IMPACTS OF HUMAN VISITORS ON BREEDING SUCCESS AND LONG-TERM POPULATION TRENDS IN ADELIE PENGUINS AT CASEY, ANTARCTICA

Breeding populations of Adelie Penguins Pygoscelis adeliae have been counted at two localities near Casey Station in Wilkes Land, East Antarctica since 1959/60 and 1968/69. At Whitney Point, the breeding population increased from 1122 pairs in 14 colonies in 1959/60 to 4714 pairs in 36 colonies in 1992/93. All new colonies at Whitney Point established on relict colony sites identified in 1959/60. On Shirley Island, the total breeding population has remained at 7770 pairs +/- 10% between 1968/69 and 1992/93, except in 1990/91 when the population peaked at 8719 pairs. An association between the age of a colony and its rate of increase was observed at Whitney Point, with new colonies (those established since 1971/72) increasing more rapidly than colonies extant in 1959/60. At Shirley Island, where most of the colonies extant in 1968/69 have decreased in population, the establishment and growth of 13 colonies has offset this decrease; these new colonies also exhibited the association between age and rate of increase. Breeding success (chicks fledged per nest) was significantly lower for Shirley Island colonies than for those at Whitney Point. Human visitors to Shirley Island from Casey station are believed to be responsible for the observed changes in the distribution and abundance of breeding pairs and for maintaining the stable population by reducing overall breeding success through the disturbance associated with visits.