Wednesday, March 28, 2012

Nest Roundup

It's been a busy couple of days for everyone! Here is a complete RRP nest round-up:
  • Two eaglets in Decorah. D12 hatched on 3/27/12 and D13 hatched this morning.
  • Two eaglets in Fort St. Vrain, Colorado
  • Two peregrine eggs at Great Spirit Bluff. We're waiting for one or two more.
  • Three GHO owlets in Valmont, CO. These guys are growing fast!
  • One peregrine egg at Xcel's Sherco power plant
  • Several goose eggs at EagleCrest. Hatch is anticipated between April 3 and April 7.
  • Turkey Vultures are back in Missouri, although no one has settled into the nest yet.
We have a nest calendar at that we try to keep current, although the birds sometimes get ahead of us. We maintain photo albums on our facebook page and our flickr account, and have videos on our youtube page:
If you missed D13 hatching this am, here's a video:

The Emergence of D13

Friday, March 23, 2012


This topic is a combination of numerous codes and explanations guaranteed to assist you in viewing or discussing the eagles.

With Eggstraordinary Graditude to chatters, and many other EAs who contributed to our eggspanding vocabulary of Eagle-ese / Eaglish we proudly present the Decorah Eagles Diction-Aerie for you to print out, mantle over, and devour the knowledge presented by the Fledge-U-Ating Eagle 101 Class of 2011. (Original post on Facebook by Sherri Elliott)

