Changes in lipid and protein reserves and in diet of breeding House Sparrows

Abstract

We collected House Sparrows (Passer domesticus) around London, Ontario, weighed their protein and fat reserves, and determined their food habits and egg production to test the effects of reserve levels on the timing of egg formation and the control of clutch size. Although consumption of high-protein foods was apparently related to insect availability, females consumed more high-protein foods than did males, especially during the laying period. Before egg production began, protein and fat reserves of males declined but those of females were constant. After egg production began, reserves of males remained constant through postreproduction. Neither protein nor fat reserves were accumulated by females before egg formation began, suggesting that an elevated threshold level of nutrient reserves was not necessary to commence egg formation. Protein reserves of females did not decline during egg production; fat reserves increased just before the first ovulation and declined rapidly thereafter. Neither fat reserve levels on the first day of ovulation nor the decline in fat reserves thereafter were related to clutch size. Postlaying females had, on average, enough fat reserves to produce an additional egg. We conclude that although female House Sparrow use fat reserves during egg laying, their clutch size is not controlled thereby.