Tuesday, October 16, 2007

more on Lola's kestrel from Blakeman and O'Brien

photo courtesy of palemale.com

James O'Brien writes:
Young kestrels are known for being uncautious by remaining exposed for long periods of time. If you look at the streaking on the breast, this is a young female. I have several pix of young kestrels being picked off by red tails, apparently they take a small percentage of young kestrels...not to worry though, kestrel populations are doing exceptionally well in the city. As always, I have some pix on the blog, http://yojimbot.blogspot.com

John Blakeman adds a note:

Readers should be aware of a significant new lethal element in the lives of American kestrels, at least in wooded and urban areas. Until recently, kestrels were among the most common diurnal raptors in the eastern half of North America. But every recent account shows a declining trend for this formerly frequent species. The population trend line for the American kestrel in many areas is decidedly plunging.
This time, it’s not poaching or trapping, the major killers in the 19th and first half of the 20th centuries. Nor is it bioaccumulating pesticides, which decimated bald eagles, ospreys, and peregrine falcons. Now, it’s another hawk doing the dastardly deeds. It’s “natural,” in a sense.

In recent years, with the termination of widespread spraying of DDT, another fine diurnal raptor has restored itself to high population levels, even probably to numbers never seen before, even in presettlement times.
In the last decade Cooper’s hawks, Accipiter cooperii, have exploded in number. Formerly, as all the older field guides relate, Cooper’s hawks were wary of human disturbance and confined their activities to remote forests and woodlots. The bird eats small birds almost exclusively, and because these prey species had eaten DDT-dazed insects, Cooper’s began to be poisoned. Their reproductive capacities plummeted and these bird-hawks become uncommon.

No longer. The species has erupted. At first, it re-colonized and re-populated its traditional forest habitats. But these habitats became saturated and adults drove off the copious young each year. Most starved, for lack of available prey.
But among all populations (look at the folks walking down a Manhattan or Ohio street), there are always a few “on the edge,” individuals that do not comport to conventional behaviors. So it was with Cooper’s hawks. A few disregarded their innate fears and wariness of humans and they flew right into small towns and started to feed profligately on the abundant, human-provided small birds there. In residential areas everywhere, including the residential boroughs of New York City, people set out bird seed and attract flocks of sitting sparrows, blue jays, mourning doves, and other attractive Cooper’s hawk prey.

Today, Cooper’s hawks breed in local residential neighborhoods, parasitizing the dickey birds on local feeders. Cooper’s hawks are everywhere today.
And sadly, they also pluck off American kestrels. Eyass kestrels, when they leave their nests, are barely capable of flight. A neighborhood Cooper’s hawk simply can't resist the plucking of three or four young kestrels in the first week of their lives.
In recent years, ever fewer young kestrels were able to survive their first summer. Like so many other birds, they became Cooper’s hawk sustenance.

As adults naturally die off, the kestrel population is not being adequately replaced. In my area, an Eagle scout built and erected a number of kestrel nest boxes. Ten years ago, at least half of these would have been occupied in the first spring. These boxes have been up for two years now and not a single kestrel has been seen.

The rise of Cooper’s hawks numbers has resulted in the plummeting of American kestrels where the two species co-exist.

Is this natural? Would this occur if people didn't artificially feed and concentrate song birds at bird feeders? Are backyard bird feeders contributing to the decline of American kestrels. In part at least, this must be so.

Nature is a complex web of interacting forces and processes, not all of which can be anticipated.
–John Blakeman

PS In regard to yesterday's posting of Lola with a kestrel in her talons, reader Karen Anne Kolling commented:

Girls rule.