The Diction-Aerie
Air-obics - Extending wings and catching a bit of air.
Anthropmorphism - projecting human characteristics onto animals.
Apteria - area on breast with no feathers; aka -brood patch.
Balloon Mantle – a puffball of feathers exhibited by E3.
Beak Geeks - people that are avidly watching them daily.
Beak Lips – area of beak sides to corner of mouth.
Beakering – sibling disagreements.
Beakoff - eaglets fake fighting with their beaks.
Bedreagled Eaglets – raggedy look after bad weather.
Bird Nerds – people that are avidly watching them daily.
Bling – unidentified accoutrements brought to the nest from Nest Depot - usually brightly colored.
Branch Office – Mom & Dad spend most of their time in this space adjoining nest after eaglets grow into juvies.
Branching - eaglets hopping from one branch to another prior to fledging.
Breakfish – first meal of the day.
Cameritisi Permanentitis Bugitis – bug on camera lens, also known as camera bugs.
Cere – fleshy, membranous covering of the base of the upper mandible.
Claw Floss – name given to Pinky, the baling twine.
Cleaning Coma – behavior emulating Dad’s cleaning skills, but generally tiring quickly, lapsing into face plant.
Clown Clomp – comical eaglet first steps learning how to walk.
Clown Feet - oversized feet/talons that the eaglets haven't grown into yet, nor know what to do with.
Convocation – group of eagles in tree or on ground.
Corn Husk – outer dried corn covering coveted in nest.
Corn Husk Pillow – said item used as head rest.
Corn Stalk – building material for nest crib rails.
Clutch – number of eggs laid in a nest.
Crop - area in neck where food gathers first before entering stomach if it is full.
Crop rotation - food moving from the crop to the stomach for digestion (and filling up again).
Cuddle Huddle - all the e's close together for safety/warmth in a group.
Cuddle Puddle – horizontal E cuddle sprawl.
Decorah - the idyllic location in Iowa where our family set up its Home-Tweet-Home
Decorah Drop – nap flop.
Decorah Front Porch – our place to watch the EEeee's.
Decorah Shimmy - back and forth motion that Mom/Dad use to position themselves over the eggs/eaglets.
Decorahating – beautification of the nest.
EA'S - Eagle Addicts, aka: Eagle-holics.
E-ddicts – those who watch eaglets and stay in pajamas all day.
E-Gulp - swallowing food whole.
E-Heap – pile of eaglets.
E-Lump - same as cuddle huddle.
E-Pology - Submission bow or another act of 'sorry' after a sibling altercation.
E-Team – long suffering worrywarts who love eaglets.
Eagle Condo – eagles in penthouse, smaller birds in lower stories.
Eagle Kneivel – daredevil or showoff behavior.
Eagle Time – no time that has anything to do with human time.
Eagleholics Anonymous – 12 step recovery program for eagle addiction..
Eagleholics - (Eagle-holics) people that are avidly watching them daily.
Eaglestock/Eaglefest - 206+ million viewers united on web cam broadcast.
Eagle-ese – our unique vocabulary, also known as Eaglish.
Eagleibrium – balance achieved only by eagle walking.
Eaglemaniacs – people who eat, drink and sleep eagles, with not much real sleep actually occurring.
Eagleicious Delicious – any delightful E behavior.
Eagletecture – construction skills used by Dad to create the nest.
Eaglish - all the words we made up for this dictionary.
Eagulp – swallowing food whole.
Ealergies – involuntary sneezing reaction.
Eyas stage - fresh from nest
Face Plant - off balance eaglet plopping into nest face first, perhaps going into food coma.
Feaking - cleaning a beak.
Feathairdresser – wind redecorating Mom’s hair.
Featherline – e’s hairline feather growth giving them distinguishable identifiers.
Fish Fledge – result of food fight when intended meal accidently goes off the nestbowl.
Fishereagle – Dad, Dad, Dad.
Flappathon – endurance contest of e’s getting pumped up.
Fledge – taking the leap from branches to the air of the big beyond.
Fledge Fest – gathering of EA’s making road trips to witness fledging.
Fly-By – parent checking in, but not landing, and with or without food.
Fly-By-Fake-Out - parent flying by with food to lure E's out of nest.
Flying monkeys – teenlets similarity when wingersizing to the Wizard of Oz flying army. Hum the song: oh weeee oh...ohhhh oh when seeing this behavior.
Food Coma - state of suspension E's go into after eating too much.
Fret of chatters - a group of chatters worried about the eagles.
Flapadoodle: Amusing flurry of wing flaps performed by Mom, sometimes Dad, while sitting (incubating) the eggs. Generally occurs in middle of night and scares the heck out of everyone watching.
Flapping Jacks - eaglets exercizing their wings.
Fledge-U-Ation – eaglets graduate to fledging.
Fritching - itching new emerging feathers.
Gnat – larger than noseeums and especially fond of the eagle's head area resulting in eagle neck jerk twitching.
Gnat Gnat – a term of endearment used interchangingely for nite nite by EAs.
Gnat Scat Boogie – the e’s headtwich dance.
Guy-liner – one way to identify Dad is black liner around his eyes.
Hallux – rear locking talon, also known as eagle thumb.
Hard Penned – feathers firmly attached to bone.
Hoppersizing – up and down movement, usually in conjunction with wingersizing.
Hop-Squash – exhuberent nest hop resulting in a sibling step on. Usually E2 gets hop-squashed.
Hoppiness – what else would you do after a good feed and found you had wings? Happy-Hop!
Hover Mantle – mantling behavior parallel to the prey of the day.
Hovering – catching air with outspread wings while staying in a fluttering suspended motion.
Hugbrella – wingstretch from one e to another.
Kettle - group of eagles in the air.
Juvie sprawl – juveniles taking up extra nest space spreading wings out while napping.
Leap Eagle – hopping over a sibling.
LEGO Eagle – pixilated image of our eagles.
Lumpasizing - E's staying close together or sleeping in a pile.
M.O.D.S – Master Ornithological Data Searchers; also gatekeepers of the RRP FB page or chat.
Mantle - The action of a bird spreading its wings, fanning the tail & arching over prey, to hide it from other predators, including other birds or siblings. From Old English/Norse for cloak. (E3 delighted us with several distinct mantles: Balloon Mantle and Ninja Mantle).
Master Mantler – E3 showed extraordinary mantle diversity.
nest depot - nearby areas where corn husks, branches, horse hair, or nesting material is available.
Moist Fowlettes – wet eaglets.
Mombrella – Mom covering her eaglets with her wings, mostly in inclimate weather. (see also poptent).
Moonwalk – backup walk prior to a poop shoot.
Muskrat jerky – poor thing which gets picked on by the e’s w qhen unearthed from the nest.
Nare – nostril holes on the beak.
Nest Depot – wherever Mom & Dad can find new d├ęcor for the nest; ie- horsehair, corn husks, branches, straw.
Nest guests – anyone watching the UStream video.
Nest Potatoes – eagles lazily lounging, usually after eating.
Nestication – staying put in nest or branches; too relaxed to pack and fly off.
Nestogarbage – nest garbage or debris.
Nestoration - The act of rearranging or redecorating the nest
Nestovers – uneaten food found in the nest.
Netiquette – a level of decorum expected on Decorah’s RRP Facebook page.
Nictitating Membrane – transparent inner eyelid, also known as the third eyelid protecting the eye.
Numb Butt – affliction caused by sitting at the computer too long.
Ninja Mantle – heightened Zen-Like state of mantle & hover (first exhibited by E3 on 5-29-11)
Obstacle Occlusion – varying perspectives of the reality of the nest.
Outstinkt - eaglets knowing instinctively to PS out of the nest.
Owl – urban legendary creature purported tohave attacked eagle nest; totally mythical.
Pffffftt! – the distinct sound coming from a PS.
PS - poop shoot - evacuation of the bowels.
Pancake – flat eagle in sleeping position.
Pet Pillow - using your sibling as something to rest a part of your body on.
Pinky – name given to pink/red bailing twine brought into the nest, that inadvertently wound around E2’s foot.
Piscivore - fish eater.
Poop Art - original whitewash gouache on the nearby trees; a takeoff of the 1960’s Pop Art Movement.
Poopcassio - PS artist.
Poptent - Dad standing over the chicks with wings spread keeping them safe from snow/rain/wind or predator.
Porch Peeps - The E's adoring EA's who sit on an evereggspanding porch overlooking the beloved cottonwood tree to pay homage to our eagles.
Post D-Epartum Depression – condition to what will happen to EA’s when eagles leave the nest.
Predicure - manicure for a predator.
Prey Buffet - whatever the parents happened to bring for dinner.
Prey Toy – meal tidbit used as plaything.
PSFS – print screen finger syndrome synonymous with copy, print and save web stream photo captures.
RWS - restless wing syndrome.
Ramage - true feathers coming in.
Raptor – a bird of prey, regal in the birddom. (Latin, one who seizes, from rapere).
Reversed Sexual Dimorphism – the female eagle is generally bigger than the male – opposite of other species.
Rictus - wide open mouth.
Screech-fest - sound associated with food fest.
Screagling – screeches made by e’s.
Screeeeeeee – typed sound the e’s make in one or multiple vocalizations; can interchange with squeeeeee.
Screaching – sound associated with food frenzy.
Separation eagxiety – the anxiety tht the last eaglet feels when it is left in the nest alone, sans siblings.
Shaking Juvie Syndrome – trying to get the gnats off ones head by shaking it.
Spicules – the rear talon.
Sprawled Eagle – eaglet sleeping with wings spread covering a larger mass area than spread eagle.
Spread Eagle - eaglet sleeping with wings spread (see also sprawled eagle).
Squabbit – what we call the newest furry snack when we can’t figure out if it is a squirrel or a wabbit.
StarBeaks – EA’s favorite corporate cawfee. Most popular blends: Decorah Decaf and Mocha Mantle.
Sub-Adult - juvenile eagle.
Sweagle Dreams – sweet eagle dreams.
Syrinx – flap between esophagus and lungs that eagles make vocalization sounds.
Tail Wiggle-Waggle – movement of the eaglets tail after they realized they had one.
Tarsus – the section of vertebrate foot between the leg and metarsus.
Tippytalon – eaglets doing the ballerina thing.
Tweagles – juvenile teen eagles.
Tween Preen – Eaglets in their ‘awkward’ phase trying to get their feathers unfurled.
Twiggs - playing with branches like Lincoln logs.
Twittering - calls made by young eaglets.
U.I.A. – unidentified animal brought in as prey.
Whatta - The best way to start a sentence!
Wilson – name given to the beloved cornhusk that resembled the volleyball in the film “Castaway”.
Windteruption - high wind day that causes the e's to lay low.
Wingercizing - excercizing the wings.
Wingpits – self explanatory.
Wing Smackdown – exhuberent wingersizing between two or more eagles resulting in a takedown.
Wing Whack - one eaglet stretching his wing while laying down and hitting his/her nearby sibling with it.
Wonderstruck - The overwhelming feeling produced by the EEeee's.

