Saturday, August 06, 2005

Q&A about hunting techniques

Photo by Lincoln Karim
August 4, 2005
Fledgling that caught a rat

Mai Stewart sends Blakeman an observation:

<> Did you notice on Lincoln's website yesterday
that apparently fledgling #2 has already succeeded in catching his first rat?? BRAVO!!!!

I think your fears about lack of prey in CP during August may be unfounded -- I've never known CP to lack rats -- even in the dead of summer -- this may be another difference from the country + country RTs. I think the only fears we might have might be about the babies' learning curve re hunting -- and #2 is already ahead of the curve!!

Blakeman replies with some new information about hunting and prey:
Yes, I sure took interest in the photos of the dead rat and the crop-full fledgling. You've noted my previous comments on the importance of voles as sustenance prey in rural areas. There are no voles in Central Park, that's clear. So how do the young red-tails there learn to hunt? Elsewhere, that happens with voles.
It's becoming clear that rats are the missing prey, substituting for the voles of rural areas. Rats are easy for any fledged red-tail to kill. They don't run very fast, and they are big and easy to grab. Their skin (unlike a squirrel's) is thin and easily pierced by talons. Importantly, the hawk gets a kill by merely grabbing the main body part, the thoracic or chest cavity. For a half-grown rat, it's almost impossible for a red-tail to grab the rodent in a non-lethal grip. If it sinks its talons anywhere into the animal, one or two talons are going pierce the lungs or heart. The squeeze alone will suffocate the rat.
Rats -- if they are available -- are better food sources than voles, as they are bigger and easy to kill. I've always presumed, based upon conventional teachings on the Norway rat, that these animals just don't venture out into the sunlight in the daytime, where red-tails could readily pounce on them. I've presumed them to be essentially nocturnal and unavailable to the diurnal (day-active) red-tails. But once again, things in Central Park aren't as I know them elsewhere. Apparently, there are a good number of young, inexperienced rats walking around in the daylight.
I'm certain that any hawk, adult or immature, that kills a rat and just leaves it sit is already in good condition, well fed, and capable of many future kills. It appears that this hawk has now mastered the daily killing of rats, and therefore is well on its way to surviving. If rats continue to be available, the young hawk will specialize on these and remain healthy. Being well fed, it can then experiment with various attacks on pigeons, learning how to capture this difficult prey. Rats can be killed by an outright pounce, with little or no stealth, speed, or surprise. Pigeons, because they can fly so much faster than the hawk, must be taken with clever maneuvers of stealth or surprise.
Although pigeons are the primary prey for CP adults, it looks like Norway rats are the animals that the young must learn to capture to survive in the park. The only parallel for this is in much of the West where several species of ground squirrels (rather rat-sized) are primary red-tail prey species. But most ground squirrels, as I recall, go into aestivation, summer hibernation, so they can't be hunted by young red-tails learning how to survive in August. In most of the West, August red-tails have to learn to capture the ubiquitous voles in order to survive.
Once again, I stress the crucial importance of documenting what Central Park red-tails are capturing. The consistent capturing of food is everything for these birds, whether molting, breeding, rasing eyasses, or learning to hunt for the first time. Rats, I think now, are the keystone species, not pigeons.
Everyone, let us know what prey items are seen, and when. We know about all the pigeons being taken to eyasses on the nest. What, now, are the new fledglings capturing themselves? Looks a lot like rats are the main prey item. When are the rats being captured? Are these all within a half hour of sundown, when the nocturnal rodents are starting to move about? Or, are rats moving across the Central Park landscape in midday, when red-tails really prefer to hunt?
Everything seems different in Central Park. Because of day-active rats, it looks like the 2005 Trump Parc eyasses now have a good chance of surviving. They are learning their hunting lessons well.

John A. Blakeman