Thursday, February 24, 2005

JOHN BLAKEMAN ANSWERS SOME GOOD QUESTIONS

Marie,

Here are my answers, however incomplete, to the wonderful ones from Donna Browne. Donna obviously has some experience and thinks like a good field biologist. Here are her questions.

Donna:
“Does anyone (Blakeman?) know how prevalent Pale Male's genetic coloration is or whether it is gender linked?”

JB:
I've watched and trapped a pile of red-tails in 35 years, and I think I've seen just one or two with light-colored heads. In northern Ohio, I'm certain that the coloration isn't common. But it’s interesting to note that eastern populations or races of the red-tail tend to be lighter-colored, western ones darker. So this may be a local genetic tendency. Someone from the Hawk Mountain, or better, Cape May, New Jersey, hawk migration stations could better answer this.

Donna:
“I find it interesting that the Pale Male progeny of Pale coloration, at least the ones I've heard about, are male.”

JB:
As to the color being sex-associated, I have no real information on that, either. But I'm betting that it’s not sex related. I know of no other sexual dimorphism (differences between the sexes) in red-tails that are color based. It’s all size, as far as I know. Sure would be interesting to find out, though. Let’s look for a blond-feathered female.

Donna:
"Does one gender have more of a tendency to range? Did I not read that a female RT not only takes into account the male himself but also his nest site and territory in making her choice?”

JB:
For this, I personally think there is no doubt that females mate not just with the male himself, but with all the territorial accouterments he brings to her attention, including good perch sites, abundant prey, absence of “significant others” (competing adjacent hawks) and all the other things good mothers consider. No, it’s not just sex (we males do have a hard time figuring that out). As I think I mentioned before, the paired hawks are as much mated to their territories as they are to each other.

Reminder from Marie: Don't forget that when John Blakeman uses the word "mate" he is not referring to the sex act. Scroll down for a discussion of "mate" vs. "copulate"

Donna:
“Does it make sense that once a male has a nice nest site and territory that he would range less far than a female who's looking for a male with a nice nest site. Therefore would more of the female RT's in the park be non-related. OR...As half siblings have been known to procreate successfully in other species, and Pale Male has had four mates...?”

JB:
Wow. I like this thinking. It does make absolute sense that young males should not disperse as far as females. Once a male claims a territory and starts circling in the air (raptorial strutting, as it were) to attract an on-the-look female, he certainly isn't going drift off. He’s going to stay right in the area he claims and do all he can to attract passing females..He’s not going to leave his claimed territory to try to bring in any distant female. He can only attract passing or wandering females. He will stay put.

But the questions for our Central Park birds is a) really where have they spent their first fall and winter, and b) have they then come back to their natal area? Without banding data, it’s impossible to tell. The core issue, again, may revolve around prey availability. If the fledged young learned in the summer that CP just has piles of available food, they will never forget that, and when hungry, may attempt to return, even at the threat of being driven off again by mom and pop.

Where do all the CP fledglings disperse to? Just up the river a bit, or do they drift off to all parts of the northeast or elsewhere? One thing falconers know is that first-year birds have a very strong migratory urge. Those of us flying new-trapped first-year red-tails have to be particularly watchful of weather when hunting our birds in late September and early October. Depending on the personality and training of the particular bird, a falconer may not be advised to fly his hawk on a crystal clear, warm, slightly windy day in late September. A red-tail just loves to spiral up in the thermals or such weather, and in just two or three minutes she can be at 500 or a thousand feet. In most cases, the falconer can lure her back down with a tidbit of fresh meat on the raised fist. But from time to time the hawk just sets her wings and starts to drift southward, never to be seen again. Experienced falconry birds being flown in subsequent years seldom, if ever do this. First year red-tails do have a strong autumnal migratory urge. The CP offspring may spend their winters in Georgia or Florida (like a some humans).

Donna:
"There are so many questions and none can be answered about the Central Park Red-tails until we figure out a way to tell them apart without banding them. They currently trust us; we can't blow that. Wait. They can now gender test birds using a feather. I wonder if that is actual DNA testing or testing for testosterone? "

JB:
Once again, exceptional thinking. I'm not an expert on this, but I do believe if someone were to collect a feather that was surely seen to fall from a known bird’s body, DNA or chromosome characterization may be possible. But the problem is that first-year birds don't drop any feathers until the spring after they fledged. That doesn't do us any good, as they may be anywhere east of the Mississippi then.

Trapping and banding is the only good solution, but this won't be possible (or advisable) in NYC. Be assured that when properly done, it does not disrupt the hawk’s “trust.” What it does do is make the bird almost impossible to ever trap again. Hawks remember remarkable details of how they capture food, and trapping always entices their approach with food. When trapped, they will never in a decade ever forget what brought them to the trap. Only when a previously trapped bird is starving will it ever approach a moused trap again. And again, raptor traps use no steel or springs, and cause no harm, pain, or injury to the hawk whatsoever. But trapping in Central Park is utterly out of the question.

There is only one other ID method that could be considered. Lincoln Karim’s remarkable photos of the red-tailed hawks of Central Park are, without doubt, the finest photographs of this species in the wild. I am continually awed. Here’s a photographic ID consideration, if possible.

We can't much tell birds by their feathers, except as to general patterns and colors. Between the immature and adult feathers, between the first and second years, there is far too much variation to connect a second year bird with a previously known bird on the nest.. But there is one structural feature that doesn't vary from molt to molt. It’s the bird’s “scale print,” the individually unique pattern of the scales of the legs. An extreme close up of these when a hawk is perched can allow identification any time later in the bird’s life – if another telescopic macro shot of the same leg could be taken. It’s a daunting task, but one that should be considered. Let’s think how this might be facilitated.

Mary Lewis's Question:
And now for a final fine question that was forwarded to me. Mary Lewis learned that Canada geese, during incubation, warm up their naked feet to help keep the eggs warm. She wondered if there was any evidence for this in our red-tails. In late March it’s pretty cold up way up there in the wind.

But no, I don't think heat transfer out of the legs or feet of the hawk has any significant warming effects. Here’s why. First, unlike a goose, a hawk’s foot doesn't have much surface area. And when they begin to sit, they fold up their feet into closed fists. Sitting hawks, especially our giant red-tails, are particularly attentive to this. They are very careful to fold the talons back under the toes, so as not to inadvertently poke a delicate egg while sitting or standing on the nest. If anyone gets to watch a sitting exchange, when one hawk rises to allow the mate to take over incubation, watch the deliberate delicacy with which both birds move their legs and feet. They will place their legs in the nest next to the eggs, but not necessarily in direct contact with them. It’s the transferred warmth of the naked abdominal brood patch that does the job.

Sincerely,

John A. Blakeman