Wednesday, November 22, 2017

A Reflection and a Thanksgiving

Tomorrow, November 23rd, would be Bob Anderson's birthday. I assume that our friend and founder would finally have achieved his dream of retirement - or at least semi-retirement - and be busy with a book by now. Given the thankful nature of the season, it seems like a good time to take stock of where the Raptor Resource Project has been, where it plans on going, and what I have to be thankful for.

For those of you who don't know, Bob founded the Raptor Resource Project to propagate and release peregrine falcons. He was the first person to successfully breed peregrine falcons in Minnesota. MF-1, one of the first falcons he produced and released, became the first returned falcon to breed in the mid-continent following the species' extirpation in the mid-1960's. It took an incredible amount of work to keep the peregrine falcon from joining the long list of species that will be mourned on the remembrance day for lost species. I am thankful that the peregrine falcon is still with us. Where we have a will, we have a way.

Falcon MF-1. Produced by Bob, she was the first falcon to return and breed in the wild mid-continent. 
I am thankful to have met Bob. He responded to an ad my little writing business was running back in 1994. I began by writing grants, but very quickly moved into field work. Did I want to attend a banding and take pictures? Yes! Did I want to hold falcons? Yes! Did I want to rappel? Yes yes yes! The writer William Least Heat Moon said in the Wonsevu chapter of the book PrairyErth that "I'm not sure what to make of it, but I think a dream can set you on another path." Bob's dream of restoring the peregrine falcon set many people's lives on another path.

Most of the power plant people originally involved in our utility-peregrine program have retired, but a new generation of men and women have replaced them in this unique marriage of industry and conservation. The peregrine would not be where it is today without their help and whole-hearted involvement in the program. Together we've put up nest boxes and internet cameras, cared for falcons, eagles, and kestrels, and looked at ways to make generation and distribution safer for our birds. I am thankful to have worked with the fine men and women employed at America's power plants. The utility-peregrine program is an example of the ways in which humans can support wildlife even in the unlikeliest of areas. You guys are awesome...and great fun, too!

Banding at Xcel's Allen S. King plant in 2010
Bob was also working on his cliff release project. Back in 1994, he began to believe that nest-site imprinting was preventing the crossover of peregrines from power plants to cliffs. The Iowa DNR was very interested in working with Bob, so he picked up lock, stock, and barrel to move down to Bluffton, Iowa in 1996. He did a successful pilot release on the Upper Iowa river in 1997 and released a total of 19 falcons from Hanging Rock at Effigy Mounds National Monument in 1998 and 1999. The Upper Iowa hackbox can still be seen from the river, although the Effigy Mounds hackboxes are long gone. In 2000, our cliff-released falcons became the first falcons to return to the cliffs of the Mississippi. I remember going to see them quite well, since I was very pregnant with my last son. I did a lot of crazy things for and with Bob, but the only time I remember him being really worried about me was just after I huffed and puffed my way up the back of Queen's Bluff. Pat Schlarbaum's story about peregrine recovery includes information about our cliff releases. It can be read here: I am thankful to have played a small piece in this story, and very grateful to the men and women of the Iowa DNR who supported Bob's work.

Falcons raised for cliff release, 1997
In 2006 and 2007, Bob was working with Neil Rettig on the movie American Bald Eagle. After the two wrapped up, Bob said "Wouldn't it be fun to put this nest on the internet?" We made Bob's dream a reality in 2009, when the Decorah Eagle Cam uploaded an image to Xcel Energy's website every two minutes. In 2010, Luther College hosted a live feed. In 2011, we moved to Ustream and the Decorah eagles became a worldwide sensation. While we celebrated the eagles, Bob also mourned the loss of his dear friend and fellow falconer Rob MacIntyre, the 'mad scientist' who was featured so prominently in the movie RaptorForce. Rob did a lot of the work on our earlier cam systems, and his death was a real blow both personally and professionally. I am thankful to have known him and his wonderful wife Jan. They brightened every room they entered.

