Reconnaissance for future breeding sites by spotted sandpipers

Abstract

We studied the sex-role-reversed, polyandrous spotted sandpiper (Actitis macularia) from 1974 to 1990 in northern Minnesota, USA. After peak arrival of breeding birds and before peak departure at the end of the breeding season, there were many short-term visitors (transients) to the study site. Stepwise discriminant function analysis (DFA) was used to determine the importance of absolute sex ratio (males/female), sex of the transient bird, number of nests, and number of breeding males and females during the week of visit in predicting whether a visiting bird would return the following year. In addition, multiple regression was used to determine how much variability in the number of transient birds returning in subsequent yearscould be explained by annual values during the year of transience for numbers of breeding males and females, numbers of eggs laid and hatched, and absolute sex ratio. Annual recruitment of foreign adults ranged from 1 to 20 birds, of which 0–56% were seen visiting in previous years. Female recruits were more likely than males to have been observed previously as transients. Twenty-two chicks hatched at our study site returned and bred for the first time more than 1 year after hatching. Of these, 9 (41%) were seen as transients between the year of hatch and breeding. The DFA showed that transient females returned more often than transient males and that the number of transients returning in subsequent years was positively associated with the absolute sex ratio during the week visited. When the sexes were analyzed separately, none of the weekly variables significantly discriminated female return, but sex ratio was positively associated with male return. Regression showed that the number of transient birds returning in subsequent years was positively associated with the number of male breeders at our study site during the year a bird visited. Percentage return the year after transience was positively associated with the number of eggs laid at our study site during the year a bird visited. When sexes were analyzed separately, the higher the number of female breeders during the year a bird visited, the greater the number of males returning in subsequent years, and greater numbers of breeding males were positively associated with transient female return. Based on our results, we suggest that transient birds were searching for better breeding areas for future breeding and that intrasexual competition made this information more important to females than to males.