Hawk Q & A with John Blakeman

Pale Male with pigeon - 9/5/2011

Photo courtesy of PaleMale.com

Yesterday a reader of this blog, Susan, sent me a question for hawk expert John Blakeman, our frequent question-answerer. Below is her question, followed by his answer:

Q. I've been wondering if we may be seeing evolution at work with regard to urban hawks and their eating preferences. PM prefers pigeons so he is less likely to be poisoned and likely to have more eyasses due to his long life. Some of his offspring may get a preference for pigeon and thus be more likely to survive and pass on the preference. Over time, the pigeon eaters would be more successful and the rat eaters would be less represented in the population. Even if there isn't a gene for pigeon eating (dietary preference), PMs offspring could prefer pigeon just because they were raised on pigeon rather than rat.

Certainly the rat-eating red tails have paid a high price this year and have been removed from the breeding population.

Your thoughts and/or Blakeman's thoughts would be appreciated.

Susan

A.

Susan, y

ou think like a biologist (or are one).

But no, there will be very little genetic selection for pigeon hunting, against rat predation, for the following reasons.

First, Red-tails hunt by sight, preying upon animals that appear to be vulnerable. They clearly do not select prey for taste, only for convenience.

Red-tails are big, and not so fast as typical bird-eating raptors such as Cooper's Hawks and Peregrine Falcons. Red-tails can take pigeons only with stealth, by clever stooping (diving) attacks on pigeons not paying attention on the ground or on nests. Otherwise, a pigeon can easily out fly a lumbering Red-tail.

NYC Red-tails are taking dumb and inattentive and young pigeons.

And they will continue to take rats, as those are their instinctive, preferred prey. Red-tails across their continent-wide range subsist on small rodents.

The eyasses in the nest will not gain a prey preference from an abundance of pigeons being brought there. The fledged eyasses will have to learn to hunt in the first summer, and they will be utterly unable to catch any pigeon then; the hawks aren't clever enough or fast enough to do that when just learning to hunt. They will concentrate on the easiest and most abundant prey, and in NYC it's Norway rats, far and away. Later, as experienced adults, they will learn to take pigeons.

But none of this gets genetically selected. There might seem to be a selective advantage for Red-tails eating primarily pigeons, and avoiding poisoned rats. But it would take many hundreds of generations for this to be expressed as a new, instinctive prey preference, if it ever could be.

The important matter is this. Red-tail populations can withstand rather large annual losses and yet remain viable. Reproduction exceeds deaths of reproducing adults. We just must accept the large losses of immatures.

--John Blakeman