Rob and Bob
While Bob never lost his drive to recover birds of prey, he suddenly had a new focus. He was deeply engaged in using our bird cams to reach learners and provide a palliative window to the outside for ill, injured, and bedridden people. Online education became a major focus, but cameras still needed to be researched and purchased, and HD was increasingly looking like the next step. Enter John Howe! John began working with Bob to research cameras and camera technologies, including solar/wireless technologies (Rob installed our first solar/wireless system back in 2003) and HD. The longer Bob worked with John, the more he was impressed. Shortly before Bob's death, he let us all know that John was to follow him as Director of the Raptor Resource Project.
John and Bob
This brings us up to the present. In the two years since Bob's death, John has worked diligently to keep up with camera and streaming technology, deploy cameras, expand our online educational offerings, honor Bob's legacy, and secure funding (an organization doesn't run very long without money). He has more than proven himself as a director and a leader. I am thankful for John Howe and only wish that Bob was here to see the positive change that John has brought to the Raptor Resource Project.

So where do we go from here? We are sustained by our mission: to preserve and strengthen raptor populations, expand participation in raptor preservation, and help foster the next generation of preservationists. We follow our vision: to deepen the connection between people and the natural world, bringing benefits to both.

  • Education: We started a dedicated ad-free educational video stream and chat last year. Over 900 educators and classrooms participated in it last year, and we're hoping to double that in 2018. We also started a research and educational banding station in partnership with Luther College, began filming with the Untamed Science crew, and are planning to add a new kestrel live stream in partnership with Neil Rettig Productions and Cornell University. 
  • Preserving and Strengthening Raptor Populations: We will continue to monitor our nests, band falcons, consult on nestboxes and habitat for a variety of species, provide input on conservation issues, and work with federal and state wildlife agencies to benefit of birds of prey. We are also looking at ways to strengthen existing partnerships and build new ones. How can we connect our passionate followers with organizations looking for volunteers? How can we work closer with our utility and industry partners on providing or improving habitat for the many birds that nest on or use utility land and water in other ways? How can we advocate for birds of prey? We have done a lot, but we can do more. We stand on the shoulders of giants!
  • Fostering the Next Generation of Preservationists: We've begun an educational endowment in Bob's honor. Please follow this link to learn more and to donate! 
  • Connecting People with the Natural World: John upped the ante on our cameras! We are currently providing top-notch, HD, ads-free streams through Explore, and the opportunity for live chat through Ustream. John's current camera installations are also letting us take a look at life outside our nests - an important part of understanding and caring for the eagles and falcons we watch. A challenge for me: how do we develop quantifiable data from the thousands of hours of footage and anecdotes we've collected? Our knowledge has already changed since we first began watching the eagles (remember eagles are always monogamous?), but there is so much more to learn! 

So what else am I thankful for?

  • I am thankful for our amazing volunteers. In addition to your incredible work, my life is better for having known you. I've said it before and I'll say it again...your work makes us the best site on the web!
  • I am thankful for fans of the Decorah eagles and our other birds. Please, keep emailing and mailing your stories and art. You have deepened our lives an immeasurable amount.
  • I am thankful to our Board for providing direction and guidance. 
  • I am thankful for an unexpected and unlooked for gift: the honor to be part of the Raptor Resource Project's work. My 1994 self - I was 28 years old! - had no way of knowing what saying 'Yes' to Bob's first request would lead to. Bob, we will remember and celebrate you until we join you.

Thank you, everyone. I'm going to close with a link to a favorite blog I did on Bob back in 2012: Watching Bald Eagles. In re-reading it, I affirmed my own goal to help our eagles' futures stretch as long as their past. May Mom and Dad's progeny survive into a beautiful future, and may falcon MF-1 have thousands more descendants! Long may they all fly!

The Raptor Resource Project wishes you and yours a very Happy Thanksgiving!

Friday, November 17, 2017

Eagle eyes!

Has anyone ever called you eagle-eyed? Relative to humans, bald eagles have larger, sharper eyes that see further, collect more details, and produce stereoscopic vision to greatly improve depth perception.

