Part 6

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

There are occasionally discovered behavior patterns of birds that are so unusual as to make one stop and wonder. They are unusual for birds generally, but in a species here and there they are the regular thing. Such is the placing of a shed snakeskin in their nests by some birds.

A bird like the English sparrow, or the road runner, which uses a variety of material coarse or fine, would be expected to use shed snakeskins occasionally, as it came across them. But there are a number of species that seem to use snakeskins regularly in their nests. It would seem that the birds deliberately sought out the skins for this purpose, as though they were as much a part of the nest as the mud in the bottom of a robin's nest or the fresh green grass heads ornamenting the entrance to some weaverbirds' nests.

SOME HABITS BAFFLING I have long since given up thinking that every aspect of a bird's life must serve a useful purpose. Indeed I have already pointed out some definite maladaptations. But usually every type of behavior has a logical origin. By considering its occurrence in various species and against the background of the bird's everyday life some correlations usually can be found.

The list of birds habitually using snakeskins in their nests is short, as follows:

1. Great-crested flycatcher--belonging to the New World flycatchers, breeding in Eastern North America and nesting in holes.

2. Arizona crested flycatcher--a relative of the great-crested variety, with similar habits.

3. Blue grosbeak--an American member of the sparrow family, making an open nest in bushes.

4. Black-crested titmouse--a member of the chickadee family, living in Western North America and nesting in holes.

5. Bank mynah--a starling, living in southern Asia and nesting in holes in banks.

6. Rifle bird--an Australian bird of paradise, making a cup-shaped nest in trees.

7. Madagascar bulbul--making a cup-shaped nest in trees.

LIKE A DECORATION Twenty or more other species of birds have been recorded as using snakeskins more or less commonly, or occasionally perhaps on the basis of availability or of chance. But with the above they're an essential part of the nest. In some of the species the snakeskins are arranged as a rim around the edge of the nest almost as a decoration; sometimes the snakeskins may make up most of the nest.

Now as to possible correlations. The species are not closely related. Except for the two flycatchers the other five represent five different families. The distribution over the world is wide, too: America, Asia, Madagascar, Australia. Various explanations for the behavior have been advanced. It has been suggested that it's correlated with hole nesting, but three of the seven do not nest in holes. The most common theory is that it's to frighten away possible predators by making them think there is a snake in the nest. However, this is not very likely, and, too, one wonders why the birds that use the snakeskins are not frightened themselves. Indeed, one writer, surely not seriously, has suggested that the fright in early life of crested flycatchers at finding a snakeskin in the nest accounts for the upstanding crest in this species!

"BURGLAR ALARM" THEORY Another suggestion is that the snakeskin, by the rustling noise it makes when touched, acts as an alarm bell or a burglar alarm to warn the rightful occupants of the nest when an intruder approaches. This also seems a rather weak explanation.

We are left, then, with the fact that this curious habit has been developed in a few birds, not closely related, that live in various parts of the world and that have very different habits. It is usual with them. A number of others occasionally have this habit.

My first clue as to the proper background against which to solve this habit came when, unpacking a bird collection made in Borneo by curator of anatomy D. Dwight Davis, I took out a bulbul's nest. In its outer edge were flat, weathered leaves that resembled snakeskins. Later, when we received a bird collection from Dr. D. S. Rabor of the Philippines there was a nest of another species of bulbul and this too had flat, dead, weathered leaves in it that looked like snakeskin. When I was in Madagascar, in 1929-31, I had found three nests of the Madagascar bulbul with a snakeskin used in each. Here was a clue. I decided to investigate the nests of the other species of bulbuls of southern Asia and Africa where the family is represented by many species. By considering the snakeskin-using species against the background of the nesting of the other species some correlation might appear.

BOOKWORK This became a library problem at once. I had to look up the earlier reviews of the problem in the ornithological journals, _The Auk_ and the _Ornithologische Monatsberichte_, then in Strong's _Bibliography of Birds_, to make sure that no important papers were missing from my own subject file. Stuart Baker's _Fauna of British India, Birds_ had a large part of one volume devoted to bulbuls, and gave excellent summaries of the nidification of each species occurring there. Bannerman's _Birds of Tropical West Africa_ covered the western part of that continent, and Jackson's and Sclater's _Birds of Kenya Colony_ did the same for the eastern part. For collateral material I looked in Mathews' _Birds of Australia_, Volume 12, Forbush's _Birds of Massachusetts_, and Mrs. F. M. Bailey's _Birds of New Mexico_, and a dozen minor publications.

But it was worth it.

