DETERMINATION OF CLUTCH SIZE AND THE BREEDING BIOLOGY OF THE SPUR-WINGED PLOVER (VANELLUS-SPINOSUS) IN ISRAEL

The breeding biology of the Spur-winged Plover (Vanellus spinosus) was studied in an agricultural area in central Israel from 1989 through 1 993. The breeding season extended from March to September. The average clutch size was 3.4 eggs and modal clutch size was four eggs. Clutch size declined slightly during the season. Eggs were laid at about two- day intervals. The average incubation period was 28 days, but it decli ned during the season in correlation with increased ambient temperatur es and laying order. In four-egg clutches the last egg was incubated 3 .4 days less than the first. Hatching of a four-egg clutch was asynchr onous and lasted 1.9 days. Field hatchability was 86.4% of all eggs la id. In the laboratory, the highest hatching success (97.7%) occurred a t an incubation temperature of 37.5 degrees C. Field experiments showe d that in four-egg clutches incubation temperature was significantly h igher, incubation periods tended to be shorter (but not significantly so), and hatching success was higher (but not significantly so) in com parison with artificially enlarged five-egg clutches. This lends some, but not unequivocal, support to the hypothesis that clutch size may b e limited by incubation ability. However, females whose clutches were removed upon completion were capable of laying continuously without al tering either clutch or egg size, suggesting that clutch size is not l imited by egg-formation abilities.