A bald eagle's visual acuity begins with its eye size and shape. Dad's somewhat tubular eyes occupy over 50% of the volume of his skull, as compared with less than 5% in us spherically-eyed human types.  He can voluntarily adjust the curvature of his large cornea and lens (we're restricted to involuntary adjustments of our relatively smaller lenses only), which lets him rapidly change focus and increases the size of images reflected on to his retina. His two-lens system functions very similarly to a pair of binoculars, letting him see small objects in great detail at a distance and changing focus quickly as he flies - extremely important when hunting for squirrels, avoiding tree limbs, and locking talons with other eagles!
Eagle Eye Versus Human Eye. See end of blog for note.
The differences don't stop there. Our retinas would die without blood vessels, which supply oxygen but also scatter light and cause blind spots or shadows since light isn't reflected through them. But Dad's retinas don't have blood vessels! A pleated structure called the pecten supplies oxygen to Dad's eyes, preventing blood vessel-related light scattering and blind spots, and leaving more room to pack in light-sensitive rods and color-sensitive cones. In short, Dad's lack of retinal blood vessels enhances his visual acuity and ability to resolve detail. Large, razor-sharp images are reflected through his cornea and lens on to a much denser, clearer field of photosensors than our retinas have. How much denser? According to Keith Bildstein, the cone density of birds of prey is roughly 5 times greater than that of human beings. Dad sees farther than us, focuses better than we can, and collects more visual information about the world around him with his HD retinas!

Not enough visual acuity for you yet? Dad has two deep foveae compared to our single shallow one.  His more densely packed and deeper central foveae function in monocular vision, while his forward facing temporal foveae function in binocular vision. A densely cone-packed trench - Helen McDonald refers to it as a sort of smeared third fovea - connects Dad's central and temporal foveae, which helps him track moving objects as he switches from one mode of vision to the other, and lets him scan the horizon without moving his head. He can also fuse images from both foveae to produce a virtual reality-like stereoscopic image, which greatly improves his depth perception and ability to lock on objects. When Dad cocks his head sideways and looks skyward with one eye, he is using his monocular vision and his central foveae to scan for movement. When he looks forward intently, he is using his binocular vision and his temporal foveae to bring whatever he's looking at into sharp focus. Watch for those behaviors in the nest!

To create a 3-D'ish stereoscopic image, click on this image to enlarge it.
Cross your eyes until a third image forms between the left and the right image.

So given that Dad's visual system combines image detectors, tracking devices, binoculars, high-definition cameras, and virtual reality headsets, how far can he see? Accounts differ, but we've watched Mr. North respond to a squirrel in his nest from 550-600 feet away with no problem at all, and we've seen eagles at both nests respond to nest intruders long before they come into our view. Sources suggest that bald eagles can resolve:
  • A 2-millimeter insect from 18 meters away
  • A mouse from 446 feet away
  • An ant from the top of a ten-story building
  • The faces of basketball players from the back of a large arena
  • A rabbit from over three miles away
As if that weren't enough, Dad also sees more colors than we do! In addition to perceiving red, green, and blue, a fourth cone allows him to see into the ultraviolet spectrum. Drops of oil in each cone selectively filter out certain colors, giving Dad greater sensitivity to different color shades and allowing him to see polarized light. These adaptations allow him to see the urine trails or prey, signal mate health, and may help him navigate as well. 

Helen McDonald states that Dr. Andy Bennett, a researcher in the field of avian vision, considers the difference between human vision and bird vision as that between black-and-white and color television. Bald eagle eyes see a world that is brighter, sharper, more colorful, and far more detailed than our own. I wish I could see like they do!

Did you know?
Bald eagles have three eyelids! Their clear nictitating membrane helps keep their eyes free of debris while they are flying. A specialized gland associated with the membrane produces an antibody (lysozyme) that helps keep their lens free of infection.

Despite these advantages, bald eagles have one big disadvantage - a blind spot directly in front of them. I was not able to find any information about the size of the spot, but it is most likely increased by their relatively prominent brows and large beaks. We've seen them hit one another - and in Dad's case, the tree trunk! - and this might also be another reason why collision-based trauma is a leading cause of death for bald and golden eagles. 

We can't see stereoscopically like bald eagles can unless we trick our eyes! You can learn more about stereoscopes here, or check out a video of images here!

Things that helped me learn and write about this topic
If you have a bird-lover in your life, I highly recommend the top two books
Note: The image of the eagle's eye that I used can be found at several websites, including However, it looks a little bit more like an owl's eye to me. Having said that, I'm not an expert and eagles and owls have fairly similar eyes, so I decided to use it.

Tuesday, November 07, 2017

When will our eagles lay eggs? Bald eagle breeding in Iowa and Florida

We're getting some questions about why the Decorah Eagles aren't laying eggs yet. Are they going to lay eggs? Will the nest be productive? The short answer is 'Yes' - the Decorah eagles historically lay eggs in February, while the Decorah North Eagles laid eggs in March in 2015, and in February in 2016. The longer answer is more complicated. If you don't want to read it, skip down to the bottom of the blog for breeding season information.

Bald eagle breeding season: not the same everywhere
We know that Bald Eagle breeding season varies by latitude. While breeding chronologies differ from nest to nest and state to state, in general:
  • In the SE United States, bald eagles may begin laying eggs in November
  • In the SW United States, bald eagles may begin laying eggs in December.
  • In the northern United States, bald eagles may begin laying eggs in mid-January.
  • In Alaska, bald eagles may begin laying eggs in late March or early April.
Bald eagles lay eggs earlier than many other diurnal raptors, or daytime birds of prey, and eagles in the southeastern US lay eggs earlier on average than their counterparts in other places. This is more unusual than it looks. Roughly speaking, a non-tropical bird's year can divided into two big parts: the photosensitive period and the photorefractory period. In the northern hemisphere, the photosensitive period starts when daylight length begins increasing after the winter solstice in late December. Birds' gonads swell and produce sex hormones, leading to productive mating and egg-laying. During the photo-refractory period, which starts after eggs are laid, birds' gonads shrink and mating becomes less frequent or stops altogether. Bald eagles in Florida are an interesting exception to this rule, since they begin laying eggs as early as November, when daylight length is still decreasing and their gonads should be (but obviously aren't) senescent. 

So why do Florida bald eagles lay eggs so early? One possibility: daylight length, especially in south Florida, is a poorer predictor of the season than it is in Decorah, Iowa. This might free the gonads of Florida eagles from the circannual light-based cycle of swelling and shrinking that regulates northern bird breeding. In Fort Myers and elsewhere in south Florida, the difference between the longest day and the shortest day is just 3 hours and 21 minutes, compared to 7 hours and 26 minutes in Decorah.

Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons must rely on cues other than daylight length to regulate their circannual clocks. So if daylight length isn't especially important in SW Florida, what is? Check out the chart below.

Annual Averages, Fort Myers, FL

Daylight length isn't a great predictor of seasons in Fort Myers, but rain sure is! And what comes with rain? Clouds! The Max Planck Institute for Ornithology suggests that equatorial (and possibly near-equatorial) birds use daytime light intensity instead of length to regulate their internal clocks and breeding cycles. Under this scenario, the rapid increase in daylight intensity that begins in early September swells SW Florida eagle gonads and begins their annual breeding season. How tightly coupled is the increase in light intensity with the onset of the breeding season? Check out this cloud cover chart from Fort Myers...
Cloud Cover Chart, Fort Myers, FL
Two things. Firstly, the cloud cover chart for Fort Myers, Florida, somewhat resembles the daylight length chart for Decorah, Iowa. Like the daylight chart, it has a steep-sided trough that shows rapidly changing light availability, even though we are measuring intensity instead of length. Secondly, the breeding cycle of eagles in SW Florida appears to be tightly coupled with light intensity. Their overall cycle is quite similar to that of northern eagles, but the external cue that fires breeding behavior appears to begin in September or October instead late December. Of course, laying eggs in November and December also allows nesting eagles along the Gulf coast to avoid the hurricane/rainy season, which runs from June 1st through November 30th, and takes advantage of seasonally available flushes of food when eaglets are at their most vulnerable. Fledglings will have two to three months to gain their wings and hone their hunting skills before light intensity drops and the rainy/hurricane season starts up again.

This results in a chicken/egg quandary for me. Gulf coast eagles appear to be responding to a change in light intensity instead of length. Given the timing of the hurricane/rainy season, it also seems very likely that laying eggs in November and December results in higher offspring survival rates among eagles along the Gulf coast. Is the difference in southwest Florida/Gulf coast breeding cycles the result of an evolutionary process over generations, or does the ability to change breeding cycles and circannular clocks quickly lie dormant in bald eagles and other organisms? This might be important to know given the weather and climate changes facing us today. We wish the best of luck to the southwest Florida eagles this year!

