Saturday, March 31, 2007

John Blakeman on Pale Male Learning From Experience

Pale Male Comes Out and Lola Goes In
Red-tail expert, John Blakeman weighs in on my theoretical comments concerning The Mystery Of Red-tail Survival in Territories with Rat Bait and Poisoned Rats

Your thoughts on rats poisoned with anticoagulant rodenticides and Pale Male’s potential predation of these are extremely incisive. Your training and experience in field biology was evident.

Let me add my comments.

The first point. Red-tails (and almost all other predators) are instinctively attracted to prey animals that do act weird, ones that are staggering, slow to react, or otherwise revealing themselves to be an easy kill.

That, in fact, is the major ecological “function” of predators (to be teleological, which nature isn't). As I've posted earlier and elsewhere, red-tails both in Central Park and out in the wild don't ever control prey population numbers. The continuing numbers of rats, pigeons, and squirrels in Central park attest to that. But they do tend to remove from those populations individuals that are sick, injured, or dumb, thereby contributing to the populations’ overall “health” (properly, their ecological “fitness,” which shouldn't be confused with our personal health and the excess of food we've eaten all winter.)

So, as you've mentioned, a newly-fledged eyass attempting to take its first prey in June or July would eagerly pursue a staggering, poisoned rat out in the open. It couldn't resist.

But, as you've also described (very eloquently without objectionable anthropomorphisms), Pale Male could be deliberately avoiding poison-stunned Norway rats in the ways you've described.

Although one of the great advantages of the bromadialone poison is that rats can't taste the stuff, it is possible that Pale Male was able to detect some untoward or objectionable taste or odor in a poisoned rat he captured and then spit it out. He’s got plenty of other food in Central Park, so he had no hunger-driven impulse to consume the specimen. (He eats like so many in NYC can, with great food variety and in ample quantities, ubiquitously available.) So he could afford to discard a rotting (not yet rotten) rat.

Or, he could have learned not to take staggering rats in the following manner. Falconers (more than anyone else) know intimately how hawks’ almost mysteriously connect and memorize every behavior used to take game. Pale Male knows this when he takes his CP prey. He has learned through memorized experience exactly how the target prey animals behave in every circumstance. Hawks tend to memorize and recall every hunting flight they conduct, learning from each one.

When he might have taken a poison-stunned rat, its behavior was impressed in his brain even before he took the first bite. When he tasted the blood of the rat and detected circulating liver chemicals resulting from the poison, he may have made the connection. Yellow flags went up in his memory. There’s something wrong with staggering rats. Don't bother to capture one.

The lesson may have (probably did) require more than a single poisoned rat. As the product safety information for bromadiolone indicates, a predator is unlikely to consume enough of the chemical from a single rat to kill the predator. But Pale Male may have become sick from a single rat. His brain is perfectly programmed to connect the dots between the sick rat and his discomfort.

You are absolutely correct. Pale Male could indeed have learned not to kill or eat poisoned rats. Even more accurately, you've noted that this wasn't through any human-like intellectualism. Rather, it was through natural selection.

Nonetheless, our beloved red-tails are, in their own curious and interesting ways, true avian intellectuals (the experienced adults, at least).

–John Blakeman
The issues with unenlightened people and with poison here in Wisconsin are sometimes dire. Here are a few words from a wonderful local rehabber, who everyone calls the Bird Lady, and as she wishes to be anonymous....
(The following is not for the sensitive. Some may well want to skip it.)
Hi Donna,
I don't have a lot of experience or data with rodent poisonings, although they occur very often. Farmers use a type of chemical to kill starlings and pigeons, and the predator birds eat the sick birds and are poisoned. I had a bald eagle last year that was so sick, he almost died.
It is hard to find out what the exact culprit is unless you know what you are specifically testing for. And often by the time the bird is found, whatever it was has passed and all you have are symptoms. This past year guys were mixing rodent poison or fly bait with cola and leaving it for the coyotes and raccoons eat. Nasty death, and then the predator birds feed on them and become sick as well, resulting in death.
Comparatively, in some ways, we could count our blessings.
Donegal Browne

No comments: