Wednesday, December 30, 2015

Birds and Nest-Building

This blog was inspired by the paper 'The design and function of birds' nests', Ecology and Evolution 2014; 4(20): 3909–3928. It can be found here:

Hard at work on N2B
What determines the design of a bird's nest? You know the type of nest I'm talking about, right? A bald eagle's large platform nest, built with sticks, high up in the branches of a tree.  Or maybe a scrape created in dirt or gravel on a shallow cliff ledge by nesting peregrine falcons. How about the burrows created by bank swallows and belted kingfishers, or the cavity nests excavated in trees by woodpeckers? Or am I thinking of the pendulant and sometimes very elaborate suspended nests created by orioles and weavers?

When I think of bird nests, I think of the classic small cupped nests I collected as a child. But birds nest in a variety of ways and places, creating nests from twigs, sticks, moss, grass, fur or hair, roots, bark, leaves, pine needles, feathers, lichens, paper, insect cocoons, snakeskin, saliva, and other materials. They nest high in trees, but they also nest on the ground, under the ground, in the darkness of chimneys and caves, and even in active wasp nests. Some birds construct elaborate nests while others get by with a shallow scrape in a stolen or abandoned nest.

Nests traditionally have been thought of as nothing more than places for birds to lay eggs and raise young. It was assumed that natural selection and the need to minimize the risk of predation determined the design of completed nests. However, recent research has found that sexual selection, parasites, and the need to build a nest that can handle variation in weather conditions (which we certainly see in Iowa, Colorado, and Minnesota!) also play significant roles in influencing nest design.

Sexual Selection
How does sexual selection play a role in nest design? It goes something like this: birds that build awesome nests relative to other members of their species must be healthy, high-quality mates. Think about Decorah. Mom and Dad spend a lot of time procuring and hauling wood and soft materials into the nest. This is a costly activity energetically speaking, and it requires both eagles to be in good shape - well-fed (which implies provisioning ability), skilled at flying, and relatively parasite-free. While different things might indicate quality to different species of birds, it appears that large nests signify quality among bald eagles.

Bald eagle nests are bi-parentally built - that is, both parents work on them. However, in Decorah it is Dad who spends the most time getting the sticks just right, scraping in the nest bowl, and preparing the egg cup. Studies have found that female magpies adjust their reproductive effort in relation to the male's nest-building activities. The more time he spends working on the nest, the more time and energy she puts toward reproductive processes, including copulation.

What could we watch for in our eagles? A study of male house sparrows found that they call to females when adding feathers to the nest, suggesting that they wish the behavior to be observed. The volume of feathers delivered by males was positively correlated with clutch size and female provisioning rates. While Dad doesn't usually vocalize when he places a stick, he often interacts with Mom in some way - taking a stick from her, moving sticks while she is in the nest, and so on. His obsession with proper placement might be his way of signaling fitness and getting more tailfeather from Mom to boot! I'm going to pay more attention to Mom and Dad's interactions during and following their sticky adventures!

While the paper doesn't touch on intelligence, it is hard for me to believe that it isn't part of the total sexual selection package. Building a nest is a lot harder than it looks and requires a whole host of things: access to food (which implies hunting ability and understanding of a territory, among other things), strength (which implies access to food and a body relatively free of parasites), and flight skills (ditto). An intelligent bird will presumably make better decisions about maximizing energy gain, procuring food, and hauling and placing sticks. Its intelligence should help it live longer and build a sexier nest, which in theory will lead to more copulation, more fertilized eggs, and offspring that inherit Mom and Dad's traits.

Bird parasites include lice, fleas, flies, mites, ticks, leeches, fungi, and bacteria. We've seen firsthand the damage that blackflies and hippoboscids can do: killing young falcons, driving young from the nest to early, and delaying development. Birds have a wide variety of responses to parasites, including molting feathers, the use of feather toxins, preening, and maintaining their nests.

Watchers might remember Stitch and Spot, the red-tailed hawks from Eaglecrest Wildlife. Male Spot brought green plant material into the nest on a regular basis. The greenery (probably blue oak branches) contained high levels of monoterpenes and isoprene, which helped reduce parasites and fungi and may also have signaled fitness to female Stitch in the same way that a large nest might signal quality to a female eagle [a blog on greenery and parasites can be found here].

However, the bald eagles we watch don't appear to intentionally carry greenery into their nests. So what do they do? Many watchers have commented on the number of mice in the nest. For the mice, an eagle's nest offers food (scraps of protein and stomach and crop contents of prey), shelter, and safety from serious mouse predators like fox and owls. While bald eagles would eat a mouse, it isn't much more than an hors d'oeuvres compared to prey like pigeons, trout, squirrels, and so on, so the risk is well worth the payout! In return, mice devour leftovers and help keep the nest a little cleaner and presumably parasite-free than it would be otherwise. As with greenery and hawks, sexual selection might drive a nest-building behavior that also repels undesired guests!

