Parental care in the savannah sparrow

Abstract

The apportioning of parental care by male and female during the nestling stage was studied in the savannah sparrow (Passerculus sandwichensis). Brooding by both parents amounted to 66% of the daylight period during the first 2 days after hatching and decreased to 12% toward the end of the nestling stage. Broods of two received more brooding care than broods of either three or four nestlings during the last 2 days of rearing. We monitored the identity, size, and number of all the prey items (exclusively arthropods) brought by 32 nesting pairs during 628 h of observation. These estimates were later converted to estimates of dry weight of food transported (in milligrams per nestling per hour) by using weight measurements of standard prey items. The number of food deliveries increased steadily with nestling age. Males and females contributed nearly equally in this respect, with some exceptions. Estimates of gross energy carried to the nestlings peaked markedly on days 5 and 6 and decreased afterwards. During this short period, the male contributed significantly more than the female in terms of gross food energy transported. We conclude that the birds can tune their feeding contribution to the nest in subtle ways that the monitoring of food delivery rates alone cannot adequately describe.