Friday, September 02, 2005

Blakeman on Mobbing

Here's another question that fell through the cracks. It was sent in a few weeks ago by Jack Meyer, a Central Park birdwatcher and bird walk leader. I just forwarded it to John Blakeman. Here is Jack's question and Blakeman's answer:
I've just been reading John Blakeman's explanation of mobbing in which he says songbirds only mob hungry immature hawks. Does he include Blue Jays as songbirds? Yesterday I saw Pale Male being mobbed by Jays while he straightened his feathers after bathing in the Gill. It was definitely Pale Male, not a young bird. There were also many Robins present and vociferous, but I did not note whether they were actually taking part in the harassment. I didn't pay a lot of attention to what was going on as I was hoping to find some early warblers along the water, and this was an annoying distraction. Jack
Blakeman's response:

In the broadest sense, blue jays are "songbirds." But specifically, they are corvids, in the family of crows and ravens, and as such are behaviorally rather different from all the other passerine ("perching") birds. >From time to time, blue jays will mob any sitting red-tail. Most passerines (birds in perching bird families) mob red-tails only in the spring and early summer, when they are trying to defend nearby nestlings and fledglings. As you've noticed, blue jays are a bit more maniacal and will pester a sitting red-tail much laser in the season, perhaps even into the fall.
I've seen this several times, just as you've described, and I can't explain this mobbing. But who can explain any of the often sordid behaviors of the corvids. This ornithological family is famous for strange, albeit clever behaviors.
The jays were "aware" that Pale Male had doused himself in his bath and therefore couldn't fly with any alacrity. In these conditions they were free to pester the sitting hawk. But they were probably also intelligent enough to refrain from such carryings on when the hawk was in flight with dry feathers. Experienced red-tails have a wonderful way of luring pestering birds within the range of their lightning-quick talons when being pestered in flight.
Here in Ohio, in a major red-tail field study, we were perplexed at finding the red epaulet feathers of male red-wing black birds in most red-tail nests. How can a red-tail capture so many red-wings? Red-wings are robing-sized and very agile in the air. They should easily avoid capture by the large, somewhat lumbering red-tail. Then, we saw how the Ohio red-tails so easily and frequently captured the male blackbirds.
Each morning, in June and July, the resident male red-tail would fly off and begin his daily hunting routine, perching at a spot for a half hour or so, looking around for something to capture, and then moving on a half mile away to another hunting perch. As the red-tails moved from one hunting perch to another, they often flew over large hay or alfalfa fields, and each of these had a breeding population of 10 or 20 nests of red-wing blackbirds. Male red-wings have harems of five or ten females, each with a nest. As our red-tails flew over these hay fields, the resident red-wing male would ascend and start mobbing the passing hawk. On the first day, the red-wing stayed rather distant from the hawk, diving at it no closer than 10 or 20 feet.
On the hawk's hunting rounds the next day, the bird flew over the same hay field. On the second pass, the red-wing male was emboldened at his "success" in driving off the intruder on the previous day. By the end of the week, the blackbird really began to defend his females and their nests by physically attacking the back of the flying hawk as it passed over the harem of blackbird females. All during the week, with each day's closer approaches by the blackbird, the hawk never changed his behavior in the least.
Then, finally, as the male blackbird had done on several previous days, it again physically attacked the big, lumbering hawk as it passed 30 feet above the red-wing nests. But the red-tail had been setting things up all week, luring the blackbird ever closer each day. On this final, fateful day for the red-wing, the hawk flipped over on its back and in an instant grabbed the red-wing out of the air. The hawk diverted from its daily hunting route and took the captured blackbird back to its nest.
The red-tails learned to sucker the mobbing red-winged blackbirds ever closer in their daily flights across the hay fields, allowing the testosterone-crazed red-wings to think that their ever-closer mobbing behaviors had caused the hawks to fly out of the fields. In truth, the hawks were cleverly luring the blackbirds into easy killing range.
Your bluejays are more intelligent than the Ohio red-winged blackbirds, and they aren't so likely to attack or mob a free-flying red-tail. But if one would become inattentive and get too close, it might become a culinary diversion for Pale Male.

John A. Blakeman