Potential use of energy expen- diture of individual birds to assess quality of their habitats

Abstract

Since animals show behavioural strategies that are sensitive to costs as well as gains, and because low or reduced energy expenditures are associated with longevity, it is argued that animals may generally seek to reduce living costs. Furthermore, as optimal foragers they may seek to minimise the ratio of costs to gains, so habitat selection should take account of living costs. This leads to the hypothesis that high-quality habitats will be generally cheap to live in. A number of factors could complicate this prediction by elevating costs independently of habitat: the form of the relationship between fitness costs and energy expenditure; breeding-status; indeterminate growth; distribution of individuals within habitat; genetic heterogeneity; predation risk; and pathogens. It is suggested nevertheless that free-living energy costs could provide important information regarding habitat quality where traditional methods are either inadequate or impractical.