Seabirds may have unknowing allies in their hunt for fish. Several years ago, a Japanese seabird specialist now studying the effects of climate change on life in Alaska’s Bering Sea noticed that some birds seemed to target clusters of jellyfish. Last summer, he went back to Alaska and outfitted eight thick-billed murres (Uria lomvia), 45-centimeter-long black and white birds that nest on island cliffs, with the avian equivalent of a GoPro camera and a device that tracked their movements. Half of the resulting videos documented underwater excursions, which included 197 feeding events. In 85% of the birds’ U-shaped dives, they encountered the jellyfish Chrysaora melanaster (pictured above), a common species in that area, on their way back up. About one-fifth of the time, the birds altered their ascent to go after young fish hiding among the jellyfish, the seabird specialist and his colleagues report online in Biology Letters. The more fish hiding under the jellyfish, the more likely the birds were to attack, they note. In recent years, it seems that the number of jellyfish have been on the rise, fueling concerns that their voracious appetites for microscopic sea creatures might have a negative impact on the food web and that their density might alter how fish behave—young fish seek refuge among the jellies’ tentacles, for example—and consequently hamper the ability of predators to catch these fish. But this study shows the opposite can be true as well, with jellyfish creating more opportunities for sea birds. Next, the researchers plan to study murres in years when jellyfish numbers are down.
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