Friday, September 08, 2006

Blakeman: the end of a delightful exchange

Red Squirrel in Central Park - January, 2006
Photo by Bruce Yolton

This is really the last of the redtail-vole debate:


I appreciate Chris Lyons’ more detailed elucidation of the 19th century Pennsylvania “Scalp Law” episode, a most important (and tragic) legislative experiment in ecological manipulation. Then, as now, nature isn't always as well-understood or controlled as imagined by those who have the power to create laws and regulations.

I also appreciate and concur with Chris’ views that raptors should be protected because they exist and are natural, not because they might provide some putatively useful ecological service.

Chris makes a broad case for the cumulative roles that all predators play in slowing or rounding off periodic vole population hikes. I don't believe that I suggested that all predation of voles, such as that by weasels, minks, foxes, and snakes (the most common consumers of voles), fail to have any impact. They do. But I specifically contended that red-tailed hawks have virtually no impact, that we shouldn't be claiming that red-tails are essential or important rodent-control agents. Red-tails simply can't eat enough voles each day in their large, multi-square mile hawk territories. . .

But what about squirrels, especially those that declined near a red-tailed hawk’s nest at Fordham University? That’s different. Squirrels don't breed as often as voles, with only one or two litters or so each year, and their populations aren't so large, either. A squirrel makes a nice day’s meal for a red-tail, so it could take seven in a week. A pair could take a over a dozen each week. That could be forty or so in a month. In a small area such as college campus, a pair of red-tails could markedly depress a squirrel population.

And as a falconer who has seen red-tails pursue squirrels up close, I know that squirrels are actually rather easy prey for our big hawks. If the squirrels stay up in the trees, they are relatively safe, able to scoot around a trunk or branch, or duck into thick branches that the hawk can't fly through. In the trees, squirrels are difficult for red-tails to capture. It requires a lot of vertical flying, causing the hawk to quickly ascend into the limbs of the trees. This uses a great deal of energy and unless the squirrel makes an unfortunate mistake, the hawk usually gains nothing for its efforts.

But when a squirrel walks out onto open turf, as found in parks and campuses, the hawk has every advantage. A squirrel out in the lawn is a relatively easy target for a red-tail. It can stoop, or dive, from a nearby tree or building and swoop across the lawn at 60 to 80 MPH. The little squirrel can't run nearly as fast, and may not even see the hawk until too late. From what Chris described, I'm certain that the Fordham red-tails have made a real dent in the local squirrel population. Surely, they can capture and eat those arboreal rodents faster than they can reproduce.

Perhaps there are still as many Fordham squirrels as before, but they may have learned to remain up in the trees, staying off the ground where they are easily pounced upon by the local hawks.

<>And for me, this, too, should be the end of this delightful exchange of thoughts and perspectives on the roles of hawk predation on vole populations. These have been wonderfully thought-provoking concepts and reports...

John Blakeman

[PS from MW]: I've added a source for a quote to the previous post by Chris Lyons. the one John Blakeman is responding to here]