Important events in Decorah, Decorah North, and Fort St. Vrain
Interested in key events at the Decorah, Decorah North, and Fort St. Vrain nests? Mark your calendars as follows!
  • In the nests we watch in Iowa and Colorado, bonding and copulating behaviors become more pronounced and frequent after the winter solstice. Female eagles begin laying eggs 5-10 days after productive copulation begins. This usually happens in mid-February at all of our nests, but can change if an eagle takes a new mate. New mates often seem to push nesting chronology a little later, especially in the first year. 
  • Each egg is laid about 3-5 days apart, and incubation starts with the laying of the first egg. However, eagles may spend more time off their eggs in warmer weather. 
  • Eagle eggs begin hatching roughly 35 to 39 days after they are laid. This usually begins in late March at all of our nests. Hatch can take more than 24 hours for any given egg.
  • Eaglets spend 75-80 days in the nest before fledging. This usually happens in mid to late June at all of our nests.

Did you know?
Fledglings appear to leave the SW Florida nest in May, just as cloud cover begins increasing and light density drops. Fledglings in Decorah leave the nest area between August and mid-October, just as daylight length goes into a steep decrease. It is interesting to speculate that these behaviors are driven by the same circannual clock that drives eagle breeding biology.

Circannual clocks drive circannual rhythms, or biological rhythms that occur on an annual basis - in northern birds, think nesting and migration. But we are also driven by circadian clocks, which keep us in sync with Earth's day/night cycle. Clock genes are extremely influential, affecting the activity of most other genes in the body in one way or another. To read more about our internal clocks, try starting here: and here:

Things that helped me learn and write about this topic:

Monday, October 30, 2017

Birds in superstition and folklore

One is lucky, two is lucky, three is health, four is wealth, five sickness, and six death.
The Children's Mother Goose

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 associates and companions of deities
Rachel Warren Chad, a co-author of Birds: Myth, lore & legend, states that Deities from cultures around the world have birds associated with them. Doves (bird of Astarte, Aphrodite/Venus, Holy Spirit), ravens (Odin’s familiars in Norse mythology), cranes (sacred bird of Hermes/Mercury, Celtic bird of the moon) and eagles (familiars of Zeus/Jupiter) are among the many species assigned such roles in myth and legend.  They fly between heaven and earth, deliver messages to and from the gods, and signify divine might.

Birds are also found in Christian folklore. In Europe, birds with bright red or pink splotches (robins, crossbills, finches) were said to have been stained with Christ's blood as they attempted to pull thorns from his body or nails from his hands and feet. Another superstition states that the robin got its red breast after taking water to thirsty sinners in Hell. The sparrow gets a bad rap, since it attended the Crucifixion to encourage the guards to torture Jesus, but it's still a very bad idea to kill a sparrow or put one in a cage. Eagles are said to go into seclusion, pluck out all of their feathers, and shed their beak and talons to live longer. While not specifically Christian, this myth (it isn't true) is usually accompanied with Christian symbolism. Eagles are also considered to be one of the four dimensions of creation and a messenger of God.

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. This belief is so widespread that Snopes has a refutation:
  • 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. If you break a robin's egg, something precious to you will soon be broken.
  • 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. Magpies carry a drop of the Devil's blood under their tongues and a lone magpie loitering near your house means that the Devil is afoot and stirring up trouble!
  • 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 quail could foretell the price of wheat with the number of their calls, prompting it to be called the “Bird of Prophecy”. The ancient Romans practiced ornithomancy, a form of divination that took omens from the flights and cries of birds. If a bird cries from the north, ill luck will ensue; if from the south, a good harvest; if from the west, good luck; and if from the east, love.
  • An American superstition holds that to possess the feathers of a peacock in your home is unlucky. It is also unlucky to have peacock feathers on the stage or comprising any part of a costume, prop, or scenery!
  • 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.
  • Did a bird poop on you today? Too bad if it didn't, since Russians know that bird poop brings good luck! But it is bad luck to see an owl during the day (videos of owls don't count as far as we know).
  • If the first bird you see on Valentine’s Day is a goldfinch, it means your spouse will be rich.
  • Many birds are believed to carry dead souls or messages from the dead, including sparrows, blackbirds, ravens, swifts, and even doves. In France, the souls of unbaptized children who die are said to become birds until they gain entry to heaven. 
Do you feed or water 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 to curry favor with the birds, which prevents them from carrying unfavorable messages to dead loved ones.  So get out there and fill those feeders before it's too late!