An early nesting season also helps reduce parasitization of young, although it means parent birds need to be ready for the challenges that winter brings. This leads us to...

Environmental Adjustment
Remember 2013? The birds we watch produced young in the teeth of the worst winter since the 1970s. Our eagles were successful in part because the design of their nest influences the microclimate in which eggs and young are incubated. Dad's attention to the nest bowl - rolling, scraping, nest digging, and the careful arrangement of soft materials to form a cup once the substrate is suitable - may both excite Mom and result in a structure that can weather rain, snow, and serious sub-zero temperatures. Of course, if you watch the eagles, you have probably already realized that the types and placement of materials aren't accidental. We've seen the nest bowl and cup carefully prepared ahead of time, and we've seen Dad bring grasses and husks to tuck around Mom while she incubates eggs.

So the next time you watch a bird build a nest, either online or off, remember that much more is going on than meets the eye. Sexual attraction, courtship and flirtation, proof of fitness, and protection of young from parasites and weather all appear to play important roles in the design of finished nests.

Things that helped me learn and write about this topic:

Did you know that?
There is a bird that nests inside a wasp's nest! Follow this link to read more about the Violaceous Trogon and its extreme housing practices!

Monday, November 30, 2015


We have a day for giving thanks. We have two for getting deals. Now, we have #GivingTuesday, Tuesday, December 1st, a global day dedicated to giving back! If you like the work we do, please consider making a donation. You can donate online via paypal or mail a check to the Raptor Resource Project, PO Box 16, Decorah, IA 52101.

We are celebrating #GivingTuesday with some very special guests on our Decorah Eagles Ustream channel at We'll be starting chat at 8:00am Central Time and running through 8:00pm. Our planned schedule (weather permitting) will be:

10:30  Intro - John Howe
11:00  PE Project Update - Neil & Laura
12:00  Trapping and Monitoring - Dave Kester
3:00  Cameras and Projects Update

We will take questions from chat, although you are also welcome to email questions to I can't guarantee we will get to all of them, but please feel welcome to send them!

What does the Raptor Resource Project do? We are a 501c3 that specializes in the preservation of falcons, eagles, ospreys, hawks, and owls. In addition to bringing you the Decorah Eagles, Great Spirit Bluff Falcons, and other birds of prey, we create, improve, and directly maintain over 50 nests and nest sites, provide training in nest site creation and management, and develop innovations in nest site management and viewing that bring people closer to the natural world. Our mission is to preserve and strengthen raptor populations, expand participation in raptor preservation, and help foster the next generation of preservationists.

As a nonprofit environmental organization, we depend on donors, research, and our other programs for our entire budget. With your tax deductible contribution to the Raptor Resource Project, we can:
  • Continue updating to high definition digital cameras in Decorah and elsewhere.
  • Help develop and realize a dream of Bob's:  establishing a Philippine Eagle cam to save a beautiful bird of prey who's very existence is threatened. We are working in cooperation with the Cornell Lab of Ornithology and the Philippine Eagle Foundation. Neil and Kike will be traveling to the Philippines to scout locations with staff from both organizations in February of 2016.
  • Provide one of the world’s largest public wildlife education programs to countless classrooms through our unequaled Ustream channels, interactive chats, facebook page, and blog.
  • Partner with landowners, private businesses, and government agencies to monitor and band peregrine falcons at over 40 sites. 
  • Continue our collaborative raptor nest-box, trapping, and monitoring programs.
These things all take money. As of 2015, our annual expenses were hovering around $99,000 per year:

  • Staff/Compensation costs were around $55,000. We incurred extra expenses for our N2B build and two camera installs: one at N2B and one at Decorah North Nest. These were intensive projects that required a lot of help. The N2B camera installation alone took five full days of work from dawn past dusk.
  • Equipment – computers, camera upgrades and maintenance, tools, encoders, software, transmitters, and so on – cost around $27,400. 
  •  Supplies – primarily cable, tools, climbing equipment, banding equipment, bands, installation hardware, maintenance equipment, and lumber – cost around $2200 annually.
  • Internet access costs roughly $4,500 annually.
  • Other/Miscellaneous costs around $9,000 annually. This category includes gasoline, electricity, travel-related costs, equipment fabrication, and propane so we can heat the shed!
Our income is generated entirely by donations from viewers of our various cams, and we sincerely appreciate your generosity and support of the Raptor Resource Project mission. Would you please help us make a difference with your donation?

Thank you so much for your support and we hope you enjoy watching in 2016!

Friday, November 13, 2015

How Much Can A Bald Eagle Carry?

