Monday, April 11, 2005

12/13/04 -- Blakeman's Concerns about Various proposals


Subject: Re: Rooftop nestbox won't work (Ohio redtail biologist)

Date: 12/13/2004

Marie,

A NY Times reporter, "Jenny," just called and aske me a fine list of important questions, mostly related to the nesting information I sent you yesterday.

I think the questions and answers were helpful in getting things back to where we want them, without any unforeseen untoward consequences (such as a nest box).

Let me know how I can help in any other way.

Sincerely,

John A. Blakeman


Subject: Re: Rooftop nestbox won't work (Ohio redtail biologist)

Date: 12/12/2004

Marie,

Here are some considered, experience-based answers.

I'd have no concern about the construction of some structural device to retain either nest sticks, or even dropped meal leavings (although that would quickly become clogged with the tremendous quantity of leavings they produce). The birds are attached to the ledge, no matter what's on it, so long as it stays open (no box).

The reinstallation of the pigeon-repelling pins would be ideal, as sticks would once again be lodged between them. Any similar arrangement would work.

And here's an important point -- one that I wouldn't want opponents to misrepresent. The destruction of the nest appears to be catastrophic, but if the stick-holding metal pins can be reinstalled, all of this activity, as destructive as it might appear, will actually have increased the pair bond. The forced rebuilding of the nest is actually a good thing, something we see in wild pairs.

You recall that I stated that Eastern redtails seldom use a wild rural nest in consecutive years. They build a nest in a tree, raise a broad there, and then in the next year they select an alternate site a quarter mile away. The first nest was in perfect shape and needed only a nest-bowl refurbishing with the mere addition of a layer of some small fine layer stuff at the bottom. But instead of doing a slight rearrangement (equivalent to merely getting a new set of sheets), the birds simply abandon the nest and go down the road a ways and build an entirely new nest.

This requires a great deal of effort, pulling off sticks, carrying them to the new tree crotch, and then trying to get them to balance until a sufficient, self-linking pile has been placed there. But the psychological effects of this inordinate new nest-building effort actually strengthens the birds' pair bonding (their mutual "love," as it were) and this also apparently really gets the breeding hormones flowing. In short, do not be concerned that the nest destruction, by itself, has been terribly disruptive. If the nest can be rebuilt, the birds will be quite OK. Nest rebuilding is normal and psychologically helpful. But the inability to complete the nest, making it ready for fine nest lining and sitting-in, as some many have seen the birds do, would be extremely disruptive.

If that happens, however; if the nest cannot be rebuilt, the pair may go a year without copulating or nesting. They may just float around Central Park, or may even drift over to Jersey or somewhere, and then return in the late winter of '05 and start things again. It is not uncommon for an old reliable redtail pair to take a year off. This is usually precipitated by the loss of a nest, when the tree blows down, for example. But the pair usually comes back the next year and goes at it again.

So, if the nest isn't rebuilt this year, not all is lost. The pair is likely to return, to search once again for a good nesting ledge in the area.

And while I'm thinking of it, take this thought into consideration. Pale Male is what, 10 or 11 years old? From nesting redtail population studies in Ohio I've been involved in it's estimated that the average longevity of nesting wild adults is about 7-10 years. But we have pairs that are known to have nested consecutively for nearly 25 years. We think now, in retrospect, that these long-lived pairs actually involved any number of birds. A member of the pair would die or drift off and bond with some other bird any number of miles away. The nest was always used, but the members of the attending pair probably varied. Of course, this is exactly what has happened with Pale Male. We know that it's almost always the male that selects a nest site and begins nest construction in an effort to lure in a female mate. Pale Male has been typical in this process.

Regrettably, I have not read your book. My apologies. But here's my take on the early pair's failure to produce young for two early seasons. We observed exactly this same thing in a major study of Northern Ohio redtails. We diligently observed 100 redtail nests in a county south of Toledo in the 1970s, carefully recording egg laying, eyass production, and number fledged. This went on for up to three years for many of the nests. Just as we thought from incidental field observations before the detailed field study, redtails more often than not fail in their first one or two nesting attempts.

I recall seeing some of these first nests, and I could actually look up through the sticks and see skylight when the bird was off the nest. There's no way such a shabbily built nest can keep eggs warm enough.

Other times, first year nesters would actually produce an eyass, but the parents would be incapable of properly feeding the young hawks and they died. In summary, many, perhaps most, redtails need to experiment for a year or two to learn how to be effective parents. The two nesting failures you observed were exactly what I would expect in a really tough area such as NYC. The normal redtail food preferences, voles and mice, simply aren't readily available. The pair spent two years trying to figure out what it was going to feed any young that might someday appear. When eyasses did get hatched, after the pair learned to build an adequate nest and learned how to properly sit on the eggs, they had figured out how to exploit the only plentiful and reliable protein source, the common pigeon.

And on that note, I'd really like to learn what these birds are eating. I'm sure pigeons are the major prey species, but are they pouncing on newly fledged squabs that are unable to fly well enough to avoid the big redtail? Or, has the pair honed some new pigeon-catching techniques that overcome the pigeon's innate hawk-avoiding abilities? Whatever, the pair has things all figured out. I'm very familiar with Toledo's and Cleveland's urban peregrine falcons, and they take full adult pigeons in full peregrine stoops (dives). Redtails can't match the peregrine's pigeon-taking dives.

Lastly, don't be concerned about the pair's inability to reconstruct a proper nest this year. Given the opportunity to put a nest back together, it will go up in an inordinately short period of time, seemingly over night. The pair may just putter around with sticks in December and January, but when the days begin to discernibly lengthen in February (the fact the causes the breeding and bonding hormones to exude), the pair will get a nest together so fast you'll wonder how they did it.

I've seen this in the wild. One day I'll see the male trying to drop sticks in the crotch of a big oak or ash. Most of the sticks just drop to the ground. Finally a few stay in the tree. By the end of the day it's apparent that this will be the real nest site. I drive home after marking the nest on my map. I come back two days later to note the progress, and find that the nest appears as though it has been there an entire year. In one or two days it's full sized. The pair may spend many hours in February and early March preparing the nest lining, but the big construction gets done in less than a week, usually in two days or less. This is especially true in old experienced pairs such as Pale Male and Lola.

Hope this info helps. Pass any of it on to anyone you choose.

Sincerely,

John A. Blakeman, licensed falconer, redtail biologist