Where to Forage in the Absence of Sea Ice? Bathymetry As a Key Factor for an Arctic Seabird

Abstract

The earth is warming at an alarming rate, especially in the Arctic, where a marked decline in sea ice cover may have far-ranging consequences for endemic species. Little auks, endemic Arctic seabirds, are key bioindicators as they forage in the marginal ice zone and feed preferentially on lipid-rich Arctic copepods and ice-associated amphipods sensitive to the consequences of global warming. We tested how little auks cope with an ice-free foraging environment during the breeding season. To this end, we took advantage of natural variation in sea ice concentration along the east coast of Greenland. We compared foraging and diving behaviour, chick diet and growth and adult body condition between two years, in the presence versus nearby absence of sea ice in the vicinity of their breeding site. Moreover, we sampled zooplankton at sea when sea ice was absent to evaluate prey location and little auk dietary preferences. Little auks foraged in the same areas both years, irrespective of sea ice presence/concentration, and targeted the shelf break and the continental shelf. We confirmed that breeding little auks showed a clear preference for larger copepod species to feed their chick, but caught smaller copepods and nearly no ice-associated amphipod when sea ice was absent. Nevertheless, these dietary changes had no impact on chick growth and adult body condition. Our findings demonstrate the importance of bathymetry for profitable little auk foraging, whatever the sea-ice conditions. Our investigations, along with recent studies, also confirm more flexibility than previously predicted for this key species in a warming Arctic.

Habitat foraging niche of a High Arctic zooplanktivorous seabird in a changing environment

“…The behaviour and energetics of birds may be directly affected by externally attached devices in two primary ways: (1) by expending extra energy countering both the additional mass and the increased drag; and (2) by decreasing some aspects of their performance, such as speed 81 – 83 . Studies from Spitsbergen and Greenland revealed that little auks equipped with the same type of GPS-logger as in the present study showed longer trip durations 70 , or performed shorter but more frequent long foraging trips 84 compared to unburdened individuals. This bias might have affected the pattern of foraging trips observed in the present study.…”

“…hyperboreus -based energy transfer to C. finmarchicus -based food chain 68 . While adult little auks might be able to cope with suboptimal prey like C. finmarchicus in their environment 69 , the prey selectivity index showed strong preference for breeding birds to provide their chick with large copepods 13 , 70 . Under such conditions, little auks will be forced to search for preferred Arctic prey among very abundant but energetically suboptimal boreal counterparts.…”

Trophic niches of a seabird assemblage in Bass Strait, south-eastern Australia

“…Seabirds are major consumers of marine biomass, feeding on a variety of fish, cephalopods and crustaceans (Ridoux, 1994;Brooke, 2004). The foraging niche of seabirds is influenced by a range of factors, including environmental conditions (Waugh & Weimerskirch, 2003;Amélineau et al, 2016;Jakubas et al, 2017), prey availability (Baird, 1991;Camprasse et al, 2017), morphological characteristics and their influence on flight performance (Phillips et al, 2004;Phillips, Silk & Croxall, 2005;Navarro et al, 2013), and interspecific competition (González-Solís, Croxall & Afanasyev, 2008;Phillips et al, 2008;Kokubun et al, 2016). Competition is thought to promote foraging niche divergence since species occupying the same ecological niche cannot theoretically coexist through time (Schoener, 1974).…”

Energyscapes and prey fields shape a North Atlantic seabird wintering hotspot under climate change

“…They seemed to avoid shelf waters, potentially because at these locations cold water stemming from the Labrador Current [ 48 ] increased their energy requirements. As in summer, they also targeted the edges of the continental shelf such as around the Grand Banks, where upwelling concentrates prey [ 49 ]. A second wintering strategy was also observed: according to the RSF, there was a medium (January) and high (February) probability of little auk occurrence with medium energy requirements when there was little or no C. finmarchicus ( figure 3 c,d ), which suggests that some of the little auks from East Greenland could rely on different prey/food web at the end of winter.…”