The Soaring of Birds

Abstract

I HAVE read with much interest Mr. Peal's account of the soaring of vultures, pelicans, adjutants, &c., over the plain of Upper Assam (NATURE, May 21, p.56). Their manner of flight is identical with that of seagulls and harriers over the Canterbury Plains in New Zealand, which is about 150 miles long and 45 wide in its widest part. These birds begin to soar at a height of about 200 feet, and rise in slanting spirals to 2000 feet and under. The gulls are much the most numerous, and flocks of them may be seen soaring nearly every fine day in summer. Sometimes a number assemble, and after going round in circles for a short time, without rising, or rising very little, they come down, the condition of the air being apparently unfavourable for soaring. Whenever I have seen a flock finish an ascent, they all reached the same height, which is consistent with the supposition that they go as high as they can. They never remained at the limit of their ascent even for a short time, but separated, sailing away downward to great distances.