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.
Highlights
Narrow foraging specialization may increase the vulnerability of marine predators to climate change [1]
Results of a recent study suggest that such a foraging specialization might be limited to the reproductive season only, as post-reproductive RLKIs distribute onto the shallow Bering Sea shelf and feed on non-myctophid prey during daylight hours [19]
This study investigated the foraging characteristics of red-legged kittiwakes breeding in the southeastern Bering Sea, using accelerometry (n = 4 birds), GPS tracking (n = 5 birds), and dietary analyses (n = 19 birds)
Summary
Narrow foraging specialization may increase the vulnerability of marine predators to climate change [1]. Seabirds search for and feed on prey at sea by moving long distances from the breeding colony, and are thought to detect and capture prey in a heterogeneous marine environment that has predictable, large-scale oceanographic features (e.g. marine frontal systems [3,4]) Seabirds maximize their foraging efficiency under their morphological and physiological constraints by specializing on prey type [5], feeding method [6], foraging location or zone [7], or diel foraging pattern (nocturnal, crepuscular or diurnal [8,9]). A fine-scale behavioral study on diel patterns, location, and persistence of RLKI foraging behavior during the breeding season, when birds’ energy requirements are elevated [20], is important to better understand their population responses to changing conditions in the Bering Sea pelagic ecosystem
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