HIBERNATION IN BIRDS [Ref]
Not until 1948 did the scientific world have satisfactory evidence that any bird hibernated. True, it was an established fact that sometimes in cold weather some birds, notably swifts and hummingbirds, might become torpid for a short time, but this was not hibernation.
The early literature, of more than a century ago, contained many accounts, some claiming to be firsthand, of birds hibernating. Swallows in particular were reported as seen to submerge in ponds in the autumn. Numbers of them were said to have been found hanging to submerged willow branches apparently sleeping the winter away. When ponds were drained in winter, sometimes swallows were said to have been found buried in the mud, revived, and upon occasion kept alive indoors until the spring. Sometimes slime-covered swallows, evidently just out of hibernation, were reported found in the spring. Swallows were the most commonly recorded, but other species, too, were mentioned as hibernating, such as the cuckoo that shed its feathers and crept into a crevice to sleep away the winter.
Such accounts gradually disappeared from the literature. We can accept none of them. The old records of underwater and also the featherless hibernation of birds must be discarded. The occasional torpidity, in cold weather, of swallows, swifts, and hummingbirds is another matter, and appears to be of sporadic though not common occurrence.
FROGS MISTAKEN FOR BIRDS It is interesting to speculate as to how the old "firsthand" accounts originated. They had certain basis of fact. The first was that swallows were seen flying about in summer. They disappeared in winter. Aristotle claimed they hibernated, in a featherless condition, so there was nothing unusual in seeing them that way. Observation was less critical, and it is probable that frogs from the mud of ponds were mistaken for naked swallows, and perhaps bats, which do hibernate, taken from caves or hollow trees, were also mistaken for swallows.
AN AUTHENTIC RECORD In 1948, and again in 1949, Edmund C. Jaeger, of California, published accounts of a poor-will he found hibernating. This was the first acceptable evidence that such a thing occurs. In a little cavity in the wall of a canyon in the Chuckawalla Mountains of the Colorado desert in California, Jaeger found a poor-will in a state of profound torpidity in December, 1946. He could pick out the bird in his hand, examine it and put it back in the little cavity it occupied without eliciting more than a slight movement of its eyelids. On a later occasion handling it revived it somewhat.
The next winter Jaeger found a poor-will, perhaps the same bird, hibernating in the same niche. Over a period of eighty days, from November 26, 1947, to February 14, 1948, he visited it periodically, examined it, and took its temperature. The body temperature was low, 64°-68° F., compared with more than 100° F. of an active bird; with a medical stethoscope he could detect no heartbeat, and a cold metal mirror held directly in front of its nostrils collected no moisture from its breathing. The body processes were evidently very low. The bird was banded for identification, and in the third winter the same bird wearing the same band was found to have returned to hibernate again in the same rock niche. But on subsequent visits it was missing—perhaps having lived out its allotted span, perhaps the prey of some predator.
SNAKESKINS IN BIRDS' NESTS [Ref]
