Friday, June 02, 2006

Orange-chested nestlings: Is it the diet? Chris Lyons investigates

Orange-chested chicks at Cathedral of St. John the Divine
Photo by Bruce Yolton

Chris Lyons, a careful observer of the Fordham redtail family [Hawkeye and Rose and three kids], has been looking into the orange chest mystery. Specifically, he's been researching the notion, promulgated by John Blakeman in a recent posting, that the orange chest is a result of diet, not genetics. Since two chicks of a previous Bronx nesting [on a fire escape!] ended up at a wildlife rehabilitation Center near Brewster, New York, Chris contacted Paul Kupchok, the director of that center, to ask about the diet of those chicks. Here are Chris's findings:

I explained to Mr. Kupchok about the two chicks from
the 2004 fire escape nest in The Bronx, that I believe to be Hawkeye and Rose's progeny, and he remembered them well. Both were successfully reared to young adulthood, and released in August of that year, not far from the center. As he recalled, both of them did develop the orangey chest color--he wasn't 100% certain, but he said there would be photographs of them at different stages of growth, if it had to be confirmed. He was pretty sure they did develop that color.

Mr. Kupchok said he never feeds pigeons to the raptors in his care. He was quite emphatic on this point. They mainly get field mice (live ones, in the latter stages, when they're learning to hunt). He said that aside from the fact that he has special feelings for birds that make it impossible for him to sacrifice the lives of pigeons to feed hawks, he also thinks it's very dangerous to most raptors to feed them Rock Pigeons, because of the diseases this species can carry. He says maybe urban hawks have developed resistance, but a pigeon diet could be deadly for those that haven't. For this reason, he probably wouldn't be feeding them city rats either (and they'd be kind of hard to obtain where he is, anyway). I'm not quite clear on whether the diet would be 100% field mice, but that was the impression I got.

Mr. Kupchok has been rearing young Red-Tails and rehabilitating injured ones for about 20 years now. He says that during that time, he has seen many Red-Tail eyasses, from all parts of New York State, some from well north of where he is, and that many developed the orangey chest color, and many others did not. It seems to be a very common genetic trait, but not a universal one. He was sure he'd seen eyasses from before Pale Male's time that had that coloration--and in any event, very few of the birds he raised were from New York City (probably just the two from The Bronx, but I forgot to ask). He certainly was open to the possibility that it was a common trait among New York City Red-Tail chicks because of Pale Male's genes, but of course it could just as easily be possibility that Red-Tails with the tendency to produce orangey-chested eyasses are more likely to exhibit this type of nesting behavior, but damned if I can see how you'd go about proving that.

All this new information by no means disproves the theory that Pale Male's genes are widespread among the local Red-Tail population (I think it would be odd if this were not the case), but the orangey chests basically don't prove much of anything. It just so happens that the Red-Tail eyasses that John Blakeman and Len Soucy have seen did not have this coloration. It's not an uncommon trait at all.

I personally believe that the colonization of New York City by Red-Tails was a gradual process, that involved many different birds, coming from New Jersey, Westchester, and Long Island, and probably some from further afield--but I still believe Pale Male is an important contributor to the local gene pool. Possibly not a predominant one, though. And there is no reason at all to think his genes are predominant outside the immediate area. When we see Red-Tail eyasses with orangey chests around Connecticut courthouses, or Boston college campuses, there is no reason to assume they have anything to do with Pale Male. It's possible, but not much more likely than that he's related to the orangey chested eyasses that Anthony Galvan III photographed in California last year.

We just don't know enough about this species, and its incredibly wide distribution and genetic diversity, combined with its great variability in plumage, make it dangerous to overgeneralize on the basis of physical appearance. There's still disagreement on the subject of whether the Harlan's Hawk is a separate species closely related to Red-Tails, or simply a Red-Tail subspecies with a distinctive appearance (the former view is currently prevalent among ornithologists). Even when careful DNA testing is done, there are questions that still resist definitive answers.

And the field mice diet the transplanted Bronx chicks got from very early in life tends to rule out the theory that the coloration comes from eating city birds and/or rats. As well as the fact that Mr. Kupchok has seen so many eyasses with this chest coloration from all over New York State, for the better part of 20 years.

So basically, we know nothing.