Saturday, April 09, 2005

Blakeman on the Proliferation of CP Redtails

Donna Browne sent John Blakeman a report of some of the other redtail pairs making nesting attempts around Central Park and its periphery -- the Trump-Parc pair that seems to be incubating eggs high on that building on Central Park Sout, the 97th Street pair that suxccessfully nested in a tree in mid-park last year, the Cathedral of St. John the Divine pair [technically not CP, but near enough] and several other poissible nestings. Here is John's response : At the very end I have one more comment in response to his letter.

Thanks for the updates on the "other" CP red-tails. As you pointed out, the topic of the other CP pairs has not been very publicly addressed. As a raptor biologist I think the CP red-tail story must include all of the red-tails in and near Central Park. As remarkable as Pale Male is, he's no longer the only story. The developing, greater story is how the species itself is colonizing Central Park, and that involves a host of related phenomena, including (as always) prey availability, hunting competition, territory definition and defense, post-fledging hunting experiences for the new eyasses, migration away from NYC, and a bunch of others. It's a classic population biology problem, no longer just the study of a single pair.

I'm not suggesting that continued attention shouldn't be paid to the 927 pair. It should be. But the effects of adjacent pairs and other unmated and immature birds ("floaters") all competing for the same food and nesting territories is the real story. You can see, then, why I'm so interested in learning about the other pairs, too.

I find interesting the several accounts of other pairs failing in first and second nesting attempts, just as Pale Male did. This frequently happens in wild rural pairs, especially, I think, when the involved birds are young and inexperienced, just as in CP. What, then, will be the nesting success rates when there is a larger experienced resident adult population? Right now, except for Pale Male and Lola, all the birds trying to nest are just two or three years old. Things will get interesting when these birds get into their fourth and fifth years. I'm wondering if they won't then take on more typical rural territory sizes and be less accommodative (dismissive?) of nearby adjacent pairs and floaters. Will a population of older adults competing among themselves be less tolerant of either interloping young or nearby adults?

Conversely, is the CP red-tail environment so favorable that when some sort of population equilibrium is attained the birds will be -- as they appear to be now -- a bit social? How will this sort out as the Central Park red-tailed hawk population ages into maturity, when the age curve of the entire population has the shape of established wild rural ones? In the wild, aging adults predominate. Not yet so in Central Park. Right now, the population is bloated with young. Pale Male is the only bird that's been around and knows the entire Central Park score. (And he reads it like a great conductor, from memory, never missing a cue.) The others are still feeling their way through it all.

Wish I lived in New York, so I could watch this first hand. (Well, actually I wouldn't wish to live in NYC - it's an otherwise foreign environment, far too hectic, space-confined, and fast for my laid-back approaches to too many things. But Central Park and its hawks, those I can relate to.) So please be my biological eyes, as you have been. Thanks much.


John A. Blakeman

My additional comment:

John notes a parallel between Pale Male's two unsuccessful nesting attempts and the failures of some of the other CP redtails. But as I see it, their main problems in years past have been the absence of spikes to hold down the twigs at the various ledges they have chosen for their attempts. There were three
unsuccessful nesting attempts in a row on a high ledge on the Annenburg Building of Mt. Sinai hospital. [So these birds must have been older than 2 or 3 years. Don't forget that if, by any chance, these are Pale Male offspring, the first brood fledged in 1995!] The ledge had no spikes, needless to say. In the spring of the 4th year a successful nesting was observed in mid-park -- at 97th Street -- in a tree. Now the 97th St. nest was directly to the west of Mt. Sinai. It is logical to conclude that the Mt. Sinai pair finally gave up and moved to a tree a bit to the west. So their failure was not due to immaturity, as Pale Male's failures in 1993 and 1994 probably were, but were due to the spikelessness of their chosen ledge.

Similarly, the failure during the last two [or was it 3] years of the Trump- Parc pair might be attributed to the smooth ledge they have chosen, rather than to immaturity.