Alpha Codes
A = Ant
AD = Additive
B = Bugs
BB = Beak Biting
BH = Branch
BFP = Big Front Porch
BG = Beak Geeks
C = Cat
CA = Camera
CH = Cornhusk
CHP = Corn Husk Pillow
CL = Clutch
CP = Crop
CS = Cornstalk
CT = Cottonwood
D = Dad, Daddy
D1 = Dog (This was prior to D1, being named D1)
DE = Decorah
E = Eagle or Eagles (1,2,3)
EA = Eagleholics Anonymous
EG = Egg
EPU = Eagle Parental Unit
E101 = Eagleholics 101
E-lumni = Eagleholics 101 Graduates
F = Fledglings
FS = Fish
FC = Food Chain
FP = Faceplant
G = Gnats
GR = Grunt
H = Horse
H1 = Human 1, Human 2 (at farmhouse)
HA = Hatchery
HC = Hatch
HV = Hovering
I = Icing On The Lens
IB = Incubate
IA = Iowa
IF = Infrared
J = Juvies
JK = Jerky
K = Kleenex
KU = Kudos
L = Leaves
LT = Light
LV = Love
LE = Lens
M = Mom, Mommy
M1 = Mod
M2 = Mod II
M3 = Mod III
MB = Mombrella
MK = Muskrat
MT = Mantle
N = Nest
NIC = Nictitating
NS = Nestorations
O = Owl
P = Parent(s)
PA = Panning
PCH = Porch
PCP = Porch Peeps
PE = Pellet
Pfffft = Poop shoot sound
PX = Pixels
PR = Preen
PS = Poop Shoot
PT = Poptent
PTZ = Pan, Tilt, Zoom
Q = Quiz
R = Rabbit
RF = Raptorfan81
RRP = Raptor Resource Project
S = Stream
SA = Separation anxiety
SN = Snow
T = Tree
TA = Talon
TF = They're Fine
U = Unconditional Parent Love
UST = UStream
UV = Ultraviolet light
V = Victory Of The Fledge
VB = Victory Branch
VE = Venison
W = Wilson
WGZ = Wingersizing
WI = Wind
X = Xtra Knowledge
XO = Kisses & Hugs
Y = Branch
Z = Zoom
ZS = Zzzzzzzzzz's

