Parental care in birds.

Parental care, a usefully imprecise catch-all term for behaviors performed by breeding adults that benefit their offspring, is a popular research area among behavioral ecologists. Across Class Aves, it takes many forms, ranging from warming the eggs during incubation - such that the embryo develops within and eventually escapes from its protective shell - to extensive post-hatching assistance, especially by providing food but also by protecting young from weather and predators (Figure 1). In this primer, I will address the evolutionary forces likely to have shaped the peculiar avian habit of involving both parents in substantial post-fertilization investments, rather than just one.

Multiple aspects of plasticity in clutch size vary among populations of a globally distributed songbird.

Plasticity in life-history characteristics can influence many ecological and evolutionary phenomena, including how invading organisms cope with novel conditions in new locations or how environmental change affects organisms in native locations. Variation in reaction norm attributes is a critical element to understanding plasticity in life history, yet we know relatively little about the ways in which reaction norms vary within and among populations. We amassed data on clutch size from marked females in eight populations of house sparrows (Passer domesticus) from North America and Europe.

Inclusive fitness theory and eusociality.

Arising from M. A. Nowak, C.

Proximate and Ultimate Roles of Food Amount in Regulating Egret Sibling Aggression.

In facultatively siblicidal bird species, the amount of food delivered by parent birds to their young ("food amount") has been assumed to be both an important proximate and ultimate cause of fatal aggression. The proximate "Food Amount Hypothesis" (FAH) contends that sibling aggression will vary inversely with the quantity of food delivered by the parents, presumably mediated by chick hunger. At the ultimate level, food shortages are expected to influence whether the combined effects of aggression and food control by older siblings will be fatal to the youngest brood member(s).

ADVANTAGES AND DISADVANTAGES OF EGRET AND HERON BROOD REDUCTION.

Data from great egrets and great blue herons were used to test a fundamental assumption of Lack's brood-reduction hypothesis, that mortality is brood-size dependent. This was confirmed for the largest brood sizes (4 and 3), which, in egrets, also have the highest sib-fighting rates. Broods of one, however, experienced paradoxically high mortality, especially early in the season.