In most avian species, parents incubate their eggs until they hatch, paying an energetic cost in the process. Incubating individuals are expected to efficiently adjust their investment in incubation according to the thermal demands of their eggs and their partner's contribution to the process. In this study, the effects of ambient temperature, incubation stage, clutch size, and food provisioning by males on the incubation behavior of females, were investigated in the Bull-headed Shrike Lanius bucephalus. We video recorded behavior at 16 nests throughout the 15-day incubation period and established that only females incubate. During the early stage of incubation (5–7 days after completion of the clutch) female shrikes spent more time incubating, with longer periods on the nest (on-bout duration) and shorter periods off the nest (off-bout duration), than during the late stage (9–11 days after clutch completion). Females with larger clutches spent more time incubating than those with smaller clutches. Ambient temperature did not strongly affect female incubation behavior. Male provisioning was positively correlated with the length of time females spent incubating and their on-bout duration. Male provisioning plays an important role in the greater involvement of females in incubation, thereby ensuring normal embryonic development.
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