COLONY ATTENDANCE PATTERNS AND RECRUITMENT IN IMMATURE COMMON MURRES (URIA-AALGE)

The behavior of immature Common Murres (Uria aalge) two to seven years of age was studied at a colony in southeastern Scotland during two br eeding seasons. Immatures tended to arrive progressively earlier in th e season as they aged, and were seen at the colony more frequently. Ti ming 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 ea rly part of the breeding season compared to later. Immature Common Mur res seen at the colony in previous breeding seasons arrived earlier, w ere seen more often, and were more likely to attempt to breed than bir ds of the same age that had not been seen before. Overall, recruits in vested almost triple the amount of time in colony attendance in the pr elaying period than nonrecruits of the same age. Among birds of the sa me age seen in both 1990 and 1991, those arriving earlier and seen mor e often in 1990 were more likely to attempt to breed in 1991. The grea t majority of birds attending ''clubs'' on intertidal rocks were two- or three-year-olds. Some two- and three-year-olds, and almost all olde r immatures, were found on ledges above the breeding area of the colon y. Three-year-olds that showed a shift in the course of a season betwe en 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 bre eding ledges were sedentary, visiting only one subcolony. We recorded 69% of immatures in 1990 and 64% in 1991 primarily attending their nat al 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 affec t the liklihood of attending the natal subcolony, but in one cohort im matures seen in previous season(s) were significantly more likely to a ttend their natal subcolony than birds not seen previously.