BIRDS AS PILFERERS [Ref]
Pilfering, or petty theft, is one of the less desirable but very human attributes of our race. But it's also pretty widespread in the animal kingdom. Theft as the usual thing is practiced by only a few birds. But when it's a case of petty theft, happening now and then, it is common enough in the bird world. It's not restricted to any group of birds, but may crop up almost anywhere. There's no threat or fight about it usually. The bird, which gets its food by means of the acuity of its vision and the quick co-ordination of its movements with the recognition of its food, sees the food in another bird's possession and just goes up and takes it. Sometimes the food is taken from a larger and stronger bird, an achievement accomplished by audacity, agility, and quickness. A sparrow hawk, that inoffensive little rufous-red falcon that spends most of its time catching grasshoppers, was sitting on a telephone wire holding a small mammal it had caught, apparently about to devour it, when a loggerhead shrike sitting nearby flew straight to the hawk, seized its prey, and made off, leaving the hawk sitting there, apparently dumfounded by the audacity and success of the attack. A case in which the pilfering caused a mild fuss involved an English kingfisher and a dipper. The kingfisher lit above a pool where a dipper was feeding, obtaining food in the pool and bringing it ashore to eat it. When the dipper next came ashore the kingfisher flew down, there was a momentary scuffle, and the dipper departed, leaving its food to the kingfisher, who promptly ate it. Despite this occurrence the dipper allowed itself to lose its prey again before it left, and the kingfisher presumably had to resume fishing for itself.
THEFT NOT RESENTED It is sometimes surprising that this pilfering, when it occurs over and over again, is not actively resented, particularly when the pilferer is a smaller bird. Some of the thrushes are especially docile when they're victimized. Sometimes when American robins are feeding on the ground, house sparrows hop along with them, and when the robin finds a worm the sparrow hops up quietly and boldly takes the worm from the robin with scarcely a protest from the victim. One robin is reported to have been robbed six times, of six worms, one right after the other by a small flock of sparrows while the robin continued to hunt for worms.
The starling, an aggressive Old World species introduced and very successful here, also victimizes the American robin. In one case a starling made four successful raids in five minutes, the robin not attempting to fight or defend its food, but simply moving off a little way and continuing to hunt for worms while the starling waited nearby.
This is not a new trait of the starling, for in its Old World home, in Britain, it has been seen to victimize blackbirds and song thrushes (relatives of our robin). This happened when a blackbird pulled up a worm, a starling flew to the spot, and the blackbird moved away, leaving the worm to the starling. This method of obtaining worms was sometimes used by all the starlings on a lawn where both species were feeding, much to the hindrance in the feeding of both blackbirds and song thrushes.
Gulls have been recorded as snatching fish from mergansers that had caught fish by underwater dives and brought them to the surface to eat. Gulls also follow pelicans, and just after the pelican has completed its plunge and before it can swallow the fish protruding from its bill, a gull may flutter in, alight on the water or even on the pelican's head, and seize the fish. The pelican does not attempt to do anything about it, but accepts the pilfering with stoic calm.
Grackles victimizing ibises seems perhaps the strangest of the whole series of reports. The ibis often attempts to elude the grackles but without success. About Lake Okeechobee, Florida, where ibis are common, they feed largely on crayfish, which they secure by probing the holes made by these creatures. Grackles swarm there, and, on occasion, no sooner does an ibis seize a crayfish than one to four grackles try to secure it. The ibis may take flight and attempt to escape with its prey, but one of the grackles usually gets the crayfish away from it.
Possibly some of these birds are on their way to becoming habitual pilferers, in which such social parasitism is a fixed mode of life. With evolution, if this thieving benefits the species that snatch the food, it may become a usual habit. For habits, like structures, are subject to variations, to selection, and thus to change and elaboration.