Things that helped me learn and write about this subject:

Friday, October 27, 2017

Hunting Lead-Free

With firearm deer hunting season getting ready to start in many places in the midwest, it seemed like a good time to remind people to hunt lead-free. Our director John Howe does so, and so do many of my friends, most of whom are concerned about lead's impact on wildlife and on themselves. Ingesting lead ammunition kills Bald Eagles and other birds of prey: ingesting lead fishing tackle kills loons and other waterbirds. Lead poisoning has been documented in 63 species of birds since 1939, including eagles, ravens, pheasants and other game birds, owls, rails, gulls, buzzards, kites, vultures, condors, falcons, red-tailed hawks, white-throated sparrows, yellow-rumped warblers, and solitary vireos. If you hunt, do wildlife and your family a favor and switch to non-toxic ammo.

This video about the issue features Kay Neumann from SOAR

I've compiled some information about wildlife exposure to lead. If you are looking for places to purchase non-toxic ammo, follow this link to our website: or check out SOAR's excellent resources: If you aren't familiar with non-toxic shooting, check out this Tom Roster's 2016 non-toxic shot lethality table:

Is lead really a problem? 
Absolutely. Lead is a toxic metal with no known safe exposure levels for humans or wildlife. In the United States, an estimated 3,000 tons of lead are shot into the environment by hunting every year, another 80,000 tons are released at shooting ranges, and 4,000 tons are lost in ponds and streams as fishing lures and sinkers. As many as 20 million birds and other animals die each year from subsequent lead poisoning (yes, this shocked me, but I verified it with the source ( and

Lead is a big killer of Bald eagles. From 1975 to 2013, the National Wildlife Health Center conducted a mortality study on the carcasses of 2, 980 Bald Eagles and 1,427 Golden Eagles. Their summary looked like this:

Cause of deathBald eagleGolden eagleTotal
Drowned11 (0.4%)3 (0.2%)14 (0.3%)
Electrocution 372 (12.5%)381 (26.7%)753 (17.1%)
Emaciation176 (5.9%)90 (6.3%)266 (6.0%)
Disease155 (5.2%)39 (2.7%)194 (4.4%)
Poisoned762 (25.6%)117 (8.2%)879 (19.9%)
Shot 303 (10.2%)196 (13.7%)499 (11.3%)
Trapped59 (2.0%)39 (2.7%)98 (2.2%)
Trauma 681 (22.9%)84 (26.9%)1,065 (24.2%)
Undetermined 298 (10.0%)131 (9.2%)429 (9.7%)
Total 2,9801,4274,407

The study found that 63% of the poisoned bald eagles and 58% of the poisoned golden eagles had been killed by lead, which was the second-biggest killer of bald eagles. Note that the study did not look at whether lead was a factor in trauma deaths (the biggest killer of eagles if poisoning is broken into lead poisoning and everything else). However, other studies have found that sub-lethal amounts of lead play a large role in eagle collisions. Lead is an even bigger killer of eagles than this study indicates.

How are birds and other animals exposed to lead?
They eat it. Fish-eating birds like bald eagles and loons eat fish that have ingested lead sinkers or other tackle, while scavenging birds like bald eagles, vultures, condors, and some hawks feed on gutpiles left by hunters that contain fragments of lead ammo. They also eat the carcasses of animals that weren't recovered and eventually died of their wounds. Waterbirds like trumpeter swans, mallard ducks, and loons ingest ammunition or lead sinkers while foraging in lakes, and upland birds like pheasants mistake shot for seeds or grit and eat it.

If I switch to non-toxic ammo, will it really make a difference? 
Absolutely! Switching to non-toxic ammo will prevent lead from entering the environment, which will keep it out of the bodies of birds, animals, and people that enjoy eating wild game. Here's an example: In 1991, the U.S. Fish and Wildlife Service outlawed the use of lead ammunition to hunt migratory waterfowl after it was estimated that 2 million ducks died annually from ingesting lead pellets. A follow-up 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. Plenty of ducks were still harvested, but far fewer died accidentally after ingesting lead.

