Incubation capacity limits maximum clutch size in black‐tailed gulls Larus crassirostris

Abstract

Factors determining clutch size of birds have long been the central issue in studies in life histories. It is assumed that the configuration of brood patches could limit the maximum clutch size. To test this hypothesis we manipulated clutch sizes and measured egg temperature as well as reproductive consequences in black‐tailed gulls Larus crassirostris, which usually lay two egg clutches and have three brood patches. Mean egg temperature in 4‐egg clutches (32.6±1.0°C) was significantly lower than in 2‐egg (34.6±0.4°C) and 3‐egg clutches (34.1±0.4°C), because egg temperature of the coolest egg within a 4‐egg clutch was often substantially lower than the other three eggs. The proportion of eggs hatching from 4‐egg clutches (11.6%) was lower than those of 2‐egg (49.1%) and 3‐egg clutches (52.0%). Four‐egg clutches had longer incubation periods (29.6±1.3 day) than 2‐egg (28.1±1.7 day) and 3‐egg clutches (28.0 ±1.3 day). The results indicate that incubation capacity, which may be determined by the configuration of brood patches, limits the maximum clutch size in black tailed gulls, but not the actual clutch size typically laid.