On November 4th, photographer Alex Lamine photographed the female bald eagle at Berry College carrying a very large stick. The Berry College Eagles Facebook page posted: "Today, photographer Alex Lamine caught an extraordinary occurrence at the nest. Around 7 a.m., as morning light began to creep into the sky, Alex watched Mom Berry gnaw a limb off a tree and begin flying it toward the nest tree. She carried the long limb in her good (right talon) and Alex captured the action. Immediately after, Mom dropped the limb and it landed just a few feet from Alex. It impaled the earth on the heavy end and could have caused a serious injury. Eddie Elsberry weighed the limb later today and it weighs 12 pounds! We've seen both eagles drop limbs from time to time but this is the largest by far that we have seen. Thanks, Alex, for sharing your experience with us. It is truly amazing that she could carry such a heavy limb in one talon!"

We immediately started getting questions about the stick. Could an eagle carry twelve pounds? Was she carrying the stick, or was it actually falling as she held on to it? We've speculated quite a bit about how much weight eagles could carry, but I decided to skip the musing this time and ask some experts. I ended up talking with Professor Jim Grier (Grier has studied birds of prey extensively and owned a golden eagle), Brett Mandernack, Neil Rettig, Chuck Sindelar (a good friend of Bob's who was deeply involved in bald eagle recovery), Jon Gerrard (who wrote The Bald Eagle: Haunts and Habits of a Wilderness Monarch with Gary Bortolotti), and Professor David Bird (among other things, the author of The Bird Almanac, A Guide To Essential Facts and Figures of the World's Birds). It was quite a group of experts, to be sure!

Several of them noted that the amount of weight a bird could carry was highly dependent on the situation, including:
  • Wind direction and speed
  • How the object was carried. Was it streamlined or catching the wind?
  • How dynamic the object was. Did it dangle and swing, or stay steady?
  • How the object was captured. Was it caught and carried in flight (with momentum) or dead-lifted from the ground?
  • The direction the object was being lifted in. Was the object being lifted up or down?
Professor Grier compared eagles with aircraft and talked about dynamics, flight conditions, and how the object was carried: "I sometimes got the impression that my golden eagle could carry as much or more in his crop than in his feet, but never got any good measurements or wrote down details. For example, he could capture a large rabbit that he could not fly with...but then he'd eat most of it and be able to fly with a really full crop. I think the trim of the eagle, as in airplanes, and drag/balance of carried items, is important." He added: "Flight conditions make a big difference, particularly at the limit of weight, as with aircraft. The best conditions are high air pressure with a steady wind plus room and conditions for a good take-off, all of which affect the ability to get airborne and then stay airborne. I've seen bald eagles carry large fish under some conditions, for example, that they couldn't under other conditions."

Think of an airliner. Cargo is balanced around the center of gravity inside the plane, not dangling below it. According to the FAA, center of gravity deviations as small as three inches can dramatically change the handling characteristics of some fully loaded aircraft. When Jim's golden eagle ate a large rabbit, it was for all practical purposes 'balancing' the cargo in its crop, which is located in the center of its neck above the top of its chest. In this case, balance was a bigger issue than weight as far as lift and stable flight were concerned. For more information on how the center of gravity affects flight, watch this video:

Chuck Sindelar wrote about watching golden eagles play with sticks outside of nest-building season. "They would fly off with a stick and gain altitude by circling. A second golden eagle would follow the first up into the sky and would get into a position where,  when the first bird with the stick dropped it, the second bird would dive and regrab it, often before the stick reached the tops of the trees below. Sometimes he would have to pull out of his dive and allow the stick to hit and enter the trees, and then both birds world move a bit away and do this all over again with a new stick." He also pointed out that while he had never personally seen a bald or golden eagle carrying sticks that large, he had often seen them in nests.

Jon Gerrard expressed interest in the stick gnawing and how the eagle ended up with the small end. In his observations: " would be more common for an eagle to fly in to a limb, usually a dead limb, and break it off in flight.  Did the eagle gnaw it off at the thickest part of the limb?   If so, how did it end up holding the thin part of the limb in its talon?   Did it gnaw it part way through at the thick end, and then fly to grab the thin end and fly with it to break it off at the thick end?  And how far did it carry it before dropping the limb?" He recounted a story from the book "The Bald Eagle Haunts and Habits of a Wilderness Monarch", which he wrote with Gary Bortolotti (pages 35 and 36)

"It is of a pair of eagles nesting along the Gulf Coast of Louisiana in the 1890s.  The female regularly caught and carried Snow Geese (Blue phase) - probably weight 4.5 to 6 pounds - for up a a mile and a half to their nest.   The Geese were caught high and the eagle was able to glide down to the nest with the goose.   This feat was repeated on a number of days, and there were apparently 35 blue goose heads found in the nest, suggesting it was a common practice.    The feat was likely possible because the geese were caught high in the air and going to the nest was downhill.   Since this eagle was nesting in the southern part of the range, the female's weight would likely be in the 8 to 11 pound range, so the bird would likely have been carrying about half its weight."

