Incubation patterns in Harris' Sparrows and White-crowned Sparrows in the Northwest Territories, Canada

Nest attendance patterns during incubation were compared in sympatric populations of Harris' Sparrows (Zonotrichia querula) and Gambel's White-crowned Sparrows (Z. leucophrys gambelii) in the Northwest Territories, Canada, In both species, only females incubated. Females of both species spent similar proportions of their active day incubating, but duration of bouts on and off nests were significantly longer for Harris' Sparrows. Duration of bouts on nests decreased with increasing ambient temperature (T-a) in White-crowned Sparrows. In Harris' Sparrows, duration of bouts on nests decreased with increasing T-a up to 20 C, but increased in length at higher T(a)s. Interspecific differences in incubation patterns may have resulted from the greater risk of egg hyperthermia in Harris' than White-crowned Sparrow nests, because the former are placed in more open locations and exposed to increased solar radiation. In both species, duration of bouts off nests increased with T-a. Increased length of bouts away from nests in Harris' Sparrows may have resulted in part from reduced cooling rates of their eggs, as influenced by the species nest microclimate and greater egg mass. Susceptibility to predation may also have affected incubation behavior. As Harris' Sparrow nests are subject to greater risk of predation than White-crowned Sparrow nests, female Harris' Sparrows could reduce risks to themselves and protect their nests more effectively by taking fewer, lengthier trips to and from the nest and remaining on their eggs for longer periods.