Special Additions:

eeeeeeeeeeeeeeeee = E1
eeeee eeeee eeeee x infinity = E2
eeeee eeeee eeeee (3x) = E3 (and with a grunt, eating)

Happy watching!

Thursday, March 15, 2012

Peregrine Falcon FAQ

While we wait for eggs to hatch in Decorah, Valmont, and Fort St. Vrain, I thought I would talk a little bit about Peregrine falcons. Prior to the Decorah Bald eagle cam, Peregrine falcon recovery was what we were known for, to the extent we were known at all.

In Flight
The Peregrine is the fastest animal in the world, diving or stooping at speeds that can reach over 200 miles per hour. Almost everything about it is built for speed, from the baffles in its nose  to the jagged edges of its slim, stiff feathers and long, pointed wings.

The falcon catches other birds in flight by diving on them from above.  As she begins her stoop, she rolls, cups her wings around her body, and tucks in her feet. This change in shape streamlines her profile, yielding an aerodynamic raindrop that can cut through the air at high speeds.
Photo used with permission of Karen Carroll,
As she plummets her nictitating membrane, a transparent 'third eyelid', protects her eyes from dust and debris in the air and a secretory gland helps keep her corneas from drying up. A special cone or baffle in her nose regulates the amount of air entering her nasal cavity, allowing her to breathe and protecting her from damage. A curved flight path keeps her prey in view and reduces her aerodynamic drag. Before she strikes her prey, she'll experience G-Forces estimated at between 25-27 Gs.

The Peregrine meets her prey feet-first. She slows first, unfurling her wings and tail, and dropping her feet. After striking and stunning or killing it outright, she'll loop around in mid-air to retrieve it and take it to a safe place for plucking and eating.  
Falcon Belinda at Xcel Energy's Allen S. King plant aims at a reporter.
Lifestyles of the Fast and Furious
Falcons are roughly crow-sized. Females are about a third larger than males, although they both have bluish to slate grey backs,  barred or streaked white to rusty underparts, and a black hood. Adults have black beaks and yellow feet, although their babies may initially have bluish feet.  This is natural and not a cause for alarm.

Both males and females are highly territorial. Like eagles, Peregrine falcons are relatively monogamous (polygamy has been documented, but isn't common) and may or may not migrate. Unlike eagles, they are relatively solitary birds.

Traditionally, Peregrine falcons nest on cliffs, laying their eggs directly on a scrape they created in a gravel or sandy substrate.  In the midwest, Peregrine falcons generally:
  • Lay eggs in late March or early April
  • Hatch in late April to early May, or 33 days after the first egg is laid.
  • Begin flying in mid-June or later, or about 40 days after hatch.
Peregrines make excellent, attentive parents. The babies cannot thermoregulate (control their temperature) until they are about 10 days old, so Mom spends a great deal of time huddling over them while Dad feeds everyone. As the babies age, both parents spend time hunting. The eyrie is small and the babies, which have among the fastest growth rates in the animal kingdom, are large and hungry. They eat, sleep, poop, and go from white fuzzballs to sleek brown juveniles in about five weeks.

