ABSTRACT
The evolution of flight in birds provided an ecological advantage in terms of tracking and accessing resources and evading many predators. The almost ubiquitous use of flight in Aves, and the considerable constraints imposed by flight on structure and mass regulation are a likely cause of the highly conserved basic life-history in this class of vertebrate. Fish, reptiles, and mammals exhibit both oviparity and viviparity, but birds are exclusively oviparous and deposit their eggs in a nest, with the necessity for at least some form of parental care. The minimum requirement is incubation, whereby heat is transferred to the developing eggs directly from a parent bird. The eggs then hatch at either an altricial stage where the chicks are born completely helpless — naked, with eyes closed and are even unable to thermoregulate by themselves — or at a more advanced precocial stage where they have downy feathers and are often capable of finding food for themselves. The only group of birds in which there is no direct parental care of the young, and indeed often no contact at all between adults and young, are the megapodes. These birds place their eggs in mounds of rotting vegetation or bury them in the ground in areas where the environmental temperature is suitable for incubation (Jones et al. 1995). In all other avian species in which eggs or hatchlings are provided with care there is a fascinating diversity in who provides that care. In some cases care is provided by large groups of individuals cooperating together to breed, some of whom might be completely unrelated to the offspring (reviewed in Koenig and Dickinson 2004). In another extreme situation, obligate inter-specific brood parasites such as the cuckoos and cowbirds specialize in parasitizing the parental care of other species by laying their eggs in the nests of a variety of hosts (Davies 2000). Whilst cooperative breeding systems and obligate brood parasites pose some very intriguing and insightful evolutionary questions, due to the inherent conflicts of interest between the different individuals they are somewhat exceptional breeding strategies. Over 85% of species reproduce through social
C H A P T E R 8
monogamy, whereby a male and female form a social bond that lasts, at least through the time it takes them to fertilise the eggs, nest, incubate the eggs and raise the young to independence (Lack 1968).
