REPRODUCTION OF FEMALE BOAT-TAILED GRACKLES - COMPARISONS BETWEEN SOUTH-CAROLINA AND FLORIDA

Over 7 yr nesting success, nest mortality and reproductive behavior of female Boat-tailed Crackles (Quiscalus major) nesting in a freshwater impoundment in South Carolina were examined. Most (96% of 1368) nests were built in colonies on cattail (Typha spp.) islands. Average colon y size ranged from 7 to 10 nests; maximum size ranged from 20 to 37 ne sts. Average distance between nearest-neighbor colony nests was 3.5 m. Breeding was synchronized, and at least 50% of all nests in the popul ation were started within 12-16 d of the first. Females used dead (ove rwintering) vegetation for nesting, but colony sites did not appear to be limited. The breeding biology of Boat-railed Crackles in South Car olina differs little from that reported for a population nesting in ca ttail marshes in central Florida, 600 km SW. In each region, 61% of ne sts produced at least one fledgling. Daily mortality rates of eggs wer e slightly lower in South Carolina, but mortality rates of nestlings w ere the same. Unlike in Florida, no difference was found between the s urvival of two-egg and three-egg clutches. In both regions, predation was the main cause of nest loss. Starvation was the second most import ant mortality factor in South Carolina, where it was relatively more i mportant than in Florida. Most predation in South Carolina was by snak es. In Florida rodents were most important. In both areas, predation a ppears to be the main selective force molding females' nesting behavio r.