Question and answer about the anti-pigeon spikes
Many readers have been writing in with various questions about what went wrong with Pale Male and Lola's nest this year. Of course before considering the answers one must remember the first BIG thing that went wrong: Last December the nest and the anti-pigeon spikes that held the nest in place had been brutally removed from the nest site, after ten successful years in place. Any consideration of the causes of this year's failure must begin with that incontrovertible fact.
Many of the questions that arise about this year's nest failure can only be answered in light of the nest's historical background: the fact that it had failed twice before, and then had succeeded ten years in a row. The following letter and my response to it might best explain what I mean by this:
Pamela M. Greenwood wrote:
I have been closely following the saga this year. I very much enjoyed your book.
One quick question. As the pigeon spikes are hypothesized to be the culprit in somehow damaging the eggs, why not remove them? Wouldn't the cradle-like structure hold the nest? It might take a cherry picker, but could the nest be lifted off them, then re-settled on the frame without the pigeon spikes -- or with shortened pigeon spikes? This would have to be done in the fall or winter, of course.
P.M. Greenwood, Ph.D.
Associate Professor of Psychology
David King Hall
George Mason University
Here's the answer I sent her:
Originally, the anti-pigeon spikes were instrumental in anchoring the twigs on the curved ledge. Without them the twigs would have blown off. When the spikes were removed on Dec 7, 2004, it was clear that the birds could not rebuild their nest without the spikes. So...the idea was to find some way to restore them. That was the purpose of the new "structure" -- to be a holder for the crucial spikes. Whether, in fact, the structure itself 0or some other sort of structue might have been constructed to hold the twigs without spikes --that, of course is possible. But of all the various proposals of what to do at that site -- and there were a number of them --- the most reasonable way to proceed seemed to be to try to replicate the old set-up, the one that had been successful for the last ten years.
Your question begins with the assumption that the spikes somehow DAMAGED the eggs. I find this quite unlikely. I don't believe the birds would continue to sit and sit long after the incubation window was over if they were sitting on damaged eggs. It seems more likely that when they build a nest directly on the spikes with no layer of twigs beneath, building the nest from scratch, as it were, something about the spikes there underfoot, perhaps their inflexibility as compared to branches on a tree, or for whatever other reason, something misleads the hawks into thinking that the nest they have constructed there is more substantial than it really is. The upshot: they build too shallow a structure, and incubation does not proceed normally.
There were two previous years, 1993 [the year they built the first nest] and 1994 [after the building removed the 1993 nest] when the hawks had to build from scratch. The nest failed to produce chicks in those years [as I describe in my book] just as it failed this year, another "start from scratch" year. During both those years the hawks sat on the "dud" eggs for many weeks after they should have hatched.
My hopeful belief is that once Pale Male and Lola add a second layer next February, [actually, they are already adding twigs, we've noticed] I believe we'll have a better outcome. That's what happened in 1995, the first year a nest at the Fifth Ave. site had a second layer of twigs.
Perhaps John Blakeman will have a response to this!