Once they begin flying, the young peregrines spend a lot of learning how to fly and hunt: something that looks a lot like play to most human observers. Their parents will continue to provide some food for their newly fledged young who are not yet self-sufficient.  Come fall, the adults may or may not migrate, but their children will disperse. In our experience, the young falcons tend to leave in September. Once they are gone, they are gone. If they do come back to the nest, their parents will defend it from them. 

What to expect when falcons are expecting
The new Great Spirit Bluff nest cam wonderfully documented falcon courtship. The falcons engaged in  ledge displays on the roof of the nest box, bowing and calling loudly.

As courtship progressed he made a scrape, digging into the gravel with his breast and pushing with his legs to create a depression (males and females will do this - our video shows the male).

Finally, both falcons bowed and e-chupped over the scrape.

The male also courts the female with food. Our video shows him bringing it to the nest box, but falcons also transfer prey midair. There seems to be a little bit of food fight here as well, but think some courtship was going on.

She will probably lay three to four reddish speckled eggs sometime in March. Peregrine falcons do not begin full incubation until after egg number three is laid, so it is normal for her to spend time - even quite a bit of time, depending on how warm it is - away from eggs number one and two. Her eggs should begin hatching 33 days after the third egg is laid.

Mae's eggs, Xcel Energy Allen S. King Plant.
Some egg color variation is normal.
During incubation, she will experience hormonal changes that help keep her incubating. She may appear sleepy or lethargic, and will spend a lot of time picking at gravel and sitting more or less quietly on her eggs. She does most of the incubation, although the male will spell her briefly. The male is smaller and may have a harder time covering all of the eggs, depending how many are laid. We can also expect to see egg rolling (Brent, at the Allen S. King plant, is well-known for this) and some shimmying. This is not a particularly active time for the falcons: I've heard Bob refer to incubation as the 'egg doldrums'.

My reference list:

Saturday, March 10, 2012


We are getting a lot of questions about eggs and hatching.  It takes 35-37 days for Bald eagle eggs to hatch, 24-28 days for Canada goose eggs to hatch, and about 28 days for great horned owl eggs to hatch. Despite the differences in incubation times, very similar things happen in the eggs of all three species. 

What happens within the egg shortly before hatching starts?

The rapidly developing embryo...
  • Grows large enough to take up nearly all the space.
  • Positions its body so that its head is at the large end of the egg next to the air space.
  • Begins to breathe with its lungs. Ever crack an egg and see the white membrane inside? Before the chick pokes its beak through this membrane into the air space, a special tissue called the CAM supplies oxygen to the developing embryo. Gases, including oxygen, leave and enter the egg by diffusing through the pores in its shell, across the outer and inner shell membranes, and into the blood in the capillaries of the CAM. From there, the blood circulates through the embryo and provides it with oxygen - no lungs required until the membrane is broken. 
  • Consumes most of the remaining albumen and yolk. When I was young, I thought that birds formed from the yolk. Not so! The yolk provides food and energy for the embryo.
The chart below outlines major developmental points in the lifecycle of a developing chicken embryo. At 20 days, the chicken is almost large enough to break the membrane and begin hatching. The timing would be a little different in the case of Bald eagles, Canada geese, and Great Horned owls, but the stages of development are the same.
Successive changes in the position of the chick embryo and its embryonic membranes. (From A. L. Romanoff, Cornell Rural School Leaflet, September, 1939.) (Fig. 9). Website:
So how do birds hatch?
The embryo has breached the membrane, is breathing air with its lungs, and is head up, with its head positioned at the large end of the shell.
  • Our embryo  uses its egg tooth, a small temporary structure on the op of its beak, to cut through the shell from inside. The eggshell is thinner and weaker than when it was laid, since the growing embryo absorbed calcium from the shell for its bones. The embryo rubs its egg tooth against the shell, which cuts a small hole.
  • As it rubs it rotates its body, slowly cutting a ring around the shell.
  • When the cut is complete, the hatchling bird pushes its body against the shell, forcing it apart.  It works itself free of the shell membranes and halves. Viola - a baby bird!
Here is a time-lapse video of a chicken hatching. The hatchling pips, or makes a hole in the shell, and begins rotating.

Altricial versus precocial
Our hatchlings face very different challenges. Canada geese are precocial - that is, they are relatively mature and mobile from the moment of birth. Eagles and owls are altricial, which means the young are helpless and require parental care. Bald eagle and Great Horned owl parents bring food into the nest for their young, often caching or storing prey for later consumption. This means that eaglets and owlets don't need to leave the nest or procure food until they fledge. The young goslings leave the nest within 24 hours of hatching and do not return to it. While their parents continue to provide protection and care, the goslings feed themselves.