Neil Rettig shared some of the observations he made filming bald eagles along the Mississippi river: "Last week I was able to get a nice shot on video of a bald Eagle near Stoddard collecting a big branch from the canopy of a cottonwood tree.  I have seen this many times.  I also filmed a juvenile bald eagle 2 winters ago catching an adult mallard in the air and having a hard time keeping it aloft. In high winds eagles can lift more, as Jim pointed out.  In winds they can hover for long periods 30 seconds or more to attack and work ducks and coots."

In general, the expert panel felt that in most circumstances, it would be unlikely for a bald eagle to carry much more than 50-60% of its body weight. However, it might carry more if the incentives and flying conditions were right: favorable winds, a down-carry versus an up-carry, a momentum capture versus a dead-lift, plenty of maneuvering and flapping space, a well-balanced load, and a highly desirable object like a large stick or a dead fawn. Jon's questions about how the Berry College female ended up with the end of the stick are very interesting when considering load balance. Did BCF end up with the thin end of the stick accidentally or on purpose? It isn't the end she gnawed.

Professor Bird provided a table from his book, The Bird Almanac, A Guide To Essential Facts and Figures of the World's Birds, which I found absolutely astonishing! According to his information, a bald eagle should be able to carry 108% of its body weight. Check out the American kestrel at 145%, the Pallas's Fish Eagle at 160%, or the tiny Calliope Hummingbird carrying its mate - 116% of its body weight!

                                        SUGGESTED WEIGHT-CARRYING CAPACITIES OF BIRDS

approx. body weight (g)*
item carried
approx. weight of item (g)
percent of body weight
House finch
cloth rag
American kestrel
Chestnut-collared longspur
Calliope hummingbird
Pallas’s fish-eagle

Bald eagle
mule deer
Golden eagle   
UID prey item
Harpy eagle
Steller’s sea-eagle

Table used permission of Professor David Bird. Taken from his book, The Bird Almanac, A Guide To Essential Facts and Figures of the World's Birds

* In all cases, a maximum weight was assigned based on the literature
SOURCES: B.P. Martin,  World Birds. (Enfield, Middlesex:  Guinness Books, 1987); J.  Terres,  ed.. The Audubon Society Encyclopedia of North American birds (New York:  Alfred A. Knopf, 1987).

Does this mean that a bald eagle can always carry 108% of its body weight?  No. But if the conditions and incentives are right, yes! The Georgia State Parks website states that bald eagles weigh 8 to 12 pounds and as watchers know, females are larger than males. So based on Bird's table, a 12-pound stick should be within her carrying capacity if the conditions are favorable.

As watchers also know, BCF dropped the stick. I would guess - and this is speculation! - that she had ideal conditions for take-off, including favorable winds, plenty of room, and a good spot for a drop. However, her load was poorly balanced. When she took off, she was carrying the stick with the heavy end up and to one side. It would have swung rapidly to hang below her, causing her to roll and pitch, and decreasing her lift. Sudden center of gravity changes are never a good thing, especially when the object you are flying with could weigh more than you do! She may have dropped the stick in response, or it could have torn itself from her grasp given its momentum. Either way, it was something to see!

Thanks so much to Jim Grier , Chuck Sindelar, Jon Gerrard, David Bird, Brett Mandernack, and Neil Rettig for talking to me! I feel very honored to learn from such accomplished and intelligent people. Any mistakes in the information presented here are mine. Brett also had some interesting thoughts on eagle vision and night flight that I am saving for another blog.

A few links - some for learning and some for fun!

Saturday, November 07, 2015

Why do birds have white poop?

This video of Mom voiding made me think about bird poop. I used to think that defecation and excretion were two words for same thing. Poop is excrement, right? But I was wrong. Defecation is the discharging of waste that was once food. Excretion is the discharging of waste created by metabolic processes - biochemical reactions that take place within living cells to maintain life. We are all familiar with the basic chain of events, which goes something like this. An eagle catches a fish and eats it. The bits of fish move from the eagle's esophagus into an expandable storage pouch called the crop, which allows birds to gorge food much faster than they can digest it. From the crop, food trickles from into the true stomach and the gizzard, a muscular stomach that uses grit to grind the fish bits into even smaller pieces. Nutrients are absorbed in the eagle's small intestine and put to work in its cells, where they assist in growing new cells, maintaining existing cells, and manufacturing the products an eagle's body needs to stay healthy.

