Seabird

Townsend’s shearwater (Puffinus auricularis auricularis) is an endangered seabird endemic to the Revillagigedo Archipelago. It nested on Socorro, Clarion, and San Benedicto Islands. It was extirpated by the Barcena volcano on San Benedicto in 1952, and there are no recent indications of nesting. Introduced mammals—pigs and rabbits—preyed on them and destroyed habitat at Clarion; shearwaters were extirpated by 1988, and no breeding attempts have been reported since. Our results confirm that Socorro holds the last breeding grounds. We found breeding colonies above 800 m and a minimum population of 1100 individuals. This represents a significant reduction in distribution and population size. Intensive cat predation at Socorro could potentially kill ca. 350 females per season, and sheep progressively destroy nesting areas. Population projections suggest that demographic instability could occur in less than 100 years under severe predation and habitat degradation. Only low predation rates would allow population persistence for more than 150 years in spite of a declining population. Thus, the immediate eradication of all introduced mammals is necessary to prevent the extinction of this seabird.

Breeding success of seabirds critically depends on their foraging success offshore. However, studies combining at-sea tracking and visual provisioning observations are scarce, especially for smaller species of seabirds. This study is the first in which breeding Sandwich Terns were tracked with GPS-loggers to collect detailed data on foraging habitat use in four breeding seasons. The maximum home range of individual Sandwich Terns comprised approximately 1900 km 2 and the average foraging range was 27 km. Trip durations were on average 135 min with average trip lengths of 67 km. Actual foraging behaviour comprised 35% of the time budget of a foraging trip. Substantial year-to-year variation was found in habitat use and trip variables, yet with the exception of 2012, home range size remained similar between years. Food availability, chick age and environmental conditions are proposed as the main driving factors between inter-and intra-annual variations in trip variables. Our multi-method approach also provided geo-referenced information on prey presence and we conclude that future combining of colony observations and GPS-loggers deployments can potentially provide a near complete insight into the feeding ecology of breeding Sandwich Terns, including the behaviour of birds at sea.

This paper is the first comprehensive report of seabirds in the Babuyan Channel, Northern Luzon, Philippines. We compiled photographic evidence of seabird sightings during cetacean surveys in this region from 2000 to 2015. A total of 18 species were recorded, of which two
species were new country records and a further five species were new area records. Our results provide novel knowledge on the distribution of some of these species. They further highlight the importance of the Babuyan Channel to the East Asia–Australasian Flyway, and support the designation of the Babuyan Marine Corridor as a high priority area for conservation and an Important Bird Area in the Philippines. Extensive surveys in the Babuyan Marine Corridor dedicated to seabirds are recommended to continue to identify species and to contribute to the knowledge of seabird distribution and migration patterns.

Zooplanktivorous seabirds as central-place foragers are constrained by the need to repeatedly return to the colony. Breeding within a cost-effective distance from food-abundant foraging grounds may be crucial for successful reproduction. In this study, foraging areas, ranges and habitats of high-Arctic little auks ( Alle alle) breeding on Bjørnøya in the Barents Sea, at the southern edge of their breeding range, were investigated combining GPS-tracking and satellite remote sensing. Birds were expected to forage in areas with productive oceanographic features (cold shelf and frontal zone waters) close to their breeding colony. Contrary to expectation, they foraged in warm waters (sea surface temperature median 6.6 °C), optimal for boreal zooplankton. Little auks preferred shallow shelf waters (mean depth 74 m) characterized by higher chlorophyll a concentrations. Parent birds performed both short (ST) and long (LT) foraging trips, both of considerably longer duration compared to other colonies in more high-Arctic environment. During ST they probably spent more time searching for preferred Arctic prey (dominating in chick diet samples) among abundant Atlantic zooplankton. Long duration of LT resulted from exploring distant cold waters abundant in Arctic zooplankton community. This confirms that little auks are able to respond to various environmental conditions through the plasticity of their foraging behavior without negative consequences for chick survival. To date, observed changes in marine environment have not posed a threat to the ability of little auks on Bjørnøya to feed their chicks energy-rich zooplankton.

The morphometry of 1157 Common Guillemots killed in fishing nets at the northeastern coast of Skagerrak during the last three winters of the 1980s is discussed. Only 10% of the birds were adults (lacking a cloacal bursa). The intra-seasonal variation in size measurements documented for immature birds most likely reflected the continuing growth of young birds during their first winter. The results confirm that the major breeding areas of Common Guillemots wintering in the Skagerrak are found in Great Britain. A suggested decrease in the size of birds during the 1980s could have both methodological and biological explanations, and does not invalidate the earlier findings that this important winter population also recruits birds from breeding colonies in northern Norway (including Bear Island).