The precocial goslings are also able to thermoregulate right away, unlike the eaglets and owlets. altricial birds require their parents (or a parent) to apply warmth until their down feathers are developed enough to insulate them. The eagle parents and mother owl will spend a great deal of time huddling over their young after they have hatched.


The following resources helped me write and understand this:

Thursday, March 08, 2012

Things are getting busy! Here is a recap of all the action going on at our various nests. Remember, the estimates are estimates only - hatch could begin a little sooner or a little later at any location.

Valmont Great Horned Owls
We anticipated hatch would start on  03/10/12, but regular cam watchers think it may come a little sooner. The Valmont Owl fans are very dedicated and worth listening to, so you may want to check this one out sooner rather than later. Cam link: and click the Valmont Owls link in the list on the left.

EagleCrest Canada Geese
This site has been full of surprises. The hawks have made a nest elsewhere, leaving an open nest tray for...geese? The Canada geese nesting here have laid five or six eggs despite an owl scare. We estimated hatch starting on 03/21/12. To watch EagleCrest's Wild Kingdom, follow this link:

Fort St. Vrain Bald Eagles
The Colorado Bald eagles laid eggs a little earlier than the Decorah pair, but I don't know what I was thinking when I estimated the 24th. I am estimating March 21 here. Remember, this is an estimation only. Cam link: and click the Xcel Fort St. Vrain Eaglecam link in the list on the left.

Decorah Bald Eagles
We are anticipating hatch will start somewhere between March 23 and March 25. Cam link:

Great Spirit Bluff FalconsThe Great Spirit Bluff falcons have been seen copulating and making a scrape, so we anticipate the female will be laying eggs soon. We are trying very hard to get band numbers here - we believe the male is P/(something) but we aren't quite sure about the bottom character yet.

Other Cams and Nests
  • Missouri Turkey Vultures: Waiting for them to come back
  • Riverview Tower Peregrines: Waiting for them to come back
  • Dairyland Power Alma and Genoa: Falcons are back in both locations
  • Red Wing Grain: Falcons are back. A fight between three of them was witnessed by plant staff on March 7th.
  • Hibbard Power plant: falcons are on the grounds. We are considering cleaning out the nest box here ourselves.
  • Agri-Bunge, McGregor, IA: Falcons Bonnie and Clyde are back.
We'll keep you all posted as nests begin hatching. Since I don't like to leave without photos or a video, here is a video by Mick from Great Spirit Bluff this morning. This is the male falcon (the proper word is tiercel). The male is making a scrape in preperation for nesting.

Monday, March 05, 2012

How big is the Decorah Bald eagle nest?

Our moderators are often asked about the size and weight of the nest. The short (and very rough) answer? The nest is roughly 5 feet high by 6 feet wide at the bowl, and weighs about 1367 pounds.
This should give you about the right idea of its size, if not its shape.

So how do you know that?
We haven't measured or weighed the nest, but I can do some rough back-of-the envelope calculations that should come close. We are going to pretend that the nest is a neat cone shape, if only because it is closer to cone-shaped than to anything else. This photograph of Bob lying down in the nest was taken two or three years ago.

Bob is around six feet tall and the nest is a little bigger now than it was then, so I am going to go ahead and estimate it at 6.5 feet in diameter, which gives it a base radius of 3.25. The nest was roughly 4.5 feet high when I was up there in October, but the nest is irregularly shaped and the eagles have been working on it, so I am going to go ahead and estimate it at five feet high. Fortunately, this isn't rocket science! Estimations are acceptable.

The formula for calculating the volume of a cone is (1/3) * pi * radius2 * height. So, (.3333) * 3.1415 * 10.5625 * 5 = 55.3 Or you can just go to an online calculator. I checked my answer at

Now that we have our volume, we need to think about what the nest is made out of. It is in a cottonwood tree, in a neighborhood with other cottonwood trees, maples, and oaks. We can therefore assume that some of the branches are cottonwood, some are maple, and some are oak. Cottonwood weighs about 28 pounds per cubic foot, oak weighs about 46 pounds per cubic foot, and maple weighs about 46 pounds per cubic foot. Since I can't tell which is which by looking at them, we'll take an average of the three, which equals 40 pounds per cubic foot. 40 * 55 yields an estimated weight of 2212 pounds, or a little over one ton.

