Different individual-level responses of great black-backed gulls (Larus marinus) to shifting local prey availability

To grow, survive and reproduce under anthropogenic-induced changes, individuals must respond quickly and favourably to the surrounding environment. A species that feeds on a wide variety of prey types (i.e. generalist diet) may be comprised of generalist individuals, specialist individuals that feed on different prey types, or a combination of the two. If individuals within a population respond differently to an environmental change, population-level responses may not be detectable. By tracking foraging movements of eight great black-backed gulls ( Larus marinus ), a generalist species, we compared group-level and individual-level responses to an increase in prey biomass (capelin; Mallotus villosus ) during the breeding season in coastal Newfoundland, Canada. As hypothesized, shifts in prey availability resulted in significantly different individual responses in foraging behaviour and space use, which was not detectable when data from individuals were combined. Some individuals maintained similar foraging areas, foraging trip characteristics (e.g., trip length, duration) and habitat use with increased capelin availability, while others shifted foraging areas and habitats resulting in either increased or decreased trip characteristics. We show that individual specialization can be non-contextual in some gulls, whereby these individuals continuously use the same feeding strategy despite significant change in prey availability conditions. Findings also indicate high response diversity among individuals to shifting prey conditions that a population- or group-level study would not have detected, emphasizing the importance of examining individual-level strategies for future diet and foraging studies on generalist species.

Rare birds in Slovenia in 2017 –Slovenian Rarities Committee's Report

Summary This report by the Slovenian Rarities Committee presents records of rare bird species in Slovenia in 2017, with some addenda for previous years. The numbers in brackets refer to the number of records (first number) and individuals (second number) recorded between 1 Jan 1950 and 31 Dec 2016. Since 1 Jan 2013, submission to the Committee has been required for 37 additional species, 17 of which are regional rarities. Records of these species are not numbered, since records from previous years were not collected by the Committee. The Barnacle Goose Branta leucopsis was first recorded in Category A, in addition to previous Category D and E records. Other notable observations were the third record of Red-breasted Goose Branta ruficollis, fifth records of Lammergeier Gypaetus barbatus and Pomarine Skua Stercorarius pomarinus, and seventh records of Greater Blackbacked Gull Larus marinus and Red Phalarope Phalaropus fulicarius. The list of birds recorded in Slovenia (as of 31 Dec 2017) contains 390 species (375 in Category A, 6 in Category B, 9 exclusively in Category C; 4 species are both in Categories A and C). Category D contains 7 species, while Category E contains 39, two of which are classified into Subcategory E*. These two categories are not part of the list.