Introduction

THE object of this book is to describe the biology of nest-building behavior among birds. A nest is a special construction forming a bed or receptacle in which the eggs and young develop. Nests occur throughout the animal kingdom (N. Collias and Collias 1976), and are designed by evolution to help the parents meet the needs of their young. The type of nest built gives important insights into the life of each species, since nests focus the essential requirements of animals for reproduction. Nests are therefore very relevant to the science of ecology if we define ecology as the study of the relationship of living organisms to their environment.

F. H. Herrick (1911), one of the early pioneers in the scientific study of nests, or "caliology" as it was then called (C. Dixon 1902), stated that "it would be difficult indeed from the standpoint of the student of instinct and behavior, to find a more unsatisfactory class of scientific literature than that which deals with the nests of birds." The picture is now changing with the growing realization that nests provide clues to real and significant ecological relationships. Particularly during the last ten or fifteen years a large and important body of literature has grown up.

Bird nests include the best and the most highly evolved nests known among vertebrate animals. In relation to the nest there are two main types of birds, nidifugous ("nest fleeing") and nidicolous ("nest dwelling") birds (Nice 1962, Welty 1975, Skutch 1976). Nidifugous species have precocial young, which leave the nest soon after hatching. Examples are chickens and ducks. The young hatch covered with down, their eyes are open and alert, they can walk the day they hatch, and they are soon able to feed themselves. Nidicolous species generally have altricial young, which hatch in a helpless state — unable to stand, naked or nearly so, and with eyes closed. The young are completely dependent on the parents for food, comfort, and protection, and are unable to leave the nest for days, weeks, or even months, depending on the species. Nidicolous birds build the best nests among birds, and include the great majority of species. The most important examples are the passerine or perching birds, which comprise the largest order (Passeriformes) of birds and include more than half the living species.

Nests are of particular interest to the student of animal behavior. Nest-building behavior has traditionally been accepted as a classic example of instinct, a vague term that has served as a convenient label for species-typical behavior, without implying necessarily anything as to the causation of this behavior. The type of nest built is as much a property of a species, as is its behavior, appearance, morphology, or physiology. When a bird builds a nest it makes a more or less permanent record ("frozen behavior") of its behavior as related to its evolution.

Plan of Treatment

One can relate some important problems in the life of birds to the types of nests they build. These problems are the subjects of the various chapters and determine the general organization of this book. Comparisons of different kinds of nests (chap. 2), particularly within a group of related species or genera (chap. 3), give clues about the evolution of nest-building behavior. Sex differences in nest-building behavior are related to the type of mating system characteristic of the species and to the ability of a bird to attract and keep a mate (chap. 4). In male birds of some species the ability to manipulate materials has even become specialized in evolution and has been redirected solely to obtaining mates instead of to the task of building a receptacle for the eggs and the young (chap. 5).

Adaptation to the stress of the physical environment helps explain the nature of the nest site (chap. 6) and the type of nest (chap. 7). The diversity of competitors also helps explain the diversity of nest sites and construction in different species (chap. 8), while the form and strength of nests is often closely related to the need for security from different predators (chap. 9).

Just how a bird builds its nest (chap. 10) can be analyzed according to various sign-stimuli governing the acts and sequences of building behavior (chap. 11). The "play nests" built by immature birds of some species differ from the finished products turned out by the adults, and a comparison of the building behavior of young birds with that of mature birds gives an insight into the development of the ability to build (chap. 12). Changes in internal factors, particularly in the levels of secretion of different hormones, interacting systematically with behavioral factors, lead to the onset, increase, decline, and termination of nest building and of nesting motivation (chap. 13).

Finally, there are problems related to gregarious nesting (chap. 14). Many birds breed in groups or colonies. The degree of crowding of nests can be related to such problems as the distribution of food resources, predation, and stresses imposed by the physical environment. Gregarious nesting also increases the competition within the species. These negative aspects are balanced against the advantages of gregarious nesting, which include social facilitation of nest building and of breeding behavior.

There are about 9,000 known species of living and recently extinct birds in the world, variously classified in some 20 to 29 orders and 148 to 171 families (Mayr and Amadon 1951, Storer 1971, Welty 1975, Van Tyne and Berger 1976, Bock and Farrand 1980, Cracraft 1981). Appendix One gives a list of orders and families of the world's living birds with the general types of nests they build. Scientific and common names of birds referred to in the text are listed in the index.

Most birds are small, and in general small birds build the finest nests. In the Old World, the weaverbird family (Ploceidae) and the Old World warblers (Sylviidae), and in the New World, the tyrant flycatchers (Tyrannidae), ovenbirds (Furnariidae), and the orioles, caciques, and oropendolas (Icteridae) are noted for the great variety of complex nests they build.

Appendix Two lists some references that have excellent photographs of many kinds of nests. A selection of photographs showing some of the main types of nests is presented in the next chapter, especially in...