Perhaps my earlier thinking was dominated by the thought that the shed snakeskins had been parts of animals toward which many birds show an antipathy. But it's extremely probable a bird does not recognize the snakeskin as such. Rather to it the shed snakeskin is a strip of thin, flexible material. Obviously it would be used, by chance, by many bird species, such as the house wren, which, in addition to using such natural materials as twigs, grass, and hair, has been recorded as using lead pencils, paper, nails, safety pins, and snakeskins in its nest.

As to the regular users of snakeskin, the snakeskin-using Madagascar bulbul did fit into a pattern. Bulbuls in general make characteristic simple cup nests. Some species use almost any available material. But quite a few species had specific choices of materials: one species' nest had tendrils of vines in its base; another a lining of grass heads of a certain color; another pine needles; another red dead leaves; and the Madagascar bulbul snakeskins.

A SOLUTION There seems to be a tendency for many species to make distinctive nests. They often accomplish this by a choice of material used by few or no other species. What more natural than that one species, being in a country where snakes are common, should hit on shed snakeskins!

To show that the choice of snakeskin as nesting material is an expression of a tendency for each species of bird to make a different kind of nest may not be much of an answer. But it is to an extent. No longer do we say, "Why are certain birds' nests characterized by snakeskins?" Rather we have the broader, more general question, "Why does each kind of bird tend to build a nest different from that of every other kind?" Thus, little by little, we clear away small, vexing questions and resolve them into larger, more general questions. For answers to these we sometimes plan extended work involving field studies, studies of specimens, and books. And sometimes, as we examine a specimen, read a paper, or unpack a shipment, an answer, or at least a clue, springs to our mind.

CO-OPERATION BY BIRDS

The importance of co-operation, contrasted with competition, has assumed increased importance in discussions of evolution, as it has in discussions of human social progress. Co-operation in nature is of various kinds; from the manner in which a forest shelters the squirrel to the manner in which two or more individuals of one species work together for a common object. The working together of two birds to rear a family is so well known an affair that one forgets that it is an example of co-operation, not only in building the nest and brooding and feeding the young, but also in defending the nest and the young.

Sometimes more than one species will join in ousting an enemy. For example, when a cat caught a young robin, recently out of the nest, the parents, in their frantic effort to make the cat release the bird, attracted the attention of another robin and a pair of cardinals nesting nearby in a honeysuckle. All five birds dived at the cat, screaming and pecking it so vigorously that it released the young robin and fled.

EAGLES JOIN EFFORTS More spectacular are some of the co-operative activities of birds in food getting. Bald eagles sometimes feed on ducks. Frequently two eagles may combine their efforts. The two birds may work together to force a black duck from the air onto the water, and when they are trying to catch a diving duck, they much more quickly exhaust their prey by swooping at it in turn. Bald eagles sometimes take water birds too large for them to carry, and then they must flap along dragging their prey on the surface of the water to the nearest shore. On one occasion an eagle dragging a large cormorant ashore was joined by two other birds, and all three took turns in dragging it. When they got it ashore, all three shared it.

Several fish-eating birds co-operate in capturing their prey. "The merganser is primarily a fishing duck ... very skillful and a voracious feeder. It pursues underwater and catches successfully the swiftest fish. Often a party of sheldrakes may be seen fishing together, driving the panic-stricken fish into the shallows or into some small pool where they may be more easily caught," according to A. C. Bent.

When a school of fish approached a flock of white pelicans, the birds suddenly assumed a circular position, surrounding the school. All the pelicans moved slowly but cautiously toward the center of the circle, their heads near the surface of the water or partly submerged and their necks slightly extended. The birds moved in perfect unison, making the circle progressively smaller, ready to engulf their helpless victims at the first opportunity. When all the pelicans were close to the fish, the birds made rapid jabs at the fish and apparently consumed a large number of them. It appeared that every bird got from one to several fish.

13,000 BAND TOGETHER Avocets and, to a lesser extent, the black-necked stilts also band together for co-operative drives on small fry and aquatic insects. Such drives are made in water of wading depth. Instead of forming circles the birds present compact spearhead and wedge formations and sweep the bottom muck with the characteristic back-and-forth side movements of their long bills. As many as 13,000 avocets have been observed taking part in such co-operative feeding projects.

Another striking example is furnished by black vultures observed by E. A. McIlhenny. A three-quarters-grown skunk was wandering across a field. A vulture alighted near the skunk which immediately stopped and raised its tail. Other nearby vultures joined the one nearby the skunk, and when six or eight of them had gathered one suddenly attacked it. The skunk immediately discharged its defensive scent, but without effect, for the vultures attacked in a mass and other vultures circling above joined in until there were probably twenty-five or more around the skunk. With much flapping and croaking, the vultures pulled it about until it was dead, and then devoured it.

