Chris Lyons reports and speculates on orange chests

The three Fordham nestlings --two orange and one white


White-chested Fordham nestling
Photos by Chris Lyons


Chris Lyons reports on the Fordham University redtail family, whose nest is reminiscent of Pale Male's on Fifth Avenue , from the architectural ornamentation in the background to the anti-pigeon spikes at its base. He also casts new light on the mystery of the orange-chested nestlings.

*********************************************************

It's been an exciting week at the Fordham nest. The first fledge of the year took place on Thursday evening (6/8), around 5:35pm, and I was actually there to see it. I didn't expect fledging to happen quite that soon, and the reason I hung around after work was to try and photograph all three chicks together on the nest, which I just barely managed to do before the coming out party.

And as you'll see from the photograph I took of the trio, plus an earlier photograph of one of the chicks in particular, two of them have orangey chests, and one decidedly does NOT. I had noticed this difference a week or so ago, but I wasn't sure if the pale-chested eyass was just a late bloomer, so to speak. In some light, you can see a little color here and there, but the difference is obvious in any light, and if he doesn't have an orangey chest by now, I doubt he ever will. And his sister (the largest, and first to fledge) has something of a pale spot in the midst of her otherwise orangey chest. The third eyass just has a regular orangey chest of the type that has become familiar to all NYC Red-Tail fans. I never anticipated I'd ever have occasion to type the words 'orangey chest' so many times in one paragraph, but there you have it.

So what to make of this? Hawkeye and Rose had two orangey-chested chicks last year. The year before that, I firmly believe, they built a nest on a nearby fire escape on Creston Avenue, which produced two chicks, both of which were removed from the nest when they were still too small and fluffy to have developed orangey chests.

They were taken to an upstate raptor rehabilitation facility, where they were successfully reared and released by Paul Kupchok. Who, when I spoke to him, was fairly certain they both developed that familiar chest pigmentation. But who stated quite definitely that both orangey-chested and pale-chested eyasses were commonly brought to him from all parts of New York State. We didn't get into the matter of whether you could have both in the same clutch. But self-evidently, you can.

We all know that the genetic lottery is a funny thing. You only have to look at a litter of mixed-breed puppies to know that, and even pampered purebreds produce their share of oddities, which is how we created so many breeds of dog to begin with--by breeding animals with rare but desired traits with others having the same traits, until the type breeds true. With humans, a red-haired child can be born to a family of blondes or brunettes, a living reminder of some forgotten forebear, perhaps from an Irish bog, or a Polish shtetl.

Red-Tails move around. The young fledged from one area are forced to leave their parents' territory, and while they may settle nearby, they may also end up very far away. Red-Tails that don't have territories as bounteous as Pale Male and Lola's may migrate many hundreds or thousands of miles to find a good wintering spot. We see many more Red-Tails in NYC in the wintertime, because birds from up north have come to feast on our teeming population of rodents (and increasingly, pigeons), in an effort to survive until the spring, at which time birds with established territories may head back north, but those without may sometimes hang around and mingle. Local talent meets out-of-towners, and birds from different areas end up producing young together, rolling the genetic dice again. As John Blakeman has pointed out, this is the key to longterm genetic fitness and adaptability for this species, and many others. The greater the genetic variety, the better.

So the pale-chested eyass gene (pity there's no Red-Tail Genome project) is commonly found among Red-Tails in the areas surrounding NYC, but for whatever reason, it's been either rare or recessive in the urban-nesting birds we've been observing--and even looking at online photos of eyasses from other parts of the country, Boston, Hartford, and even California, one keeps seeing those orangey chests--even though there seems to be no mention of this chest coloration in the literature compiled by scientists who have studied this species. The one thing that all these nests seem to have in common is that they aren't out in the wilderness--they're all close to human habitations, and easily observed by nature enthusiasts. So they may give a skewed idea of how common this trait really is. Or they may not.

Maybe the orangey-chested eyass gene is the dominant gene--that's certainly the case with human pigmentation. Where a Red-Tail carrying the pale-chested gene mates with a Red-Tail that has the orangey-chested gene, the offspring usually (but not always) develop the orangey chests. But of course, the chicks normally don't keep their orangey chests--in these parts at least, they start turning pale again, in the months following fledging. So what on earth are these orangey chests FOR? Why did eyasses start developing them in the first place?

Well, I might as well throw a theory out there to get shot down--just to get the ball rolling.

It's well known that birds are highly sensitive to color--all birds have excellent color vision, whereas very few mammals do. They can probably see color better than we can, and perhaps color 'wavelengths' that we can't detect at all. Nestlings of many bird species display brightly colored gapes in their early stages of development, that scientists believe may help stimulate their parents to feed them (the stimulus is so strong that a Robin was once photographed feeding goldfish in a pond, whose orange gaping mouths at the surface triggered his powerful feeding impulse). Even the dark-hued Raven, when young, has bright orange coloration around the beak--I've seen Ravens chicks being fed on a nest high up on the Palisades, near Nyack--and the gape color is visible from a great distance.

Now, it makes no sense that this chest coloration exists to stimulate Red-Tail parents to feed their nestlings, because the nestlings don't HAVE this color for most of the time they are on the nest. Hints of it may be seen in otherwise pale fluffy chicks, but it reaches its peak not long before fledging, and fades not long after. So in fact, it's at its peak during the time when the eyasses are still highly dependent on their parents for food, but no longer in a single convenient location. They may band together at times, but at other times, they'll be scattered, perched on trees or human structures, vying for the increasingly divided attention of their parents, competing for the food they need to finish maturing. By the time the color fades, the young have probably started hunting for themselves, and the pigmentation is just a waste of resources now needed for the young bird to develop its first adult plumage, and (of course) the famous brick red tail.

So just for the hell of it, I'm going to speculate that the orangey chests found on so many Red-Tail eyasses are a relatively new adaptation (which would explain why they have not been more remarked upon by past observers), and give those chicks having them a slight edge over pale-chested siblings in terms of attracting their parents to come feed them. I don't think it makes them more visible, necessarily, but it may make them more attractive, in a sense--the color may stimulate their parents to come to them just a BIT more often. If it gives them any edge at all, it's probably a tiny one at best. But in the genetic sweepstakes, a tiny edge can be significant over the long run. The trait is probably more common in some areas than others, but may be spreading through the normal process of young hawks striking out on their own across great distances, to find food, a mate, and a territory of their own. It's conceivable that someday, pale-chested eyasses may become as rare across much or all of the enormous range of this species as they are in New York City.

But as the little guy flapping his wings at us in the photo seems to be signaling, the pale-chests aren't finished yet. Maybe if we look harder, we'll find more of them. And maybe we can find a better theory too, but I just thought I'd take a shot at it. Anyone want to take a shot at my theory?