Does non-toxic ammo and fishing tackle actually work? 
No one wants to switch to ammo or tackle that doesn't work, but non-toxics work very well! Let's start with wildfowl. The total number of migratory waterfowl harvested nationwide declined steeply beginning in about 1984, but started rising again after the ban on lead ammo was enacted, as shown by the chart. Requiring 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. How about doves? A multi-year study by the Texas Parks and Wildlife Department found no statistical difference between lead and steel ammunition in terms of doves hit, missed, crippled, and killed at all ranges. How about other game, including deer? A large study done in Germany found that lead-free rifle bullets were as effective at killing wildlife as conventional lead bullets. How about deer and only deer? This article in Whitetails, the magazine of the Minnesota Deer Hunters Association, discusses non-toxic ammo with eight hunters that made the switch.

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. 
The best time to switch to lead is now! Good luck with your lead-free hunts this year!


Friday, October 20, 2017

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

The last time we blogged about prey remains from Xcel Energy's Fort St. Vrain bald eagle nest, we talked about mammals. This time, we're going to explore fish and turtles! In all, we found 35 fish remains, 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. Our aquatic remains included:
  • seventeen opercular bones (eleven left and six right, from at least twelve different fish)
  • eight preopercular bones 
  • one otolith 
  • four skull tops 
  • five skull fragments, and; 
  • three turtle shells. 
So what are opercular bones and otoliths? The operculum, which includes the preopercular and opercular bones, is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding.

The opercular series. Nine/yellow is the opercular bone. Six/red is the pre-opercular bone
Otoliths are a calcium carbonate structure in the inner ear of vertebrates. They act as gravity, balance, movement, and directional indicators in all vertebrates, and have a secondary function in sound detection in higher aquatic and terrestrial vertebrates, including fish. Vertebrates have three pairs: the astericus (Ast), lapillus (Lap), and sagitta (Sag). Many fish can be identified to genus and species by their sagittal otoliths but alas, we found only one!

At least we had several opercular bones. While we couldn't use them to determine genus and species, they could determine the size of the fish the eagles were bringing in. Several papers document a close relationship between the size of the opercular bone and the total length (from nose to tail) of the fish. I chose Hostetter and Munroe's 1993 paper Age, growth, and reproduction of Tautoga omtis, which used the formula log10 TL = 1.2916+0.860 log10 OR for males. The paper meticulously documented Hostetter and Munroe's methodology and results, which were used in subsequent studies of several fish species. It was also well-cited and required nothing more than a dial calipers, intact opercular bones, and a good calculator - three things I had on hand!

I used the dial calipers to determine Opercular radius (OR). which Hostetter and Monroe define as the distance from the articular apex center to the midpoint of the posterior margin of the opercle. It looked something like this...

Opercular and preopercular bones of our largest fish. 
I ran my measurements through the formula log10 TL = 1.2916+0.860 log10 OR to obtain the lengths below (more on that at the end of the blog). While we collected 17 bones, only 14 were intact enough to use.
ORTotal lengthNumber/side
61mm26.3" / 668.02 mm1 / left
47mm20.9" / 530.86 mm1 / left
46mm20.6" / 523.24 mm1 / right
43mm19.4" / 492.76 mm2 / both left
42mm19.0" / 482.60 mm2 / both right
41mm18.6" / 472.44 mm2 / left, right
40mm18.3" / 464.82 mm3 / left, right, left
34mm15.9" / 403.86 mm2 / both left

