Avian Nests and Nest-Building as Signals

Birds may signal their condition, health or parental disposition to mates through large nests or intense or elaborate nest-building. The mass, number or elaborateness of nests may exceed their strict reproductive requirements. In several species, courtship rituals include exhibition of nesting materials to mates, and some nests are not used for breeding. Signalling through nests or nest construction may occur both before and after mating and may involve either males or females. Only males appear to be involved in pre-mating signalling, while both males and females may signal after mating. In several species, nest size and nest building activity has been associated with the condition of nest-building males, and females in some cases, while the evidence for parental disposition has been more mixed. Nest defence capacity has also been associated with nest size. In some species, males attract more mates through construction of multiple nests not related to breeding. The benefits obtained by males after pairing through differential allocation of their mates have been found in several species in terms of larger clutches, earlier hatching, biased sex ratios and increased parental investment. There is less evidence of this type of benefits for females. Measured responses of assumed receivers of the information provided by active nest construction may positively affect their fitness. Predators are probably attracted to bulky nests and so nest predation may have selected for concealed nests and for inconspicuous nest building activities, which has probably limited exaggeration of nest-building signals. There is also some evidence that ectoparasites and brood parasites may be attracted to bulky nests. Although signalling through nest construction appears as a plausible evolutionary scenario, much more empirical work needs to be done to demonstrate the relevance of nest-building signals.