Nestling growth patterns and antipredator responses: A comparison between four Acrocephalus warblers

Nestling growth rate was investigated in four Acrocephalus warblers to determine the relative importance of predation and food abundance for chick development. To permit interspecific comparisons, the growth rate constant K was calculated for body mass using logistic conversion factors. Insect abundance at the nest site and predation rates were compared for each species. The results suggest that breeding time window correlates with food abundance and mating system, while both relative predation levels and food abundance influence the nestling phase duration and chick growth rate. Furthermore, chick development measured as the time in days to attain 50% of adult, weight (the growth inflection point) correlated with the onset of the chick antipredator response to jump from the nest to a controlled observer approach. We present a conceptual framework to compare the day of inflection in growth rate as the starting point for the onset of antipredator behaviour (such as crouching) by nestlings. We suggest that growth patterns within the nestling phase, and not necessarily the nestling phase duration, may provide clues to antipredator strategies when correcting for physiological constraints to development, such as in comparisons among closely related species.