Determination of clutch‐size in the Kentish Plover Charadrius alexandrinus

Abstract

We studied the clutch‐size distribution of Kentish Plover Charadrius alexandrinus in 1991 and 1992 and tested three hypotheses for determination of clutch‐size: egg‐formation ability of females, incubation ability of parents and nest predation. Variation in clutch‐size was small: 71 out of 74 clutches had three eggs (coeff. var. = 7%). Females spent more time foraging (51 ± 6%) pre‐laying and during egg‐laying than their mates (39 ± 5%). However, we concluded that egg‐formation was not constrained by food availability because 77% and 100% of clutches were initiated before the peaks of prey density and of prey mass, respectively. Furthermore, the number of clutches initiated and completed over time was unrelated to prey density. By experimentally reducing and enlarging clutches, we found that enlarged clutches of four eggs took longer to hatch (24.8 ± 0.9 days) than control clutches of three (21.6 ± 0.7 days). Eggs of enlarged clutches also lost weight more slowly during incubation in both years compared with control clutches. No difference was found in the incubation behaviour or weight loss of parents between reduced, control and enlarged clutches. We found no evidence to support the nest predation hypothesis, since neither the proportion of nests predated nor the number of chicks hatched was different between reduced, control and enlarged clutches. The results of this study are most consistent with the incubation ability hypothesis, although the parental ability hypothesis has remained untested.