Site Consistency in Kingbird Breeding Performance: Implications for Site Fidelity

(1) We used 8 years of data on breeding eastern kingbirds (Tyrannus tyrannus) to test whether breeding success is consistent between years at a site, thus enabling birds to use past reproductive success at a site as a predictor of future success there. (2) Four measures of breeding performance were examined: rate of nest loss to predation, laying date of first clutches, clutch size, and nestling growth rate. The proportion of times that territories were occupied over the 8 years was compared to these measures of performance. (3) The percentage of variation in breeding performance attributable to consistent differences between parts of the study area across years was 20% for predation rate, 43% for laying date, 14% for clutch size, and 15% for nestling growth. These figures were statistically significant for predation, laying date, and clutch size. (4) Territory occupancy by kingbirds was negatively related with both rate of predation and with lateness of egg-laying between parts of the study area. (5) Our data indicate that measures of breeding performance show consistency at sites between years, and thus any tendency of birds to nest preferentially at previously successful sites should be selectively advantageous. Such a tendency appears to be present in kingbirds.