from the book, "Our Fascinating Earth"
Almost daily, aircraft somewhere cause fatalities among birds in flight. The worst time, of course, is during the migration season, when the number of birds killed by aircraft undoubtedly reaches the thousands.
There was, however, one newsworthy incident in which aircraft were responsible for saving the lives of several thousand birds. It was in the fall of 1931, when an early blizzard swept over Austria and prevented thousands of swallows from migrating south. As a result they began to die form the cold and the lack of food.
Fortunately Vienna was a home to a number of bird lovers at that time. They managed to charter two aircraft to fly some of the swallows to their winter destination, their migration flight having been canceled on account of the weather. More than 27,000 swallows were collected in and around Vienna and flown across the Alps to Venice. Here they were liberated under sunny skies in a temperature forty—two degrees warmer than that of Vienna when they left. They spent the winter in Italy and prospered.
For humans this was an unusual deed of mercy, for it is too common for us to remain unaware and uninvolved. Birds therefore must occasionally be prepared to apply their own methods of compassionate behavior. Perhaps the crow, whom many would describe as merciless, has some surprises in store for scientific observers. Recent observations have shown that when a flock of crows perceives that one of their number appears dejected, they will sometimes gather around the depressed bird in great numbers. In an attempt to revive its spirits they will render a chorus of continuous, very loud, and lively cawing. This morale—building set of tactics often workes, and the dejected crow appears to respond in a positive manner.
If, during the loud cawing, the dejected bird remains despondent and seems unaffected by the treatment, the flock of healthy crows will attempt to relieve it of its misery. Their method is to attack the unresponsive miserable bird and peck it to death. Scientists consider this to be a form of mercy killing among crows, which sense the depressed one is dying.