idea the guarding evoked by the fighting instinct, and supplemented by the instinct to cover or hide the eggs, is responsible for the incubating instinct, which in the modern birds is usually strongest in the female, but is not always confined to that sex.
The possible stages in the evolution of the instinct of incubation in the reptilian ancestors of birds, upon the basis of selection, may have been as follows: first burying the eggs, like the turtle; secondly, burying or concealing the eggs and guarding them, the necessary warmth being furnished by decomposing vegetable débris, as in the alligator, and not directly from the sun; thirdly, laying the eggs and sitting over them to conceal as well as to protect them,[1] in a secluded place, the necessary heat now being furnished by the body of the parent. In the first instance the eggs may not have been concealed, but it seems probable that the instincts of both concealment and pugnacity were contemporaneous, as they were certainly very early in origin.
With incubation is associated a variety of interesting and important instinctive activities, such as rolling the eggs with the bill upon entering the nest, as may be observed in the great herring gull, placing them in position, or stirring them up with the feet, to be seen also in the gull, the domestic fowls and in a great number of wild species; covering the eggs when leaving them, a common practise of the grebes, or standing over the nest and with spread wings shielding the eggs from intense heat, as I have once observed in the least flycatcher; cleaning the nest by removal of broken or addled eggs, which must frequently occur in many species, which I was once fortunate enough to witness from the tent in the least tern on one of the Weepecket islands in Buzzard's Bay. On a very hot day in July one of the eggs, during the absence of the birds, exploded with the report of a pop-gun and blew a small hole in one side. Upon her return this resourceful bird inspected the nest for a moment, and bending down, inserted her lower mandible in the blow-hole; then lifting the heavy egg in her bill, she bore it off slowly over the water and dropped it in the sea. At her next visit every particle which might defile the nest was gathered up and carried away.
The care of the young in the nest (6) embraces a number of fairly well stereotyped, recurrent acts such as (a) the search after prey, its capture and subsequent treatment; thus some birds regularly mince the prey or beat it into a pulp, while others, like the little house wrens, bring moths and various insects to their nest with wings and legs, or with wings alone, removed. Kingbirds have been seen to bruise unruly insects between their bills while at the nest, one assisting the other, and have been photographed in the act, while it is not an unusual sight to
- ↑ It is evident that pythons, which lie upon their eggs, secure in this way both protection and concealment for their offspring.
