Foraging in precocial chicks of the black-tailed godwit Limosa limosa: vulnerability to weather and prey size

Self-feeding precocial development is associated with high energy requirements and potentially vulnerable to short-term reductions in food availability, yet few studies have investigated development of foraging in precocial chicks and its sensitivity to environmental conditions. We studied time budgets and foraging behaviour during the 25-d prefledging period in the insectivorous chicks of a grassland shorebird, the black-tailed godwit Limosa limosa. Until 8–10 d old, parental brooding was the main determinant of chicks' daily foraging time. Brooding decreased with age and temperature and increased during rainfall. Foraging time increased to 70–90% of the daylight period in chicks older than a week, during which distances of 3–12 km d−1 were covered. Chicks took 98% of their arthropod prey from the grassland vegetation. Prey ingestion rates increased in the first week and slowly declined thereafter, modified by wind speed, temperature and time of day. Chicks in poor body condition were brooded more than chicks growing normally and hence had less feeding time, potentially leading to a negative condition spiral under adverse conditions. However, we found no effect of condition on prey ingestion rate that would preclude recovery when conditions improve. Combining behavioural observations with data on energy expenditure revealed that mean prey size was small (1–4.5 mg), necessitating a high feeding rate, but increased notably after 7–10 d of age. This coincided with a decrease in walking speed, suggesting that chicks fed more selectively. Prey of older chicks approached the upper limit of sizes available in exploitable densities in the grassland vegetation, and this enhances the chicks' sensitivity to variation in prey availability due to weather and agricultural practice