Changing winter diet of Thick-billed Murres (Uria lomvia) in southwest Greenland, 1990s versus 2010s

Abstract

Southwest Greenland constitutes an internationally important wintering area for seabirds, including thick-billed murres (Uria lomvia Linnaeus, 1758), but their prey may be affected by the general warming of this sub-Arctic region. We compare murre diet collected in winter in the 1990s and 2010s around Nuuk. Fish made up 36% of the diet (wet mass) and crustaceans 63% in the 1990s, changing to 22% and 78% in the 2010s, respectively. Capelin (Mallotus villosus Müller, 1776) was the dominant fish species, and the smaller contribution in the 2010s coincided with declining densities of capelin around Nuuk. The crustaceans were dominated by two krill species, Meganyctiphanes norvegica M. Sars, 1857, and Thysanoessa inermis Krøyer, 1846. However, M. norvegica was only important in the 2010s (51% wet mass), while T. inermis was dominating the 1990s with 62% wet mass and only 23% in 2010s. The dominance of M. norvegica in the 2010s confirmed our expectations of a gradual “borealization” of this region due to the generally warming sub-Arctic. The smaller contribution of fish in the diet may also support the hypothesis of deteriorating winter conditions for murres. Apart from the diet, plastic was found in 15% of the birds and 53% had parasitic nematods.

Cheap gulp foraging of a giga-predator enables efficient exploitation of sparse prey

“…For a common Antarctic krill type, Euphasia superba , the energetic value has been measured at 3.8 to 5.4 MJ kg −1 ww ( 9 , 74 ). Similar values were found for krill species in Greenland and Iceland ( Thysanoessa raschii and Meganyctiphanes norvegica ) 3.9 to 6.4 MJ kg −1 ww ( 75 , 76 ) and for two other species of krill ( Thysanoessa spinifera and Euphausia pacifica ) 2.94 to 3.8 MJ kg −1 ww ( 21 ). For capelin ( Mallotus villosus, Osmeridae) in Greenland, the energy density is, on average, 4.2 MJ kg −1 ww ( 77 ) but can also vary between sex and season ( 78 ).…”

“…Accounting for the digestive assimilation coefficient, the available energy density per kilo of prey consumed is 3.6 MJ kg −1 (i.e., 4 MJ*0.9). It is important to note that some prey types of humpback whales have a much higher energetic density per kilo [up to 6 to 10 MJ kg −1 ( 75 )] and by targeting these energetic prey a humpback whale would need to ingest less prey mass per lunge and per feeding season (tons) for the same yearly energetic requirement (MJ). If such prey are targeted consistently, we overestimate the prey weights per lunge and yearly-required prey tonnage.…”