Temporal patterns of foraging activities of northern gannets, Morus bassanus, in the northwest Atlantic Ocean

We investigated time allocation and diel rhythms in foraging northern gannets (Morus bassanus). Chick-rearing adults on Funk Island, Newfoundland, Canada, were equipped with different types of data loggers. We found no effects of the devices on the birds' behaviour or breeding success. A total of 25 foraging trips were recorded from 16 birds. Foraging-trip durations (median 13.5 h, range 3.0-39.2 h) showed a bimodal distribution, coinciding with a partitioning of foraging trips into 1- and 2-day trips. Some individuals were consistent in performing either 1- or 2-day trips. During foraging trips, gannets were flying, on average, 44% of the time. Foraging activities exhibited a clear diel rhythm. Flight and diving activity was concentrated during early morning and late afternoon, with reduced activity during midday. Gannets were inactive at night. Flight time between the terminal dive of a foraging trip and arrival at the colony was significantly longer during 2-day trips (94 +/- 22 min; mean +/- SD) than during I-day trips (51 +/- 22 min). Water masses visited differed between 1- and 2-day trips. We could find no evidence for a clear dual foraging strategy, although birds were exploiting more distant waters during 2-day trips, as has been found for many procellariform species.