single cell is formed by the union of sperm and egg. It divides into multiple cells and forms layers. Head and tail are established, the emerging embryo divides into blocks called somites, and basic life support structures begin to develop, including the nervous system, skin, circulatory system, gastrointestinal system, and optical system.  The embryo turns onto its left side. Its heart begins to beat roughly 72 hours after incubation begins.
Chicken embryo at roughly two days incubation: equivalent to an eagle at about 3.5 days
At four days of age, the embryonic eagle doesn't look anything like a bird, but it has inside and outside layers, it can transport materials through its developing circulatory system, and its nervous system has an anterior-to-posterior template in place. The brain and nervous system will continue to grow and change, but the stage is set for the development of a skeletal system, limbs, a beak and tongue, foot and wing digits, and organs. 

From 3.5 to 9 days: The amnion closes, sealing the developing embryo inside the egg's innermost membrane. The allantois forms to sequester liquid waste and exchange gases through the porous eggshell. Wings, tail, and leg buds form. Eyes develop pigment.  Leg buds grow larger than wing buds and limbs begin to form. Elbow and knee joints are distinct by roughly 8 days and digital grooves - the precursors of toes and wing structures - are distinct by roughly nine days. The embryo's beak and tongue begin to form.
Chicken embryos roughly 23 to 25% of the way to hatch
At nine days, the minute embryonic eagle is about 25% of the way to hatch and still doesn't look especially birdlike. It has a head, eye pigmentation, stiff differentiated limbs, the beginnings of a beak, rudimentary digestive organs, and a defined sex. The stage is set for further organization as the embryo develops an egg tooth, true eyes, and feather germs. 

From 11 to 17 days: The egg tooth and two scleral papillae form on the 11th-12th day. Limbs are bent. Dorsal feather germs form on the 12th day. A nictitating membrane is visible on day 13. Ventral feather germs develop, the eyelids begin closing, and flight feather germs develop. 

A chicken embryo roughly 50% of the way to hatch
At 17.5 days, we are roughly halfway to hatch. Our embryo's head is disproportionately large, but it is definitely a bird. It has a beak, distinct toes, bent limbs, and eyes that take up most of its head. Its eyes and eye cavities aren't done forming and it needs to develop scales, nails, rough pads and spicules, and down feathers. Its yolk sac and small intestines are still outside its body cavity, and it has a lot of growing to do!

From 18 to 23 days: Leg scales, tiny talons, and plantar food pads appear. The eyelids are almost closed and the eyes are no longer quite as large in proportion to the rest of the head.

We are 65% of the way to hatch! Other than the closing of the body cavity, most major morphological changes are done. The eyelids will close, the eyes will grow into their sockets, the eaglet will develop natal down, it will internalize its egg yolk sac, its body cavity will close (leaving behind an egg yolk sac scar) and it will position itself for hatching! 

So what happens right before hatch? Just a few days from external pip, the rapidly growing embryo is taking up nearly all the space in the egg. It...
  • Turns so that its head is at the large end of the egg next to the air space.
  • Pierces the internal membrane - the internal pip - and begins to breathe air with its lungs. Hatch has started!
  • Takes the yolk sac into its body as it consumes most of the remaining albumen and yolk. 
  • Grows enough to contract the hatching muscle, pointing its head up and positioning its egg tooth against the shell of the egg. The eggshell is thinner and weaker than when it was laid, since the growing embryo absorbed calcium from the shell for its bones. 
  • Rubs its egg tooth against the shell, which cuts a small hole. We have an external pip!
  • Rotates its body, slowly cutting a ring around the shell.
  • Pushes its body against the shell, forcing the shell apart.
  • Works itself free of the shell membranes and halves. The eaglet has landed and hatch is complete!
We are looking forward to hatch later this week! Curious about what's in store? Watch this 2015 video of the very final stages of hatch in N2. 

Illustrations were taken from Popular Science Monthly/Volume 71/September 1907/The Problem of Age, Growth and Death III:  Link. Thanks to artist William Sillin for allowing us to use his lovely illustrations: (check it out - his illustrations are very cool!). Also take a look at this cool plate by Keibel and these lovely photos of chicken embryos:

Things that helped me learn about this subject:

Tuesday, March 21, 2017

Body plans and BOP shapes

Since we are watching bald eagles and peregrine falcons, I wanted to talk a little bit about body plans and their influence on flight, hunting, and prey base. As watchers know, eagles are soaring generalist hunters that eat almost anything they can sink their talons into, while peregrine falcons are energetic, acrobatic flyers that specialize in catching birds in the air. Both are birds of prey, but their body plans and wing shapes result in very different lives.

Body plans, size, and flight
With their long, broad, slightly rounded wings, large wing slots, and broad, wedge-shaped tails, bald eagles are built for soaring. They hold their wings flat and save aerial acrobatics for hunting and encounters with other birds. While tail winds and thermals aren’t absolutely necessary for eagle flight, their migration corridors and styles take advantage of both. Thermal winds are powered by sunlight, which means that eagles migrate during the day. They also tend to prefer wind corridors, including ridgelines and funnels that concentrate and amplify wind – think of the cliffs of the Mississippi river or the tight river valleys and ridges of NE Iowa. A stiff tail wind will send migrating eagles aloft in their thousands, especially over surfaces with little opportunity for thermal soaring. The Bald eagle body plan and low-aspect wings - large, broad wings relative to its overall surface area - is most suited to low-angle, low-energy soaring flight.

