Colony Attendance Patterns and Recruitment in Immature Common Murres (Uria aalge)

Abstract

The behavior of immature Common Murres (Uria aalge) two to seven years of age was studied at a colony in southeastern Scotland during two breeding seasons. Immatures tended to arrive progressively earlier in the season as they aged, and were seen at the colony more frequently. Timing of final departure from the colony did not vary between cohorts. Within a day, five-year-old birds spent longer at the colony in the early part of the breeding season compared to later. Immature Common Murres seen at the colony in previous breeding seasons arrived earlier, were seen more often, and were more likely to attempt to breed than birds of the same age that had not been seen before. Overall, recruits invested almost triple the amount of time in colony attendance in the prelaying period than nonrecruits of the same age. Among birds of the same age seen in both 1990 and 1991, those arriving earlier and seen more often in 1990 were more likely to attempt to breed in 1991. The great majority of birds attending clubs on intertidal rocks were two- or three-year-olds. Some two- and three-year-olds, and almost all older immatures, were found on ledges above the breeding area of the colony. Three-year-olds that showed a shift in the course of a season between attending at sea rocks and attending on or above the colony almost all shifted from sea rocks to on or above the colony. Older immatures visited fewer breeding subcolonies within a season compared to younger birds. However, most immatures attending areas/ledges on or above breeding ledges were sedentary, visiting only one subcolony. We recorded 69% of immatures in 1990 and 64% in 1991 primarily attending their natal subcolony. Also, 57% of birds breeding for the first time recruited to their natal subcolonies. These frequencies were greatly in excess of those expected if birds were dispersing randomly. Age did not affect the liklihood of attending the natal subcolony, but in one cohort immatures seen in previous season(s) were significantly more likely to attend their natal subcolony than birds not seen previously.