Earlier today, I gave 2212 pounds as the final weight. Wrong! It was pointed out to me that the nest is not a cone of solid wood - the branches are woven together and it has spaces, albeit tightly packed ones. I cast around a bit for a way to determine this unmeasurable space and finally decided to use the fibonacci ratio of 61.8%. This number, which is also referred to as the golden ratio, or the golden mean, turns up quite a bit in natural series, especially ones that involve spirals. Don't believe me? Check this out:

Once I factored in fibonacci, my final estimate becomes 1367 pounds. Still a creepy thing to think about when you are dangling 50 feet above the ground on a rope attached to cottonwood limbs above the nest.

How big are Mom and Dad?
We don't know for sure, since we haven't captured and measured them, but we estimate about 8-9 pounds for Dad and 11-12 pounds for Mom. Their wingspan is most likely between 6.5 and 7 feet.

So how do you know that?
Again, we don't know exactly. Bald eagles vary in size. Bald eagles in Florida are much smaller than those in Alaska, probably because being large helps animals retain heat in cold weather (check out Bergmann's rule: Iowa has cold winters, so our eagles should be on the larger end of the scale. According to wikipedia (
  • The bald eagle's body length varies from 28-40 inches (70-102 centimeters)
  • The bald eagle's wingspan measures between 5.9 and 7.5 feet (1.8 and 2.3 meters)
  • The bald eagle weighs between 5.5 and 15 pounds (2.5 and 7 kilograms)
  • Females average 13 pounds (5.8 kg) and males average 9 pounds (4.1 kg)
Kay Neumann from SOAR (Save Our Avian Resources) has a lot of experience weighing and measuring bald eagles that come into her rehabilitation center. Although these eagles are often sick or injured, and so may be a little lighter than a healthier eagle, she said:

"Males are weighing in the 8 to 9 pound range, and females are in the ten and eleven pound range. I’ve heard the Raptor Center (Amy's note: the Raptor Center at the University of MN) say from 8 to 12 pounds, and that seems about right for our Iowa birds too. The record holder is a 14 pound female, but she may have been a Canadian bird. So there is quite a bit of a range – just like people, eagles come in different sizes.
It is a bit deceiving in that they look as big as a turkey – 20 pound birds. Turkeys are designed to wander around on the ground and look for seeds while eagles are designed to fly and so built quite differently. An eagle has hollow bones and feathers for strong but light construction - just like a plane."

How big are the eggs?
The eagle eggs are oval, white, and roughly the size of a tennis ball. The Center for Conservation Biology at the College of William and Mary has a wonderful post on this:
Bald eagle eggs weigh about 4.2 - 4.5 ounces (120-130 grams) and range from 2.3 to 3.14 inches (6-8 centimeters). They are 1.96 to 2.3 inches (5-6 centimeters) wide. They are hard-shelled. Everyone knows that eggs can't get too cold, but they also can't get too hot. Cam watchers have noticed the eagles seeming to spend a little more time off the eggs this year. This may be in response to the (relatively) warm winter. For more about the eggs, check out this blog:

How big an animal can a bald eagle kill? For instance, can a bald eagle kill a deer? How much weight of prey can a bald eagle carry to the nest?
We don't know the biggest animal that a bald eagle can kill, although I have some prey weight estimates based on animals we have seen them carry up to the nest. Golden and Harpy eagles kill large prey, including deer, but I have not been able to find a reliable report of a bald eagle killing an adult deer. In general, a Bald eagle won't kill you and carry you away if you weigh over about 4 pounds.

The internet gives a lot of interesting answers when about bald eagles and prey weight. I think the Carolina Raptor Center gives the best answer: they can lift half of their weight and carry 1/3 of their weight. Based on these estimates:
  • Mom can lift about 5.75 pounds and carry about 3.8 pounds
  • Dad can lift about 4.25 pounds and carry about 2.8 pounds
These estimates are in line with the prey we have seen brought into the nest, which has included:
  • Fish. The Decorah bald eagles seem to prefer fish to everything else, which means that the majority of their prey is probably around 1 -2 pounds. No muskies, but a lot of trout and sometimes suckers.
  • Muskrats. Wikipedia tells me that adults weigh from 1.5 to 4 pounds
  • Wild rabbits. Weight reports really vary, but estimates tend to start around 3-4 pounds for adults. The young are considerably lighter. 
  • Gray squirrels. Again, estimates vary but in general adults weigh .8 to a little over 1 pound.
  • Various birds. Again, I don't know how much they weigh exactly, but the average would be under a pound.
Having said that, I don't think I will ever forget this capture, taken in 2009. One of the adults (probably Mom) brought in the head of a dead fawn (young deer). A newly born fawn might be just inside the range of an eagle's carrying capacity (3 to 5 pounds), but we think the deer was most likely road kill, especially given how deteriorated its body appears to be.

