Population size of Humboldt penguins assessed by combined terrestrial and at-sea counts

-The Humboldt Penguin (Spheniscus humboldti) has been reported as declining along its distributional range and has recently been classified as vulnerable. The actual size of the Humboldt Penguin population is still unknown, and a complete population assessment is required. Here we present a study combining both counts of molting birds on land and counts of birds at sea during the molting period. We conducted our study in the Coquimbo Region, Northern Chile, and found 7,619 birds on land and 2,700 at sea, adding up to a total of about 10,300 Humboldt Penguins during the molting season (February 1999). Since these numbers are much higher than all other recent estimates, we emphasize that assessment on land and at sea need to be combined to provide more reliable estimates. Received 20July 1999, accepted 15July 2000.