A while back reader Gregory sent an nice set of pictures of the process of banding and testing the chicks and adults of a Coopers Hawk (Accipiter cooperii) who had nested in his neighborhood. Here is his story and the pictures of the banding (and other bird-related items):
In 2007 and 2008 we had a Coopers Hawk nest in front of our home in Milwaukee. Then, in 2009, they moved their nest a few blocks away. During these years the nest was visited by an ornithologist (and one time, two of them) who climbed up the tree and brought the chicks down for banding and blood draws. One year they used a net and a rescued owl to capture the parents for blood testing, too. (The owl was blind in one eye and as a result is available as an assistant in the capture process… Coopers chicks are prey to owls and the parents freak out, try to chase the one-eyed fellow away, and end up in the net.) [JAC: That’s amazeballs!]
Anyway, I took lots of pictures and there are some I’m sending along… hoping they get through the email system. I was able to hold one of the parents during the process and was amazed at how much heat they radiate. It was an adventure having them on the block. I miss them, although I don’t miss the small bird body parts that littered the sidewalk under their dining trees. 😉
JAC: The young of many predatory birds (including, you may have noticed, the Great Horned Owl) are covered with white down. I wonder why the color? It wouldn’t seem to be cryptic, as white chicks stick out like a sore thumb. It might just be a developmental constraint, but I doubt it (down doesn’t have to be white!). Perhaps readers have suggestions.
Look at those talons. They’re huge!
The bait!:
I decided to send three more… One shows the male (I think) just about to have his blood drawn. The other two I include although they are a bit unhappy. In the second year of the nest in front of our home, the chicks died a week or so after they were banded. We believe it was the result of raccoons, who apparently climbed the tree. I took a photo of one chick, dead, on the sidewalk below the nest. Then the following year, in the nest a couple blocks away, some of the eggs had died although two chicks were doing fine. I took a photo of one of the dead eggs after the biologist at the scene tossed it out on the boulevard. Sad things happen in the wild.
White down on chicks may be an assist in thermoregulation? Even though birds are homeothermic, chicks are restricted to the nest and so are perhaps subject to a great deal more solar radiation than adults, which can move into a shade mosaic to help regulate body temperature. The juveniles and subadults probably experience more freedom of movement as they mature and their adult plumage develops.
FWIW… Coopers nests, at least in my neighborhood, are all in very shaded trees.
Poor Polyphemus-like owl exploited for his disability. 😉
I would love to hold the cute raptors – not that male one though; he looks really pissed!
Old Mr. One-Eye seemed completely oblivious to the entire capture process. Maybe he was just jaded from having done it so many times. Or perhaps lacking stereo vision made him unaware of the angry parents.
“exploited for his disability”
Bird banders are highly motivated to take good care of the bait owl. After being in captivity for a bit, a bird like that calms way, way down. That owl thinks nothing of captivity or the proceedings of trapping and all.
“I would love to hold the cute raptors”
Look again at the photos of the fluffy ones having bands applied. Do you see how the handlers have the legs all straight? That grip precludes getting footed (grabbed by a talon) by the sweet young thing.
I’ve been footed. You don’t want one. The accipiters are said to go for the face, though I haven’t had the priviledge.
Well I was joking about Polyphemus and I know they can claw the crisp out of you, but GBJames got to hold one with their help so I could too.
If they get a foot in you, the aggressive behavior is astounding. They want to sink those talons all the way in, right up to the knuckle. I haven’t gotten one of those, but I saw one once…oh, ouch!
Damn straight you could do it. But to get good at it takes a while.
I was able to do that under the careful guidance and assistance of the ornithologist who handed the bird to me very carefully. I wouldn’t have wanted to attempt it on my own. The bird didn’t struggle. What I remember most vividly, as I mentioned earlier, is how warm the bird was.
Here is a guess from an grossly unqualified amateur evolutionary biologist. In later life a bird would maximum their fitness by having a coloration that would result in their not being noticed by prey and preditors whereas the chick in the nest would maximize their fitness by have a coloration that would make them the most noticed in the nest and hopefully be the best fed in the nest. The nice thing about down is that it is warm and bright and once you are old enough you will have grown out nice drab feathers that will allow you to blend into the environment.
I’d never thought about fluffy down as an attractor before, that’s interesting. I know nature rewards the biggest, reddest gaping mouths for sure – maybe the two traits go hand-in-hand since they both signify robustness.
Although it seems the most vulnerable time by far for all birds is prior to flight, while chicks or in egg form.
White radiates out less heat from a body than any other color. Are nestlings in warm climates ever white?
Yes.
