NESTING ECOLOGY OF RESIDENT LOGGERHEAD SHRIKES IN SOUTHCENTRAL FLORIDA

Abstract

I studied the reproductive ecology of Loggerhead Shrikes (Lanius ludovicianus) in southcentral Florida from 1991 through 1993. Pairs were sedentary and defended territories year-round. Completed nests were found from late December to mid-May. Nesting peaked during mid-March with second and third nestings attempted from late March to late May. Sixty percent of all nests were built in blackberry bushes (Rubus betulifolius), but cabbage palm (Sabal palmetto) and wax myrtle (Myrica cerifera) also were used frequently. Mean nest height was 1.6 m and mean clutch size was 4.3 eggs. A mean of 17 days was required for incubation and the mean fledging period was 15 days. Nest failure occurred more often during the incubation than the nestling stage. The majority of nest losses were due to predation and inclement weather (49 and 20 nests, respectively). Mean hatching success was 87%, and 81% of chicks fledged successfully. Nesting success (percentage of nests that fledged at least one young) was 55%, and an analysis of other studies that used this measure detected significant clinal variation in Loggerhead Shrike nesting success, with success rate positively correlated with latitude. Unlike conspecifics in northern latitudes where second broods are considered rare, 96% of breeding pairs in Florida attempted second broods.