Nocturnal Foraging by Red-Legged Kittiwakes, a Surface Feeding Seabird That Relies on Deep Water Prey During Reproduction

Abstract

Narrow foraging specialization may increase the vulnerability of marine predators to climate change. The red-legged kittiwake (Rissa brevirostris) is endemic to the Bering Sea and has experienced drastic population fluctuations in recent decades, presumably due to climate-driven changes in food resources. Red-legged kittiwakes are presumed to be a nocturnal surface-foraging seabird that feed almost entirely on deep water Myctophidae fishes. However, there is little empirical evidence confirming their nocturnal foraging activity during the breeding season. This study investigated the foraging behavior of red-legged kittiwakes by combining GPS tracking, accelerometry, and dietary analyses at the world’s largest breeding colony of red-legged kittiwakes on St. George I. GPS tracking of 5 individuals revealed that 82.5% of non-flight behavior (including foraging and resting) occurred over the ocean basin (bottom depth >1,000 m). Acceleration data from 4 birds showed three types of behaviors during foraging trips: (1) flight, characterized by regular wing flapping, (2) resting on water, characterized by non-active behavior, and (3) foraging, when wing flapping was irregular. The proportions of both foraging and resting behaviors were higher at night (14.1 ± 7.1% and 20.8 ± 14.3%) compared to those during the day (6.5 ± 3.0% and 1.7 ± 2.7%). The mean duration of foraging (2.4 ± 2.9 min) was shorter than that of flight between prey patches (24.2 ± 53.1 min). Dietary analyses confirmed myctophids as the dominant prey (100% by occurrence and 98.4 ± 2.4% by wet-weight). Although the sample size was limited, these results suggest that breeding red-legged kittiwakes concentrated their foraging on myctophids available at the surface during nighttime in deep water regions. We propose that the diel patterns and ephemeral nature of their foraging activity reflected the availability of myctophids. Such foraging specialization may exacerbate the vulnerability of red-legged kittiwakes to climate change in the Bering Sea.

Seabirds During Arctic Polar Night: Underwater Observations from Svalbard Archipelago, Norway

“…For example, Swallow-tailed Gulls (Creagrus furcatus) maximize their foraging activity during darker periods of the lunar cycle (Cruz et al 2013) in response to the availability of their prey, which migrates toward deeper water during the day and to the surface at night (a phenomenon called diel vertical migrations; Zaret and Suffern 1976). Red-legged Kittiwakes (Rissa brevirostris) also concentrate their foraging during nighttime since their main prey, lanternfish (Myctophidae), are available at the surface during this period (Kokobun et al 2015).…”

Seabird responses to a changing Bering Sea

“…This Theme Section adds considerably to our understanding of the pelagic ecology of the red-legged kittiwake, an IUCN listed 'Vulnerable' species (BirdLife International 2017) endemic to the Bering Sea. Red-legged kittiwakes remain specialized foragers on oceanic prey during reproduction (Kokubun et al 2015) and associate with deep ocean-basin water areas during wintering (Orben et al 2018). The paper by shows that during 1913 to 2015, warmer oceanographic conditions during the late breeding and wintering seasons have been beneficial to red-legged kittiwakes breeding on St. George Island (Pribilof Islands; Fig.1).…”

Differential responses of seabirds to environmental variability over 2 years in the continental shelf and oceanic habitats of southeastern Bering Sea

“…Hence, location data were available for 5 and 7 RLKIs (20 July-5 August) and 5 and 10 TBMUs (2-12 August) in 2013 and 2014, respectively. Data for RLKIs in 2013 were reanalyzed from Kokubun et al (2015). At the time of recapture, blood samples were taken from the brachial vein of each individual and kept on ice until centrifugation to separate the plasma from the red blood cells, and both were kept frozen until assayed.…”

“…During the study period, we opportunistically obtained adult diets of RLKIs by regurgitation at the time of logger deployment and/or retrieval. Prey species of RLKI samples were identified visually or using otoliths (N = 22 in 2013 and N = 15 in 2014) (also see Kokubun et al, 2015). TBMU chick diet was recorded from direct observation of adult birds (both with and without data loggers) carrying prey items back to their nests in their bill.…”