On another occasion a black vulture came from high in the air to alight near two full-grown opossums following a narrow cattle trail. The first vulture was almost at once joined by many others until there were probably between seventy-five and one hundred black vultures following the opossums. Suddenly three or four of the vultures attacked and the others joined in. Quickly both opossums were covered with a swarm of hissing, flapping birds, and within fifteen minutes there was nothing left of them but the larger bones and the hides, and these were stripped of every vestige of flesh.

WATCHDOGS AT THE NEST

A savage watchdog outside his master's house helps to protect it. If an intruder comes, the watchdog, if it's the right kind, simply bites him without preliminaries. There's a parallel to this in the bird world. Some birds often have their nests close to wasps' or bees' nests, or in trees inhabited by biting ants. The birds and the ants, wasps, or bees get along without disturbing each other. But when intruders come along the insects swarm out, biting or stinging and driving the intruder away. The insects are protecting their own homes, but one of the results, the protecting of the birds' homes, is just as satisfactory to the birds as if they did it on purpose. This building of birds' nests close to wasps' nests is a common practice with certain sunbirds and weaverbirds, especially in Africa. It occurs too often to be chance. The question naturally arises as to how much the birds understand of it all--do they actually seek out the association? That's difficult to say, but the facts of the association are still there.

Though some of these associations are evidently fairly common and chosen deliberately by the birds--and one can easily visualize how the protection works--field observations as to the natural enemies against which they are effective, and how effective they are, are largely lacking. Usually the records are something like those of Van Rossem for the Giraud's flycatcher in El Salvador, in which he points out that this bird usually nests in certain mimosa trees armed with numerous heavy, curved thorns. These thorns are hollowed out and inhabited by swarms of small but extremely hostile antlike insects, so that the nest is well protected. However, the effectiveness of ant and bee protection against human predation can be seen in the following.

Take the case of Mr. M. E. W. North, who arranged a rope to climb to a fish eagle's nest in East Africa. He had gotten about fifty feet up and was considering going out on the big limb on which the nest was, when he noticed a wild bee on his sleeve. Realizing that he was disturbing a wild-bee hive, and knowing that the sting of these vicious bees can be dangerous, fatalities having been reported, he came down his rope at express speed, crashing through projecting branches and brambles. Reaching the ground, he freed himself from the rope and fled to a safe distance, considering himself lucky to have received only three stings.

On another occasion, again in East Africa, Mrs. R. E. Moreau attempted to reach a hawk's nest to measure the eggs, but when she was up in the tree, savage, biting red ants drove her out.

BIRD GUIDES TO HONEY

In Africa there are birds which lead men to honey. They are called honey-guides and their family name, Indicatoridae, has the same idea incorporated into it. Though there are several species of these small, dull-colored birds, which are related on the one hand to woodpeckers and on the other to barbets, it is only one species, the common or black-throated honey-guide that is well known as a guide to honey.

The traveler in the country may find one of these birds chattering and flying ahead of him. The natives, who know this bird well and favorably will tell the traveler to follow; it will lead to a bee tree. The native, as he follows this guide, gives occasional whistles, as if to encourage the bird. The bird continues, flying from perch to perch, ahead, and chattering noisily. Sometimes it may return to see if the men are following; sometimes it remains chattering on its perch until the followers catch up. Finally the bird will go no farther. It flies about aimlessly and allows one to approach closely. This is the spot. In a hole in the tree trunk, or in the ground nearby the bees' nest is to be found.

When the beehive is opened, and the honey taken, the honey-guide will eat the comb that is left, and apparently it is for this that the complicated behavior of leading of man to the beehive is developed.

Wax of the honeycomb is a usual food of this species, judging by stomach examinations, and one wonders how they get it when man is not about to open the bee trees for them. The birds have no special adaptation for getting into the hives; indeed their only apparent adaptation for this habit is a thick skin, perhaps a protection against bee stings. Perhaps, as has been suggested, other animals, squirrels, monkeys, or honey badgers may unwittingly aid them by opening up bee trees for their own purposes and allow the honey-guides to snatch food for themselves.

An amusing side of the picture is that sometimes the honey-guides may lead the honey hunter to a beehive owned by a native.

There are also records of the honey-guide leading men to big game: leopard or lions. That this occurs is amply documented, but one wonders whether or not this was accidental; the honey-guide leading the way to honey perhaps by accident leads the way past the resting place of one of these big cats so that the man stumbles over the big game and perhaps gets the impression he was led to the animal.

