Breeding dispersal patterns within a large Sand Martin (Riparia riparia) colony

Abstract

Colonial birds when returning to breed to a previous location can face different settling options regarding their position in the colony. The decision could be influenced by information gained from the conspecifics’ performance, known as habitat copying. Colonial Sand Martins (Riparia riparia) cannot use evident physical cues when returning to breeding sites, as their nesting substrate is usually renewing completely. We investigated settlement decisions of breeding birds in a unique situation at a large colony along the Tisza River, Hungary, where the nesting substrate was renewed completely in two consecutive years. Breeding birds were ringed at 7-m-long sections of the colony, with totals of 6 sections in 2000 and 20 sections in 2001. Aggregation levels of philopatric birds were estimated by calculating individual distances (expressed in sections) between each recaptured bird. From 1,494 adult birds ringed in the first year, 128 individuals returned to breed in the same colony. The distance to the nearest neighbour in the year 2000 predicted the settlement distance in the next year, indicating a clear preference of breeding closer to the neighbours of the previous year than expected by chance. Age composition had an uneven distribution in the colony, as sections where no clumped resettlement occurred had fewer old individuals than the other sections. Morphological measurements were not clearly different between colony sections. This non-random settlement pattern suggests the existence of breeding groups that could disperse together without being attached to a specific colony site.