Click here for a look at the area around the eagles nest.

Resources that helped me write this:

Thursday, March 01, 2012

What is infrared light, and why can't eagles see it?

We are starting to get a lot of questions about the night-time illumination of the nest, so I thought I would write a little bit about visible light, invisible light, and our IR illuminators. What we see - the world of visible light - is just a tiny fraction of all the types of light that exist. Infrared light, gamma rays, X-rays, ultraviolet light, microwaves and radio waves are all types of invisible light. Like visible light, they are different because the length of their waves is different.

The illustration below shows the electromagnetic spectrum in its entirety.  The IR portion hangs just off the red end of the visible spectrum.  It spans the frequency range from 780 nm to 300,000 nm (.78 to 300 um) and has a longer wavelength and lower frequency than visible light (click the image to embiggen it):
Illustration courtesy Wikipedia:

Birds have very different eyes than we do. They have four color cones instead of three, more cones and rods to see color and light with, a higher proportion of cones to rods (at least in diurnal birds), and different peak sensitivities to light. As the graph below illustrates, we have narrower spectral sensitivity than birds and are much less sensitive to certain wavelengths of light. However, like humans, birds do not see above about 700 nanometers. While some birds range into UV, IR light is as invisible to them as it is to us.
Illustration courtesy of "Color Vision in Birds":
So how can we use an IR illuminator to see the birds if we can't see IR light?
Researching and writing about this stuff makes me want to read a trashy romance novel, but I'll put that aside for now and forge ahead. Here is how it works. The IR spectrum starts at about 780 nm. The LED IR illuminators used on our camera emit 'invisible' light at a wavelength of 850 nm:  well above the 700 nm visibility limit we share with birds, but well below the high-energy 'hot' end of the spectrum.  LED illuminators are also smaller and have lower requirements and range than bulb-type illuminators.
The camera and illuminators are located roughly five feet from the eagles. The illuminators shine IR light on the nest. The IR sensor detects the light and focuses it onto a CCD (Charge Coupled Device) imager chip, which has a spectral response of up to roughly  1,000nm. The chip maps IR wavelengths of light down into the visible spectrum via tiny electric charges generated by IR light falling on to an array of tiny sensor cells. Since the photo-sensitive cells don't distinguish between colors, the camera generates a monochrome image. I suspect it is really a LAB color space, but that is far outside the scope of this discussion. If you feel really nerdy, follow this link to learn more about LAB color spaces. There is a lot more to color than RGB, even for us trichromates!

Can the eagles hear or see the PTZ camera?
The cameras use servo motors to drive the camera along a 360 degree path, which minimizes the amount of time and work it takes to arrive at any given destination. These motors are very quiet - the camera was designed for surveillance - and encased in hard plastic. I suspect that the eagles can't hear the servos; certainly, we don't hear the servos and the microphone is much closer to the camera than to the eagles. If the eagles can hear the servos, the sound is not any more alarming to them than the other noises that make up their sonic landscape - traffic on the nearby road, people at the fish hatchery, wind, tree branches, the brook, the horses, and so on.

Although the young eaglets went through a period last year of seeming quite fascinated by the camera - we wondered if they were interested in their reflections - the eagles ignore it generally. Since it rotates around a 360 degree axis, there does not appear to be much movement (think of a spinning top) and the camera is behind a dome, which helps conceal it. If the eagles can detect movement, it isn't bothering them. Again, a lot of things around them move. Since the camera isn't trying to eat or threaten them, it doesn't really concern them.

In short...
Mammals and birds can't see IR light - to the eagles, the nest is dark at night - but our camera can. We use low power IR illumination devices that are roughly five feet from the eagles. They are not hot and do not emit dangerous radiation or noises. A chip inside the camera does the work of converting the IR image into visible light via tiny electric charges. However, because the chip does not detect color, the image is monochrome.

Experimenting with IR light
To see IR light for yourself, take a television remote, which works via IR. Press a button and look at the LED on the end. You won't be able to see anything. Now, take a digital camera or phone camera (I used an Android HTC), point it at the remote to take a photo, and press a button on the TV remote. You should now, through a digital device with a higher spectral sensitivity than either we or the eagles have, be able to see the infrared light. Like our camera, your camera uses a CCD chip that maps IR down into visible light for humans. But neither we nor the eagles can see IR without technological assistance. Again, the nest is dark at night.

What about the cameras?
A lot of people are interested in knowing more about our cameras. Read this blog post for more information:

The following sources helped me understand all this: