Thursday, July 21, 2005

Hawks on the Highway: John Blakeman

Another question for John Blakeman, this one from Kentucky, and his answer:

Dear Marie:

John Blakeman writes that adults drive off the first year birds. Why
then does it seem that in my suburban area, the birds I see sitting on
the light poles over the expressway and hunting in the medians are
almost always juveniles, as judged by their by their plumage? Are the
adults too smart to hunt on the expressways, leaving this dangerous
practice for the younger ones, or perhaps all the expressway foragers
are killed so that none survive to be adults? The grassy medians and
shoulders can certainly entice a hungry immature bird but a dive toward
prey can be disastrous if ill-timed with traffic! I would be interested
in Mr. Blakeman's opinion on the expressway hunters.

Thank you!

Sally Seyal, Prospect, KY

Here's the reply. I've emphasized a phrase or two of particular relevance to Central Park:

No, both immatures and adults love to hunt from perches along expressways. The grassy margins typically have high populations of voles, the favored food of red-tails.
The simple answer is that the immatures you see along your expressways just happen to be in areas that aren't adult territories. This is particularly true in suburban areas. Central Park notwithstanding, red-tails still prefer to breed in rural or wild areas, not in suburbs or cities. Consequently, immatures who find the voles in your areas are delighted to find spots that resident adults don't claim.
But someone (intelligently) is going to note that they saw both adults and immatures sitting rather closely together, apparently hunting in the same area. I must be careful in stating that adults drive immatures out of their territories. Generally, this is the case. But red-tails being red-tails, there is almost always and exception to very general rule. From time to time an immature will be seen parked right along with a pair of adults in August and September. Why? Probably because the local territory has an exceptionally high concentration of food, so the parents or adults don't perceive the youngster as a competitor for food. (This may be the case in Central Park.)
We know that in late fall and winter, generally after the migration, there can be large concentrations of red-tails of all ages in concentrated, local areas that appear to have large local populations of food. At so-called "game farms," where artificially large populations of captive-reared pheasants are set out for hunters, red-tails of all ages can concentrate in these areas.
As with so much of red-tail biology, availability of food is everything.
If you haven't, try to make mental (or written) notes on the birds you are seeing on your expressways. You will find that red-tails, for periods of anywhere from just a few days, on up to almost months on end, will tend to park at the same locations, at the same time of day. You will begin to note the same birds each day in the same spots, barring abnormal weather.
The blond-headed red-tail that I reported here in Ohio a few weeks ago, a Buckeye Pale Male, was seen sitting on exactly the same fence post at the same time of day for two weeks. He had found a local concentration of voles and exploited it for some time. I looked for him yesterday at the right time and spot, but he was gone. He's changed his daily hunting routine and is perched somewhere else now.
You raised the question of red-tail safety when hunting along major highways. I've never seen an adult killed by a vehicle strike. Adults seem to pretty much understand the rather consistent behavior of motor vehicles. Immatures out on their first hunts in July and August, when powered by the hunger of the season, aren't so competent. They will dive off a hunting perch directly at a distant mouse or vole and pay no attention at all to oncoming traffic. But because their vision includes both narrow-angle telescopic views, along with a wider landscape perspective, most often the immatures will veer away from an approaching car or truck at just the last moment. But not always. Vehicle strikes are a small, but noted hazard to inexperienced immatures.
Hawks must be able to note the position of approaching objects while in flight. The Central Park red-tails, from time to time, must be aware of the location and approach -- often at exceptional speed -- of peregrine falcons. A peregrine dropping out of the sky at 200 mph closes quickly on a red-tail drifting around at 30-40 mph. When dove upon, a red-tail better know how to evade the much quicker peregrine. The same mechanics apply to cars and 18-wheelers humming down a freeway. Fortunately for the red-tail, these wheeled predators generally fly only just above the concrete, seldom in the grass, and never in the sky. By September, most red-tails get it figured out. But I've found a few red-tail roadkills, always in July and August.
In much of North America, particularly outside of the traditional cattle ranges of the West, there just isn't much pasture or meadow available anymore. Voles don't live at all in forests, and have low densities in brush lands. They require open-sky grassy environments, and the thousands of miles of Interstate and expressway rights of way are now prime red-tail habitats, as you've seen in Kentucky. Highways are major survival factors for red-tails and kestrels, who use them for the same reasons.

John A. Blakeman