DETERMINATION OF CLUTCH-SIZE IN THE KENTISH PLOVER CHARADRIUS-ALEXANDRINUS

We studied the clutch-size distribution of Kentish Plover Charadrius a lexandrinus in 1991 and 1992 and tested three hypotheses for determina tion of clutch-size: egg-formation ability of females, incubation abil ity of parents and nest predation. Variation in clutch-size was small: 71 out of 74 clutches had three eggs (coeff. var. = 7%). Females spen t 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, resp ectively. Furthermore, the number of clutches initiated and completed over time was unrelated to prey density. By experimentally reducing an d enlarging clutches, we found that enlarged clutches of four eggs too k 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 sl owly during incubation in both years compared with control clutches. N o difference was found in the incubation behaviour or weight loss of p arents between reduced, control and enlarged clutches. We found no evi dence to support the nest predation hypothesis, since neither the prop ortion of nests predated nor the number of chicks hatched was differen t between reduced, control and enlarged clutches. The results of this study are most consistent with the incubation ability hypothesis, alth ough the parental ability hypothesis has remained untested.