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Birds' Nests and Eggs — Part 2

The European cuckoo, like the cowbird, lays her eggs in the nests of other birds, those of the smaller birds being usually chosen. A certain French writer gives as a reason the fact that the cuckoo cannot lay eggs on succeeding days. How long the interval is has not been decided, but if it is of many days' duration that would be an ample reason for the bird's not building a nest for itself, since the eggs might be stolen were they left unprotected until the full complement were laid. The eggs of the yellow-billed cuckoo are said to be deposited at irregular intervals of from two to five days, and are occasionally found in the nests of other birds. Whether in days gone by they placed their eggs entirely in the care of other birds or whether they will do so in the future is of course a problem, but it is quite possible that some such change is taking place. There are birds who, having laid their eggs, cover them up and allow them to hatch by themselves, trusting to the heat generated by the covering chosen. I know of none of our eastern birds that do this, yet some of them make use of vegetable substance that has heating qualities.

The grebes, for instance, use decayed and damp vegetable matter, while many of our small birds place in their nests woolly stuffs and other non-conducting material, probably to protect the highly sensitive eggs from sudden changes of temperature.

The shapes of eggs show in many instances the forethought of nature. Eggs that are laid on bare rocks and exposed places where little or no nests are made, are generally rounded at the larger end and come almost to a point at the other extremity; this makes it possible for them to be turned by the wind without rolling away; whereas the ovate or elliptical eggs that are found in well-protected places, such as holes in trees, would soon be blown off by a strong wind in such exposed situations.

The ways of birds are difficult to understand. Why should some build in colonies, and others singly but in close proximity, and others again miles away from their kind? The passenger pigeon gives the best example of nest colonies, immense numbers breeding in a very limited area. Prof. H. B. Rooney speaks of a nesting area forty miles long and from three to ten miles wide, where, in 1878, a million and a half of the pigeons were killed for food purposes, while if those that were taken alive and the dead nestlings were included, the number would reach the enormous total of a thousand millions. This is thought to be somewhat exaggerated, but shows what an immense number of birds must have been breeding in this limited space. Some of our small birds nest in colonies; among them the red-winged blackbird and some of the swallows afford the most noticeable examples. The bobolink and marsh wrens also live in scattered communities during the breeding season. Most of the larger hawks select a desirable copse or fairly large tract of woodland as a common home, and it is seldom that another nest of the same species is found within that area. In Florida, where each cypress swamp is usually clearly defined, it is seldom, except in the large swamps, that one finds in each more than one nest of the Florida red-shouldered hawk--a species very abundant throughout the more southern parts of the State.

Some birds return regularly year after year to the same nesting site, even after their nests have been robbed several times. I have known a crested flycatcher to build in the same hole for three years in succession though each set of eggs was taken. Phoebes return with great regularity to the same bridge, building, or rock, where they make one or two nests each season. Some of the owls also use the same hole for many years, and hawks and crows rebuild their old nests, so that each year the nest becomes larger as layer after layer is added.

Most, if not all, birds are governed in their habits by regular rules--from which, however, they occasionally depart just as human beings depart from the rules which seem most generally applicable.

The Wilson's thrush, whose nest is commonly on or near the ground, has been known to build in a hole in a tree. Bob-whites' nests containing thirty-seven eggs have been reported--though these were, of course, not all laid by one hen. The eggs were said to be arranged in tiers, with the smaller ends pointing towards the centre. It is curious to note that if the female bob-white is killed after the eggs are laid, the male bird takes upon himself the entire duty of incubating. This may not be an invariable rule, but a number of instances have been reported by reliable observers. Robins will sometimes build their nests in buildings or bridges with no vegetation in the immediate vicinity of the nest, and mocking-birds have chosen fence rails and other such queer places for their building sites.