Sunday, April 10, 2005

Blakeman's Response to My Rejoinder

In response to my comment at the end of Blakemans letter published here under the heading of Blakeman on the proliferation of CP Redtails the raptor expert wrote:

Yes, I've discounted an essential role for the nest-supporting pigeon spikes. I've done this because Western red-tails frequently and successfully nest on bare rock ledges that offer no innate protection from winds and other nest-destroying natural forces. I still tend to believe that until a pair learns to properly line a nest, eggs can cool.
But this will be a wrong explanation when a New York ledge nest gets simply blown away. And your accurate noting of the older age of some of the other failed CP parents negates my contention. If I had to bet on which explanation holds, I think it's yours.
Here's a thought that just came to mind. Are NYC red-tail nests atypical because there are no dead trees from which larger branches can be snapped off and used to construct heavier nests? Looking back, it seems to me that the 927 nest has been constructed of twigs, the diameter of a pencil or less. I seem to recall that wild rural nest have a much larger component of sticks that approach the diameter of one's little finger or larger, real sticks not twigs.. Larger branches can't be snapped off a living, healthy tree by a red-tail. But large, heavy sticks can be easily broken off dead trees, where the bark is already falling away and the wood is brittle.
So here's another unique NYC factor to consider. Has good urban forestry, the removal of all dead standing trees, forced the birds to construct nests with smaller twigs from living branches, which are much less heavy than the larger sticks and branches used in rural nests? If this is so, the pigeon spikes become essential in keeping the twig nest from blowing away. It may be that NYC red-tail nests are not as heavy as wild rural ones because bigger, heavier branches that could be snapped off simply aren't available in Central Park.
Does the absence of dead trees indirectly dictate that NYC red-tails must nest on ledges with supporting pigeon spikes?
And here's a good one. Are pigeon spikes themselves the fundamental reason RTs have been able to invade and persist in NYC? Over the years, have a few errant red-tails attempted to construct building-ledge nests that quickly blew away, leaving the birds stranded (and unnoticed)? Was the introduction of stainless steel pigeon spikes sometime in the 1970s or 80s (I presume) the deciding factor in recent nest successes? Were pigeon spikes the thingamabob that did the job?
After leaf-out in May, look around Central Park and see if there are any dead trees from which larger branches could be snapped off next winter. This could be a major factor in our story. Western ledge nests don't get blown away, and I think they are made of much larger sticks. These may not be available in New York.
John A. Blakeman

Marie's answer:

Dear John,

We've got to get you to visit Central Park! We keep providing more info that you would see for yourself if you just took a walk in the Ramble.

In regard to the absence of dead trees: I'd say that there are plenty of dead trees in the park's woodlands. With the guidance of the Woodlands Advisory Board, of which I am a long-time member, the Ramble, the North Woods, and other small wooded areas are maintained for usefulness to wildlife as well as for public aesthetics. Thus many dead trees are left in place as nesting places for woodpeckers, chickadees etc., just so long as they don't pose a safety hazard to the public. Dead limbs hanging over public pathways are removed , of course. But there are brushpiles around, and many large limbs on the ground in the park's woodlands. There is a deliberate policy to avoid a manicured, horticultural look in these parts of the park.

As for the anti-pigeon spikes as an important factor: I only know of a single site where anti-pigeon spikes have led to a nesting success: Pale Male's ledge at 927 Fifth. I haven't seen any spikes anywhere else. That is the likely reason why all the other attempts of nest-building on various ledges on the periphery of the park have failed, year after year. No spikes.

I often thought that the doctors at Mt. Sinai Hospital should have installed spikes on the ledge where a pair of hawks made nesting attempts three years in a row. I know the doctors were intrigued by the hawks and wrote about them in some hospital newsletter. But those hawks only succeeded last year, when they finally wised up and built a nest in a tree due west of Sinai. [Of course we're not absolutely sure the Mt. Sinai pair are the same hawks as the one who nested in the tree in mid-park around 97th St. But the male we called Pale Male III was a very light-headed bird, and my own hunch is that it was the same pair.]