Pre-fledging energy requirements of the nocturnally fed semi-precocial chicks of the Spotted Thick-knee (Burhinus capensis)

Abstract

Studies of pre-fledging growth and energetics in precocial (self-feeding) shorebird species have shown that chicks expend large amounts of energy on thermoregulation and activity. We investigated the pre-fledging growth and energetics of Spotted Thick-knee (Burhinus capensis) chicks, which are semi-precocial (fed by their parents), near Cape Town, South Africa, to determine whether semi-precocial development would reduce the energy expenditure of chicks and enable them to grow faster. In addition, because Spotted Thick-knees are nocturnally feeding shorebirds, we hypothesised that their more limited foraging time (compared with diurnal feeders) would negatively influence growth and energy expenditure of chicks during their spring-summer breeding season. The growth-rate coefficient, resting metabolic rate, peak daily metabolisable energy and total metabolisable energy of Spotted Thick-knee chicks were similar to the values predicted for birds of their size. Therefore, the potential negative impact of nocturnal feeding on growth of chicks may be being countered by reduced chick energy expenditure on thermoregulation and activity owing to parental feeding, and adults potentially extending their foraging time into the day as their chicks become larger. The relative energy requirements of growing Thick-knee chicks were greater than those of precocial shorebird chicks in the same climate of the Western Cape, but lower than those of shorebirds breeding in temperate or arctic zones. The semi-precocial mode of development of Spotted Thick-knees did not result in reduced energy expenditure or faster growth than anticipated for shorebirds in general, but their relative growth was greater than that of precocial species at the same latitude. Therefore, semi-precocial development benefits the growth of Spotted Thick-knees.