A method to assess population changes in king penguins: the use of a Geographical Information System to estimate area-population relationships

During the last decades, king penguin (Aptenodytes patagonicus) populations have been reported to increase throughout most of their breeding range. In this study, we compared the results obtained from direct counts of incubat ing king penguins with the results yielded by the estimation of the change in area occupied by breeding birds at the Ratmanoff king penguin colony at the Kerguelen Islands. The area of the colony was determined using a Geogra phical Information System with a georeferencing extension on aerial picture s taken in 1963, 1985 and 1998. Individual king penguin were counted on the same pictures or pictures taken on the same day. The overall population in crease between 1963 and 1998 was 733% while the colony area increased by 67 7%. This study indicates that monitoring change in colony size is a good in dicator for detecting and monitoring large population changes in king pengu ins, in particular for remote colonies. The discrepancy between the two res ults may be from two different kinds of bias. Firstly, there could be a pos sible error in the estimation of the area occupied by the colony resulting from the georeferencing of oblique pictures, and secondly, the density of k ing penguins may also change with population number. This method, which onl y requires high-altitude pictures, also reduces the possible disturbance to breeding made by low- to medium-altitude flights.