Like food digestion, cellular processes create waste products that need to be removed from the body. In particular, humans get rid of excess nitrogen by combining it with other molecules to form urea. However, water is required to dissolve urea in urine. That isn't a problem for us, but it is for birds. Embryonic birds can't dissolve waste in water and expel it through an eggshell. Altricial nestling birds can't access water in the nest. Many birds (and presumably bird ancestors) live in or spend long amounts of time in areas that don't have adequate drinking water - think of migrants like the arctic tern, or resident birds like the emperor penguin. And water is also heavy. One ounce of water weighs 28 grams. That's a lot of weight for a bird like the ruby-crowned kinglet, which weighs just five to ten grams. Us adult human types are are supposed to drink eight 16-ounce glasses of water a day, which equals .987 pounds - far heavier than the transmitters we put on D1, D14, Indy, and Four.

So what do birds do to get rid of nitrogen? They bind it with uric acid. In humans, excretion via urea usually creates transparent clear to yellow pee (see this link for more information about the other colors pee can come in). In birds, excretion via uric acid creates the pasty white part of bird 'poop'. It takes more energy to synthesize uric acid, but that isn't as important as removing water for animals that live like birds do.

 So how about the black part of bird poop? It is feces, which are removed from a bird's body much like they are removed from ours. However, birds are monotremes - that is, their intestinal, urinary, and reproductive systems all terminate in a single posterior orifice called the cloaca, derived from the Latin word for sewer. Pasty white bird urine and feces aren't the same thing, but they both exit from the same place, sometimes at the same time, and sometimes quite explosively!

It is interesting to speculate that birds developed as they did in part because they don't need water for excretion. While large birds might be able to carry the extra weight, it seems unlikely we would have small birds given that water is heavy. We probably wouldn't have birds that migrate across or live in extremely dry places like the antarctic, the world's deserts, or the world's oceans. And altricial birds would have had to have solved the problem of getting water to nestlings or they wouldn't have survived. I will try to be more grateful for bird excrement the next time I am washing it from my car.

Things that helped me learn and write about this article:

Sunday, November 01, 2015

Spooky (and not-so-spooky) birds in folklore and tradition

One is lucky, two is lucky, three is health, four is wealth, five sickness and six death.

The ways in which we watch and learn about birds - HD cameras, high-powered spotting scopes and lenses, and DNA analyzers - are new, but our interest in them is very old. Folklore and legends about birds exist in almost every human culture. Birds and bird-like creatures have been regarded as gods (Egypt's Horus and many Native American tribes), symbols of authority (Zeus's eagle), supernaturally wise (Athena's owl and crows and ravens in general), and harbingers of death and the dead. They are found in many sacred texts, including the Bible, the Torah, the Qur'an, the Bhagavad-gita, and countless oral traditions. To watchers who didn't have the benefit of global knowledge or a scientific framework, the fascinating and sometimes eerie lives of birds could be explained only through supernatural events or powers. Our respect and love for birds has traditionally been tempered with apprehension, since the knowledge they possess could be turned against us.

We hope you enjoy this quick round-up of bird folklore. Happy Halloween!

