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': https://youtu.be/Rua_nnLF6TE

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: https://youtu.be/HyVFISzaqOQ. 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!

Links
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: https://raptorresource.blogspot.com/2015/08/falcon-effigies-of-upper-mississippi.html. 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 (https://youtu.be/IPkJ6kgYFHs). 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: https://www.epa.gov/environmental-topics/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: http://www.willsillin.com/ (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: http://www.microscopy-uk.org.uk/mag/artnov04macro/mlchicken.html.

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 learner.org: http://www.learner.org/jnorth/tm/HawkPrimer.html
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! https://www.allaboutbirds.org/guide/Northern_Harrier/lifehistory

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