Unlike bald eagles, Peregrine falcons are built for speed and maneuverability. They have long, narrow, pointed wings and long tails shaped for diving, twisting, and turning in flight. Where eagle flight is flat, peregrines often fly in a series of arcs as they dive, dash and pursue other birds in flight. The peregrine body plan and high-aspect wings - narrow, pointed wings relative to its overall surface area - is most suited to high speed, energetic and often acrobatic powered flight.

Bald eagle silhouette
Peregrine falcon silhouette

Although I don't confuse falcons and bald eagles, I often find body plan and flight style to be very helpful in identifying similarly-sized birds of prey at a distance. Is it large and flying flat, holding its wings in a vee and tilting as it flies, or M-shaped? If you are in northeastern Iowa, the first is probably an eagle, the second is probably a turkey vulture, and the third is probably an osprey. Are the wings large or small in proportion to the rest of the bird? Are its wings pointed or rounded? Is its tail long or wedge-shaped?  Is it flapping and gliding, diving, hovering, or quartering low over a field? Did you see it in the woods or in the open? Body plan, behavior, and habitat are very helpful in identifying birds of prey, especially at a distance.

Silhouettes of birds of prey in flight from
Body plans, hunting, and prey base
In general, all birds of prey have keen vision, talons, and curved beaks to help them hunt, kill, and eat prey. But not all beaks, talons, and hunting styles are the same. The peregrine falcon’s speed and maneuverability makes it uniquely suited to catching birds in flight, while a bald eagle’s size, strength, powerful feet, and long talons make it an excellent generalist hunter. Both birds take full advantage of their very different body plans when it comes to catching and eating prey.

A peregrine's high speed, high angle dive
A bald eagle's lower speed, lower angle flight

A peregrine falcon’s speed and maneuverability allow it to fly high, dive steeply, and hit prey so hard that the force of impact severs its prey’s spinal cord. A peregrine begins its dive by rolling, cupping its wings around its body, and tucking in its feet, yielding an aerodynamic raindrop that slices through the air at high speeds.  Special cone-shaped bones in its nostrils – an adaptation unique to peregrine falcons – allow it to breath while diving at speeds of over 200 miles per hour.  As the falcon approaches its prey, it extends its feet, brakes sharply, and snatches it out of the air with its long, slender toes and sharp talons. If hitting a bird doesn’t kill it, peregrine falcons use their tomial tooth – a special notch in their beaks that bald eagles don’t have – to sever their prey’s spine. While a peregrine’s feet are strong and quick – great for grabbing and slashing attacks – they don’t have the crushing strength of a bald eagle and their diet is largely restricted to other birds. 

A bald eagle’s large size, soaring flight, and strong feet help it to take a wide variety of prey, although its speed of attack is slower, its angle of attack is lower, and it usually kills prey with its feet. As we’ve seen at the fish hatchery, Mom and Dad swoop shallowly over the retaining pond, braking heavily as they plunge their feet into the water and pull out trout. Without stopping, they fly into a tree, on to the bluff, or into the nest, crushing or stabbing the trout with their powerful feet and sharp talons. Although they have special adaptations called spicules – rough bumps that help them grip slippery fish - bald eagles don’t specialize in any one kind of prey, and their size, strength, powerful feet, and fishing ability give them access to an extremely wide prey base.

Again, falcons and eagles are very different and I don't confuse the two, even at a distance. But understanding how body plans influence birds is useful to understanding their lives and identifying them in the field. I find it to be more helpful overall than looking for hard to see features, especially if a bird is far away. 

Hashtag #musing: could body plans impact gregariousness? Off their breeding grounds, bald eagles are quite gregarious. Their flashy colors, large, visible body plans, and wind-seeking behavior often bring them into proximity with other eagles. Eagles compete (think piracy and kleptoparasitism) but they also eat a wide variety of prey and often benefit from following other eagles when searching for food. As far as we know, peregrine falcons are loners. During migration or following dispersal, there can be multiple peregrines in a site with an abundance of food. However, they aren’t gregarious. Perhaps their more solitary behavior is driven in part by a body plan that results in a restricted prey base (leading to serious food competition), no real benefit to stealing or attempting to steal food, and less congregation around important dynamic and thermal soaring points.

Did you know?
A turkey vulture "V" is more correctly referred to as a dihedral. Turkey vultures are masters of soaring without flapping as they ride the wind in search of carrion. How do they do it? As wind strikes one wing or another, tipping the vulture right or left, one wing tips high and the other tips low. Wind flows under the low wing, pushing the vulture and righting it until it tips again. This allows them to exploit the smallest of air currents as they soar lowly and slowly through the sky. While they sacrifice some maneuverability, their food - carrion - doesn't require agility to catch.

Harriers also engage in dihedral flight, but their food - small mammals, reptiles, amphibians, and birds - requires considerably more agility. Compare their body plan with that of a turkey vulture. Dihedral flight allows them to soar very slow and very low, but they have a long tail and wings more like a falcon, which helps them roll and twist when needed. Harriers are a very interesting bird of prey: visit Cornell's website to learn more about them!

And finally, I've seen some interesting conundrums when people compare birds to aircraft. Remember that aircraft can't change their shape to respond to wind conditions or the need to rapidly change position. But birds can and often do change shape as they fly! I chose silhouettes that I thought best represented each bird overall, but birds might adopt different flying styles under different conditions, even if they can't change their overall body plan.

Things that helped me learn about this topic