Ecological Correlates of Incubation Feeding: A Comparative Study of High Arctic Finches

We compared the ecology of two high arctic finches to determine which ecological factors might influence male parental roles during incubation. Male Snow Buntings (Plectrophenax nivalis) feed their mates at the nest throughout the incubation period, while male Lapland Longspurs (Calcarius lapponicus) usually do not. We identified and tested seven ecological factors that could potentially explain the difference between these two species; (1) risk of nest predation, (2) nesting synchrony, (3) potential for polygyny, (4) timing of breeding, (5) diet, (6) distance between nest and foraging areas, and (7) nest microclimate. Of these, only predation rate and nest microclimate differed significantly between longspurs and buntings. Buntings nest in rock cavities and suffer lower overall nest predation than longspurs (28 vs. 51%, respectively), suggesting that this factor could influence the occurrence of incubation feeding. However, since male longspurs could feed their mates away from the nest, risk of nest predation can only explain why incubation feeding at the nest does not occur, not why incubation feeding per se is rare in longspurs. Due to differences in nest microclimate on sunny days, eggs cool more rapidly in bunting nests, suggesting that female longspurs can take advantage of solar radiation to warm their eggs and can consequently spend a higher proportion of their time foraging than female buntings. A comparison of female incubation schedules supports this idea; female longspurs spent more total time off their eggs (X = 25.9 min/h) than female buntings (X = 15.9 min/h). We conclude that, of the factors we investigated, the colder nest microclimate associated withhole nesting has been the most important ecological factor influencing the occurrence and high frequency of incubation feeding in Snow Buntings. We discuss the possibility that hole nesting favors incubation feeding in passerine birds in general.