While I was impressed by the largest fish, it was a real outlier. The average fish size was 19.0" - a nice size at just a little over 1-1/2 feet long. So what kind of fish would they be likely to be and how heavy might they have been? I checked out a fishing report for the St. Vrain state park and emailed the Laughing Grizzly fly shop to find out! Given the size of the fish and the stretch of the river, Mike suggested either sucker or bass, with the outlier possibly belonging to a carp. Their length/weight profiles look something like this:
  • Common Carp: 16 to 26.5 inches at 2 pounds to 10 pounds
  • Largemouth Bass: 16 to 25 inches at 2.4 pounds to 9.10 pounds
  • White Sucker: 16 to 20 inches at roughly 4 to 6 pounds 
  • Longnose Sucker: 15-25 inches at 1 to 2 pounds (although Montana's field guide states that the largest can be around 5 pounds and fish of up to 7.3 pounds have been reported)
In addition to sizing fish, opercular bones can also be used to age fish. Like trees, they produce annular rings that can be counted once the bones have been cleaned and held up to a strong light. However, I was confused by the age of my fish. Almost every opercular I counted yielded an age of four or older, with several between six and nine years of age and the oldest (the outlier) about fourteen. I hadn't expected my fish to be as old or as big as they were. Was I counting wrong? What was going on?

Operculars. Mr. Big is at left. It was the oldest and the largest opercular bone.
As eagle cam watchers might recall, sucker fish rise in the spring and early summer to spawn on gravel beds and sand bars. Every year, Dad Decorah and Mr. North haul in suckers by the dozens once the run starts, sometimes bringing in more than one at a time! However, Longnose Sucker don't become sexually mature until they are between five and nine years of age, while White Sucker don't reach sexual maturity until they are three to eight years old. This means that spawning suckers are a minimum of three years old at spawning, and could easily be older. Finally, my large old bones make sense! Do we know that these fish are suckers? No - but age and size as determined by the opercular bones fit the species, especially given the presence of suckers as identified by local fishing guides, their age at sexual maturity, the amount of sand and gravel bars in the area, and the seeming preference of eagles for suckers when given the choice between suckers and, say, trout. Bob would love this, since he theorized back in 2012 that sucker fish spawning could be the Midwest's equivalent of a salmon run when it comes to protein sources for eagles and other animals that eat them. We'll be watching closely during the spawning season in 2018 to see if we can identify the fish that Ma and Pa FSV bring in! (Amy's note: There were two very distinct shapes of opercular bone, which makes me think that at least two different species were brought into the nest. One was rounded [Mr. Big and several of the others], while the other was more angular).  

Of course, fish weren't the only aquatic animal the eagles brought into the nest. We also found three turtle shells. Alan Resetar, the McCarter Collections Manager for the Chicago Field Museum's Amphibian and Reptile Collection, identified them as spiny softshells (Apalone spinifera). This was very helpful, since I originally thought they might be western painted turtles or small snapping turtles. He also provided a link to this guide for identifying turtle shells and remains: Take a look at the picture below, which clearly illustrates how the spine and ribs are fused to the shell, giving turtles their distinctive walk.

The underside of a turtle's shell 
So what did we learn? Collecting prey remains from the Fort St. Vrain nest gave us a couple of unexpected insights. As dry as the area is, aquatic animals (especially fish) are still an important part of Ma and Pa FSV's diet - something we didn't expect. The spiny softshells were a surprise, since they are at the extreme western end of their range. And like the Decorah and Decorah North eagles, the Fort St. Vrain eagles appear to take advantage of the spring sucker run, which comes at a very timely point in the lives of their young! While some specific prey details are different (prairie dogs!), the remains we found fit within the larger framework of bald eagle behavior - getting the most food for the least amount of effort and risk expanded. Benjamin Franklin famously called bald eagle behavior lazy, but it takes experience and intelligence to know where and how to find food, especially in a beautiful but unforgiving place like Colorado's Front Range.

Xcel Energy, thanks for all of your hard work and support. You are wonderful eagle and falcon friends, and I look forward to collecting prey remains from Fort St. Vrain next year! I was quite fascinated by this nest, which is much drier and 'stickier' than our Iowa nests. The lack of humidity means that materials don't tend to compost in the nest, although the eagles still prepare the area under the nest cup and strip bark from the sticks they bring in. We have three eagle nests to watch in Iowa and Colorado. What can we learn from their differences and similarities? We look forward to finding out!

Did you know?

I wish we found more otoliths, since researchers are using them to model climate impacts: I am hoping to send our fish and mammal collection to the Field Museum in Chicago!

Most of the fish we found were within the carrying capacity of Ma and Pa FSV. Under standard conditions, Bald Eagles can lift and carry around 60% of their body weight, and in some circumstances they can carry more! A link:

Things that helped me learn and write about this topic:

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!