OXPECKERS

The lives of oxpeckers are so linked to those of large, hoofed game or domestic cattle that in West Africa where game is scarce the birds depend on cattle, and their range is restricted accordingly. There the cattle are confined to the higher and more northern areas, free of tsetse flies, from Senegal to Northern Cameroon. Thus tsetse flies help to determine the limits of the oxpeckers' range.

Except for their nesting, which is in holes in trees, and their sleeping, most of their time is spent on the bodies of the larger herbivores. There they run about over the hides and legs of the beasts, like woodpeckers on a tree. They stay remarkably close to the animals, and even ride on them as they travel. The oxpeckers' food is largely ticks, which it gets from the hide of the animal by working over it with the side of its bill, shearing off the ticks with a scissorlike action of its mandibles. But when an animal has sores or cuts or scratches the oxpecker may peck into them, and eat flesh and blood of its host.

Correlated with this unusual and close relationship, a modification in the oxpeckers has taken place. There are only two species, both African, and they are dull-colored, modified starlings. The legs are stout, with curved, very sharp claws for clinging to the hides of animals, and the bill, very sharp at the tip, with the cutting edge of the mandible very sharp to aid in scissoring off ticks.

All the larger herbivores are attended by oxpeckers except the elephant and the hippo, but the favorite seems to be the rhino, and for this he's sometimes called the rhino bird as well as tickbird and oxpecker. The rhino gives the bird its food, and in return the bird provides a service of a value difficult to evaluate. It acts as a sentinel and may warn the rhino of the approach of hunters, for which habit it is execrated by sportsmen.

It would seem that such relationships could have developed only where the supply of big game was large. With the introduction of cattle and other domestic animals it was natural the oxpecker should turn its attention to them. Here the question arose as to the attentions of the oxpeckers being harmful or otherwise to the herds. Mr. R. E. Moreau, formerly of the East African Research Station at Amani, has investigated the problem. He finds that white men who own herds tend to consider the oxpecker a nuisance; Africans tend to consider it beneficial and some African cattle owners object to having the birds killed; the beasts themselves tolerate the birds.

There is the possibility on the one hand of oxpeckers spreading certain cattle diseases that are mechanically transmitted, and on the other hand they may help reduce disease by eating ticks, the vectors of certain diseases. Of course dipping the cattle takes care of ticks on them, and here we see another indirect effect of civilization on bird life. When cattle have been dipped the oxpeckers disappear from the herd. Perhaps it is because there is no longer food for them there; perhaps they get enough of the poison dip left on the beasts' hair to be lethal.

WINGS IN FEEDING

The obvious adaptation of a bird's wings is for locomotion; to fly in the air. It is true that some few birds are flightless, and some like the penguins use their wings for underwater swimming, but this does not spoil the generalization.

Secondary uses, some with special adaptations, occur: the owl at bay spreads its wings wide, with the effect of increasing its apparent size and being more terrifying to a predator. The young bird, begging to be fed, flutters its wings in a characteristic way, and the female, in some of her mating behavior, may also flutter her wings like those of a young bird.

In courtship the wings may play an important part in display. In the Australian rifle bird they are held out, fully spread on each side of the bird like a velvet curtain against which the vivid iridescence of the throat patch stands out more vividly. The argus pheasant has the inner secondaries greatly elongated and ornamented in a fashion recalling the decoration of a peacock's tail and these he spreads to show in his courtship, while the ruffed grouse uses his wings to make instrumental music, his drumming.

Wings in geese and swans may be used in fighting, and tame birds may severely buffet humans who take too close an interest in their young. In the related screamers of South America the bend of the wing is equipped with long, very sharp spurs, which undoubtedly make formidable weapons in fighting.

In addition wings are used in at least three different ways in feeding. The red-tailed hawk may spread its wings as it sits on its prey, perhaps a behavior adapted to help the bird maintain its balance when dealing with struggling prey, perhaps to help smother the struggles of its prey.

The secretary bird of Africa is said to feed on snakes, poisonous and non-poisonous ones, and is said to use its huge wings as shields for its body in attacking them.

But the strangest use of wings in feeding is that practiced by a blackish African heron. In feeding in shallow water it takes a few rapid steps, apparently to bring it within reach of fish it has sighted, then spreads its wings, bringing them forward until they meet, and with the tips of the quills in the water. The head is in the canopy formed by the wings, and apparently it is here under this canopy that the fish on which it feeds are caught. The suggestion as to the correlation that presents itself is that the dark canopy thrown over the fish confuses them and makes them easier to catch.

INSTRUMENTAL MUSIC OF BIRDS