Consistent foraging routes and benthic foraging behaviour in yellow-eyed penguins

Yellow-eyed penguins Megadyptes antipodes seemingly forage at discrete marine locations over the continental shelf, where they are believed to feed predominantly at the seafloor. Such behaviour would distinguish them from most other penguin species that generally employ pelagic foraging strategies. From 2003 to 2005 we studied the foraging behaviour of yellow-eyed penguins breeding near Oamaru, New Zealand. We used 2 types of data loggers: GPS loggers recorded geographical position and dive depth at set intervals, while time-depth recorders (TDRs) recorded only dive depth. The penguins performed day trips (range: 12 to 20 km from the coast) or shorter evening trips (range: < 7 km). Consecutive foraging trips of individuals revealed remarkably consistent foraging routes. Birds travelled along similar-at times congruent-paths, markedly changed course at distinct locations, and revisited certain locations on separate trips, indicating skilful navigation. Three trip stages could be distinguished on one-day trips. During the outgoing (seaward travelling) and incoming (shoreward travelling) stages the birds followed linear courses. These stages were separated by a period of midday activity in which birds exhibited higher dive effort and often tended to stay within confined areas. The diving behaviour revealed an exclusive bottom-foraging strategy, with 87% of all dives being benthic dives; the majority of non-benthic dives occurred during the last 2 to 3 h of the trip, indicating primarily travelling behaviour. Furthermore, yellow-eyed penguins employ benthic dives not only when feeding but also frequently when travelling. We suggest that benthic dives might facilitate navigation and, consequently, account for the consistent foraging patterns of yellow-eyed penguins.