May 21, 2013
Written by Jack Sanders
Thursday, 19 July 2012 12:41
This, my 946th BirdNotes column, is my last. I thank all the many people who have contributed their sightings, observations, stories, and photographs over the past 20 years — without you, there would not have been a BirdNotes.
We’ve had quite a bit of hot weather this summer. While many of us humans may crank up the air conditioning, turn on the fans, or just sweat a lot, the birds have their own ways of dealing with heat.
Birds have no sweat glands, but recent research indicates they can perspire through their skin. Perspiration cools the body as the moisture evaporates, a process similar to the workings of an air conditioner.
However, birds, like dogs, seem to rely more on “panting” as a cooling technique. On a very hot day, you will notice many birds with their beaks open as they give off excess heat through the lining of their mouths.
According to National Audubon research biologist Stephen W. Kress in his book Bird Life, if the brain temperature of a pigeon increases from 107 to 109 degrees, its breathing will more than triple from 46 to 150 times per minute, allowing it to pass three times more air over its mouth lining.
Some birds, such as cormorants, use another heat regulation technique called “gular fluttering.” This is a rapid movement of the throat that causes air to pass over the throat membranes and reduce body temperature. Many baby birds use this technique.
Vultures and storks sometimes employ “urohydrosis,” the fancy way of saying that they urinate on their legs. As the urine evaporates, it cools the legs — and the bird.
In general, many birds are less active when it is very hot. They seek shade and many also seek water — a dip in a puddle, stream or birdbath. They will also hold their feathers close to their bodies, reducing their insulating effect and increasing the radiation of body heat.
Some birds will even hold out their wings to let the breezes cool them.
Jane R. McCaffrey of West Redding reports: “We have chimney swifts (six at last count) and I’m delighted because I think they are endangered in these parts. Anyway, I’ve seen them fly into our chimney in the late evening, but in between times they never seem to rest. We saw flocks of swifts in France ‘resting’ on slate roofs, and then circling and swirling, much as starlings do. But these swifts seem never to alight on anything.”
Before Europeans settled our area, Chimney Swifts would build their nests on the walls of caves but mostly inside big, hollow trees. These cavities provided safe havens from most kinds of predators.
While the early Americans cut down most of the large trees, they also built big chimneys. Chimneystacks quickly substituted for the trees and became popular nesting sites, so much so that the species became known as the Chimney Swift.
Most modern fireplace chimneys, however, use flues that are too narrow for these birds and some ornithologists believe that may be a reason why the population of Chimney Swifts has been decreasing. Nonetheless, these adaptable birds have taken advantage of other human structures, such as airshafts common in cities, and consequently their numbers in urban and suburban areas are often greater than in the countryside.
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