As a population, Cocos Finches exhibit a broad range of feeding behaviors spanning those of several families of birds on the mainland, while individuals feed as specialists year-round. Although this extreme intraspecific variability occurs as predicted in a tropical oceanic island environment, these specializations challenge contemporary ecological theory in that they are not attributable to individual differences in age, sex, gross morphology, or opportunistic exploitation of patchy resources. Instead, they appear to originate and be maintained behaviorally, possibly via observational learning. This phenomenon adds another direction to the evolutionary radiation of the Darwin's Finches and underscores the necessity for detailed behavioral and ecological studies at the individual level for understanding animal feeding systems and the causation of phenotypic variation.Animals within a population that uses a broad array of food types can feed in diverse ways. In extreme cases, individuals can either use all available foods, as generalists, or specialize relative to other individuals. Biologists predict that generalist populations of feeding specialists will occur under conditions of (i) high food predictability (little or no seasonality), (ii) high food availability and variety, (iii) high population density, (iv) low competition between species, and (v) low territoriality (1-5). Additionally, feeding specializations among individuals within a population often correspond with morphological differences among individuals (1, 3, 6-11).The Darwin's Finches (Geospizinae), a textbook example of adaptive radiation in which striking beak differences among species correspond with ecological differences among species (11-16), provide strong support as well for the correspondence between ecological and morphological differences among individuals within a population (9-11): Within the Medium Ground Finch (Geospizafortis) population on Isla Daphne Major, for example, larger-billed finches are able to crack and eat harder and larger seeds than smaller-billed finches. Darwin's Finch populations with the strongest correspondence between diet and morphology tend also to have the greatest morphological variability, due partly to genetic introgression from other populations (10, 11). The Cocos Finch, the only geospizine found outside of the Galapagos Archipelago, has no known opportunity for genetic introgression from another population, and it has correspondingly low morphological variation (11). This low morphological variability is surprising, nonetheless (17), because the foraging behaviors and resources used by this species span those typical of many different families of birds in adjacent mainland habitats, a circumstance generally believed to promote morphological variability (3,11,18,19 (23,25). The almost invariant finch diets year-round (see below; Fig. 1), the high endemism and low turnover rate of the Cocos avifauna (26), and dietary specialization by the Cocos Flycatcher (20) provide additional evidence for a ...

Stationary and walking tympanate moths (Arctiidae, Geometridae, Noctuidae, and Notodontidae) exhibited discrete behavioural responses to electronically simulated bat echolocation calls. The presence of a stationary response in a given species was strongly correlated with the presence of a walking response in the same species. Some inter- and intra-specific variability in the presence of this behaviour was observed and the evolutionary implications of this variability are discussed. Such behavioural responses by nonvolant moths to ultrasound may protect them from predation by gleaning bats.

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