I watched either a Cooper’s or sharp-shinned hawk that was perched in the walnut tree out back for quite some time yesterday. Moments ago I went out on the patio and heard some fluttering and saw he was back and perched on a fence. Just before 9:30 am PST I heard some commotion and looked out and saw he had captured something. By the time I quietly opened the patio door all that was recognizable were a few remaining feathers that he was sifting through for additional goodies.
Maybe, with parents like that, it doesn’t matter what color the chicks are.
Why white down? I can’t come up with good explanation. I don’t think it thermal regulation because they nest in tree’s (baby bald eagles are also white but they tend to nest in direct sunlight). Although I like MAUCH’s, “Mom likes me best” explanation, I can’t make that work if all the chicks are white. So, my question would be, do we ever see chicks of the species that are not white? Maybe the color white was selected a very long time ago for ancestors that nested like eagles and the mutation(s) that would make them darker have not yet appeared. Or maybe, white wasn’t selected for at all. Maybe there is some other quality of the down that was selected for and white just happens to be another characteristic of the same set of genes.
Here’s an idle speculation on the coloration issue: raptors may be less concerned with predation than smaller birds for various reasons – they’re larger and the parents are better equipped to fight off predators; they tend to nest high and probably largely out of reach or notice of many predators and opportunists. Cryptic coloration would be of limited use. What if their white down is just an absence of coloration – no particular reason at this point to have any for display or disguise, so they just don’t produce melanin?
Perhaps there’s an energy cost associated with producing pigmentation.
I had the same thought. Why expend extra energy (melanin) on down feathers when a full set of feathers needs to be grown.
Melanin also makes feathers stronger; perhaps it interferes with properties of insulation. Most (all?) birds have white downy feathers beneath their contour feathers for insulation.
That makes sense to me. But, it still doesn’t clear up “why white?” Why not yellow (cockatiels,chickens) or more specifically for this species, why not green (since they nest in trees)? The only thing I could I think of is that white has such a low energy cost that it would offset the predation cost. I don’t know how an ornithologist would test that, but I’d fascinated to find out.
Using an owl to capture Coopers Hawks? Now that is a new one on me.
I wonder what they look for in the blood.
They were studying the spread of a blood parasite that is moving north from Texas, if I remember correctly.
Works like a charm, too. Set the owl on a stump and stretch a mist net above them. Play a recording of a Cooper’s vocalisation to get the hawk’s attention and bingo, a very unhappy hawk being banded. It’s so compelling for the hawk you can come back next year and do it all over again.
http://www.hawkwatch.org/our-work/research/blood-sampling
I’ve also done fecals to detect the Borrelia bergdorfori (lymes disease) spirochete in rodentivores. Likely they are also testing for West Nile virus antibodies.
Aha…thanks for the additional info GBJames and Kamakanui.
The reds and yellows are a different pigment type called carotenoids, which pigments are not manufactured by animals, only plants. Chickens accumulate lots of it in their diet, raptors, not so much. A bald eagle’s yellow beak is pigmented by carotenoids from eaten prey.
Aha! Chickens and cockatiels are (for the most part) vegetarians unlike the raptors. Now your previous comment makes even more sense. Thanks!
OK, now what about ducklings? Do they get their yellow color from the fish that they eat (assuming if you go down the food chain far enough you get to plants)? Kamakanui, if the answer is too complex, I’m OK with that. The biggest thing I love about science is one question leads to another. But, when it comes to biology, sometimes I don’t enough to know what I don’t know.
There are just a few domestic species of duck that have yellow chicks. Most ducklings are cryptically colored in (melanin) grey, brown and black.
There aren’t that many ducks that eat fish as a primary diet item. Most of them are eating vegetation and invertebrates, the latter often high in carotinoids. But carotinoids can be aquired eating fish, as the bald eagle demonstrates.
Are you aware that another way for birds to express color is through refractive feather structure? A mallard drake’s iridescent green head is a combination of carotinoid yellow and refractive blue. If a bird’s color changes depending on the angle you are seeing it, that’s refractive; think indigo bunting.
Thanks Kamakanui! You went above and beyond.
“Are you aware that another way for birds to express color is through refractive feather structure?” I had no idea. Can you point me at some good books? Not necessarily just about birds, but about colors in animals in general.
Refractive blue: the physical structure of the feather reflects blue spectrum colors and absorbs other colors quite well.
Colors in animals, here’s a start:
http://www.pnas.org/content/106/Supplement_1/10001.full.pdf
Let me recommend some nice bird books.
Bird Feathers: http://www.amazon.com/Bird-Feathers-Guide-American-Species/dp/0811736180/ref=sr_1_1?s=books&ie=UTF8&qid=1424053268&sr=1-1&keywords=bird+feathers
The Crossley ID Guides:http://www.crossleybooks.com/