Birds as harbingers of death
It is hard to believe that a bird could be considered a harbinger of death. But in a great deal of traditional lore, birds fly between earth and heaven or earth and the realms of the dead. As a consequence, some birds became associated with death and the dead, especially dark birds, nocturnal birds, and birds with an eerie or mournful cry. Depending on where you are from, your relatives may have known that:
  • If a bird flies into your house, there will soon be a death in the family. One of the surer omens of death is a bird entering the bedroom of a sick person and landing on the bedpost.
  • A white bird or a crow flying against a window at night foretells of a death in the house within a year. A pigeon flying against the window is a sign of death.
  • Seeing six crows is a sign of coming death, as is a whippoorwill singing near the house.
  • Seeing two turtle doves together in a tree means death is coming. If a sparrow attacks a swallow and throws it from its nest (on or near a home), a son will be born and a daughter will die.
  • A woodpecker knocking on the house is a death omen.
  • A peacock feather brought into the house is taunting death.
  • If you walk under a tree in the evening and an owl hoots right above your head, it means a relative or friend of yours will die within a year.
  • If an owl hoots while perched on your rooftop, death will pay a visit. Other parts of the world say that an owl simply hooting in the neighborhood is foreshadowing death nearby.
  • To hear a rooster crow at your door is a sign of death.
Birds as omens and talismans
In addition to death, birds might indicate future events or serve as intermediaries between the natural and supernatural world. Crows and ravens in particular have a large body of lore associated with them. Some cultures see them as essentially beneficial, although full of mischief, while others mistrust and fear them.
  • In Christian tradition ravens were believed to have special taste for criminals, and to enjoy plucking out the eyes of sinners, although they also fed sacred hermits and were used by Jesus as an example of God's provenance. In the Qur'an, a raven is mentioned as the creature who taught Cain how to bury his murdered brother. In the Talmud, the raven is described as having been only one of three beings on Noah's Ark that copulated during the flood and so was punished. North American and Canadian mythology depicts the raven as a Creator, a rascal, or a trickster. Raven created the world and saved all of the animals from a big flood, but he also created a great deal of trouble among humans for his own amusement...and we have Raven to thank for mosquitoes.
  • In Southeast Asia, a crow flying low across one's path as one starts on an important errand or trip is considered an omen, interpreted as favorable or not depending on the direction it crosses.
  • Ancient Greeks believed that if a single crow appeared at a wedding breakfast, there would be a divorce. 
  • In Sweden, ravens were known as the ghosts of murdered people.
  • A destroyed crow’s nest indicates a fire in the area within three days. 
  • If a crow lands on a house and caws sorrowfully, a calamity is sure to befall it. If, on the other hand, his joyful “carrow” is heard, it is a sign of good luck. 
Ravens and crows are not the only birds associated with luck.
  • It is unlucky to kill a robin or a swallow. Swallows have been considered sacred because they were thought to have flown around the cross of Calvary. In some places, the ill luck from an accidental killing of a robin or swallow can be canceled if burial is given to the creature. The poem 'The Funeral of Cock-Robin' refers to this tradition in a funny way.
  • In England, the stonechat is believed to be continually chatting with the Devil. In parts of the British Isles the chicken is also thought of as a bird of ill omen, due to an old idea that he “crowed for joy” at the hour of crucifixion.
  • In Norway, those in search of a drowned body would row around the body of water with a rooster aboard, believing that the bird would crow when the boat reached the spot where the corpse was. 
  • In Ireland, sparrows, stares and plovers are thought to be on friendly terms with the fairies. The lark and swallow are both birds of good omen, as long as the swallow does not rest on the housetop. 
  • In France, there was once a belief that the quail could foretell the price of wheat with the number of his calls, prompting it to be called the “Bird of Prophecy”. 
  • An American superstition holds that to possess the feathers of a peacock in your home is unlucky.
  • In Poland, it was believed that girls who died unmarried turned into doves, while those who died married turned into owls. It was also believed that owls did not come out during the day because they were so beautiful and would be mobbed by other birds out of jealousy.
Do you feed or provide water for birds? If not, the dead might be hearing about your bad behavior! 
In parts of Turkey, small vessels of water are sometimes placed upon graves for the birds to drink. Some marble tombs have basins for water as well, as birds are thought to carry messages about the living to the dead. The water is left as an attempt to curry the favor of the birds, so that the dead do not receive unfavorable messages. So get out there and fill those feeders!

Things that helped me learn and write about this subject:

Saturday, October 17, 2015

Where do falcons and eagles go in winter?

Lately I've been getting asked where our falcons go to winter. The answer is complex. Birds do not fly south simply to escape the cold. Snow and ice seal the food supply and/or habitat of many birds away until spring: hummingbirds don't have flowers, waterfowl don't have water, and most insectivores don't have insects. However, peregrine falcons and bald eagles are able to weather winter since their food supply remains locally abundant, or at least present, year-round. Both species are partial migrators: that is, some birds migrate and others don't.

Bald eagles eat a wide variety of food, including other birds, mammals, reptiles, and invertebrates. They take their food live, freshly killed, frozen and left in the nest, or as carrion, and they can gorge food quickly and fast for days if need be. Peregrine falcons eat almost solely other birds they catch in flight, but many birds winter in Minnesota and Iowa, especially in cities and along open stretches of water. While there has historically been some natural open water along the Mississippi river during the winter (Eagle Valley, for example), the number of open water spots has increased with industrialization. Power plants discharge warm water that keeps stretches of rivers and lakes ice-free, providing spots for birds like swans and geese to winter (especially when people feed them, as they do here). Cities and industrial sites provide food and shelter for non-migratory birds like rock doves, which builds populations and makes wintering in place much easier. Even in the harshest winter, falcons and eagles have ample access to food in places like Minneapolis, St. Paul, Bayport, Decorah, Red Wing, and even northerly Duluth. 

Even with ample access to food, our winter weather is pretty gnarly. Birds have wings, so why don't they leave? We don't know for sure, but we do know that migration is costly and risky, and a good territory is hard to find. Falcons and eagles that stay on site have an advantage against territorial interlopers and are less likely to find themselves replaced by another mate come springtime. Years of occupancy on site yield a deep map of the the territory - places to find food, niches to shelter, and a knowledge of the local fauna - that helps animals survive even under adverse conditions (see this blog for more information about how eagles handle winter). 

So I've talked about peregrines and eagles that stay, but what about peregrines and eagles that leave? Transmitter studies indicate that mates don't migrate or spend time together off their breeding grounds. Among falcons and eagles, young don't migrate with parents, and we don't think they spend much time together after they disperse. 

Bald eagles tolerate - maybe even like? - cold. Many eagles that migrate don't fly into latitudes free of ice and snow. Eagles in central Canada might shift south as far as the Mississippi river in Minnesota, Iowa, and Wisconsin. Alaskan eagles go west to the sea. Eagles in central north America might fly to an open body of water not too distant from their breeding grounds, joining winter eagle congregations in places like Eagle Valley, Wisconsin; Clinton, Iowa (Eagle Point Park); Bayport, Minnesota (south of Xcel Energy's Allen S. King plant); and many other places.

Peregrine Falcon Migration Map
Peregrine falcons have been documented traveling a bit further south. We've had band returns from south Florida, an oil rig in the Gulf of Mexico, and Costa Rica (click these links to read about Island Girl and Immaculata). Thousands of Tundra peregrines have been trapped and banded at the Padre Islands in south Texas as they fly from an area up above the arctic circle to Central and South America - a distance of up to 15,500 miles! Florida reported a world record number of migrating peregrines just last week - an amazing 1506 in a single day count! 

In short, migratory eagles from Minnesota, Iowa, and Wisconsin might easily be wintering fairly close to home, spending time on open stretches of water along large rivers with eagles from central Canada who flew several hundred or a few thousand miles to get there. D1, D14, and Four all wintered in NE Iowa and (in D1's case) SE Minnesota (explore the cluster map for details). However, peregrine falcons from the same area might fly thousands of miles south to warm their feathers in Central and South America before returning to our area in late February and early March. 

The whole question of photoperiod length becomes even more interesting when migration is factored in. In late February, our latitude gets around 11 hours of sunlight daily. We peak on June 21, at 15 hours, 36 minutes. Non-migratory birds and Canadian migrants to our area also experience the shortest day, at 8 hours and 46 minutes on December 21. Falcons that migrate to Costa Rica experience a different photo-year than their non-migratory counterparts, however. A falcon that left on October 1 has a shortest day-length of around 11 hours. Its days will get slightly longer as it wings south. The shortest day in October in Costa Rica is 11 hours and 46 minutes long. The shortest day of the year is 11 hours and 32 minutes long. These birds have more average daylight over the course of the year, and a much flatter photo period map during the time they spend near the equator. The difference is even greater for birds like the Tundrius falcon, which summers at and above the arctic circle.

Some things that helped me write this post: 

Wednesday, September 30, 2015

The Importance Of Lead-Free Hunting

Lead Poisoned Bald Eagle from Postville, IA
The paper A Global Update of Lead Poisoning in Terrestrial Birds from Ammunition Sources states that lead poisoning in wildfowl and waders from the ingestion of spent lead gunshot has been extensively studied, documented and reviewed over the last half century. They identify two main routes of ingestion: direct ingestion of lead pellets, which look like grit or small seeds, and secondary poisoning among birds that prey upon or scavenge animals that have been shot: primarily raptors, including eagles, hawks, falcons, and condors. Lead poisoning has been documented in 63 species of birds since 1939, including ravens, pheasants and other game birds, owls, rails, gulls, buzzards, kites, eagles, vultures, condors, falcons, red-tailed hawks, white-throated sparrows, yellow-rumped warblers, and solitary vireos. 

How serious is lead poisoning? It is both is pretty serious and very preventable.  Saving Our Avian Resources has done a lot of advocacy for non-toxic shot and they have wonderful information on their website. A few figures that struck me:
  • A study of causes of mortality in eagles submitted to the National Wildlife Health Center between 1975 and 2013 found that trauma and poisonings (including lead poisoning) were the leading causes of death for bald eagles throughout the study period. 
  • 56% of all eagles admitted to Iowa rehabilitators between 2004 and 2008 had abnormal lead levels in their blood. This ranged from a low of 37.5% in 2004 (with 62.5% of eagles being tested) to a high of 70.0% in 2005 (with 90.0% being tested). 
  • The University of Minnesota’s Raptor Center in St. Paul received 117 lead-poisoned bald eagles during the winter of 2009. In 2012, Dr. Pat Redig co-authored this paper about spent ammunition and lead poisoning in bald eagles.
  • In Canada and the USA, approximately 10–15% of recorded post-fledging mortality in Bald and Golden Eagles was attributed to the ingestion of lead shot from prey animals (Scheuhammer and Norris 1996). Elliott et al. (1992) found that 14% of 294 sick, injured. or dead Bald Eagles in British Columbia (1988 to 1991) were lead-poisoned and an additional 23% sub-clinically exposed.
  • A 2012 study by a team at the University of California at Santa Cruz found that 30 percent of blood samples taken from condors each year showed levels of lead high enough to cause significant health problems and that 20 percent of the free-flying birds required treatment to remove lead. From 1992 to 2012, the cause of death was established for 123 condors in California, Arizona and Baja California, Mexico; lead was responsible for 42 of the mortalities (
  • While lead poisoning can kill directly, lead toxicity is also a factor in collision deaths and injuries. According to the Raptor Center, about 85% of eagles that come in with collision injuries also have elevated lead levels. This video from the UK shows the effects of lead on a duck's coordination and motor skills:
Where is the lead coming from? Study after study identifies lead shot as the primary source for lead exposure.  In 1991, the US Fish and Wildlife Service banned lead shot in waterfowl hunting, although it can still be used for some other types of hunting, depending on your state's laws and regulations. A survey of ducks on the Mississippi Flyway found that the ban on lead shot reduced lead poisoning deaths of Mississippi Flyway mallards by 64 percent, while overall ingestion of toxic pellets declined by 78 percent over previous levels. By significantly reducing lead shot ingestion in waterfowl, the ban prevented the lead poisoning deaths of approximately 1.4 million ducks in the 1997 fall flight of 90 million ducks. 

Did the ban on lead shot prevent successful waterfowl hunting? No. The total number of geese and ducks harvested nationwide declined steeply beginning in about 1984, but started rising again in roughly 1992, as shown by this chart: the use of non-toxic shot did not negatively impact waterfowl hunting, but did prevent ducks, geese, and many other animals from coming into contact with lead shot by ingesting it directly or feeding on lead-poisoned animals or carcasses containing shot. 

Back in 2013, Bob picked up an eagle that died of lead poisoning shortly after he got it. At the time, he said: “I have reached a point regarding these lead poisoned eagles that surprises me.  I do not get hardened and begin acceptance for picking up these sick eagles on the verge of death and clearly in severe pain.  To look at an adult bald eagle gasping for breath and making what can only be described as cries of pain; is something that never gets easy and to think it is clearly preventable.” 

If you hunt or shoot, please use non-toxic shot. It does your prey well, it does you well, and it does the environment well. We aren’t anti-hunting and we aren’t anti-gun, but handling lead-poisoned eagles has made us anti-lead shot!

Looking for loads? Try these links:
Are non-toxic loads effective? Some resources that conclude they are:
Has reducing lead shot helped birds? In addition to this study on waterfowl, a voluntary program in Arizona and Utah appears to be reducing condor deaths in those two states.  We are looking forward to hearing the results from California, which is beginning to phase in a lead shot ban just this year.

Looking for non-toxic advocates or educational materials? Try these links:
Good luck with your lead-free hunt! 


Wednesday, September 09, 2015

Update from Decorah

Answers to your four most commonly asked questions, plus a bonus photo at the bottom of the page!

When will Mom and Dad start working on a new nest?
Did someone mention Eagle Time? In general, Mom and Dad start working on their nest sometime in October. Robin spotted Mom near N2B at one point, but I doubt we'll know whether or not they will adopt it for a month or so. For a time-lapse of the nest, check out this video, pieced together from October 2014 through January 2015: While nest work started in late October, it didn't really kick into gear until maybe mid-November.

Note added on October 10: Mom and Dad have started working on the nest. Visit our youtube channel for more:

What triggers Mom and Dad to start working on the nest? 
I've got a blog on this subject here: The short version? Two ideas: Daylight length is quite similar in mid-February and mid-October, which might encourage bonding activities in the photorefractory period that echo those in the photosensitive period, especially between territorial mates.

The eagles might be impacted by Zugunruhe (migratory restlessness, which is also influenced by daylight length). Mom and Dad don't migrate, but many eagles do. Perhaps the suite of behaviors and hormones that direct migration in some birds influences our eagles to return to nest-building.

Where are the Tree Amigos?
Given that no one has seen them, D21, D22, and D23 have most likely dispersed. D1 dispersed on August 13, 2011. D14 left twice, once on September 5th and for good on September 22, 2012. Four was a bit of an outlier. She took two longer exploratory flights in October 2014 before leaving for good on October 25. You can look at the flight maps of all three here: or explore Four's last month in Decorah here:

What's this about HD cameras?
It's true - we are moving to high definition! Cameras will be installed or replaced at N2B and N1 later this fall. Watch for announcements in early October!

Four at the Carlson Pond on 9/9/2014
Who is the eagle in this photo?
On this date in 2014, Bob took this photo of Four at the Carlson pond about a mile from the hatchery. This was one of her first 'long' flights and raised our hopes that she might disperse - which she eventually did, although she waited until late October to do so. Look for more 'on this date' photos as we wait to see what the eagles decide to do!