Foraging effort does not influence body condition and stress level in little auks

Abstract

In conditions of deteriorating food availability, seabirds may maximize their breeding success by increasing reproductive effort, which compromises body condition, stress level, survival, and future reproductive success. We studied a small planktivorous alcid, the little auk Alle alle, in 2 breeding colonies in west Spitsbergen, Norway (Hornsund and Magdalenefjorden) with contrasting oceanographic conditions (Arctic and Atlantic environments, respectively). We hypothesized that the chick diet composition and parental foraging effort differs between these colonies, which results in intercolony variation in body mass and stress level of both adults and chicks. We found differences in sea temperature and salinity (both lower in Hornsund) and the abundance of Atlantic copepod Calanus finmarchicus (3.6 times less abundant in Hornsund) between foraging areas. Birds from both colonies foraged selectively on Calanus glacialis CV. Composition, total biomass and energy content of food loads were similar in both colonies, though food delivered to nestlings in Magdalenefjorden was more diverse. The frequency of feeds was also similar in both colonies. Parent little auks in Magdalenefjorden, however, performed longer foraging trips than in Hornsund (medians 183 vs. 124 min). Longer foraging trips suggest that these birds traveled longer distances to find abundant prey at the marginal sea ice zone and/or spent more time foraging close to the colony but in poorer foraging areas. Despite increased parental efforts in Magdalenefjorden, body mass and stress levels of adults and chicks were similar in both colonies. This suggests that little auks from northwest Spitsbergen did not reach a threshold requiring prioritization of self-maintenance over chick provisioning.

Foraging by little auks in the distant marginal sea ice zone during the chick-rearing period

“…4). The results conWrm earlier suggestions that (Kwasniewski et al 2010;Jakubas et al 2011;own unpublished data), which occurs in large concentrations only close to the sea ice (Hop et al 2000(Hop et al , 2006.…”

“…Also, observations of individuals not burdened by loggers show that little auks in Magdalenefjorden spent more time foraging than the birds from Hornsund (Kwasniewski et al 2010;Jakubas et al 2011). This implies that little auks from Magdalenefjorden spent more time feeding at suboptimal foraging grounds or extended their foraging range.…”

The effects of loggers on the foraging effort and chick-rearing ability of parent little auks

“…Quite extreme predictions indicate that a strong reduction in sea ice coverage in future years might induce the breeding failure of the whole Spitsbergen population (Joiris and Falck 2010). Little auks exploiting less favourable foraging grounds may increase their foraging effort to a certain extent (Jakubas et al 2007;Kwasniewski et al 2010;Jakubas et al 2011a). However, those extra costs may have detrimental effects in the subsequent breeding season, appearing in the reduction of future survival and/or breeding attempt .…”

“…Predicted shift towards a warmer climate scenario is likely to favour smaller boreal zooplankton species, with a lower energy content compared to the copepods little auks are currently feeding on Stempniewicz et al 2007). This may have a negative impact on the little auks' time and energy budgets, feeding frequency, breeding success and range of distribution Jakubas et al 2011a). Based on sea surface temperature modelling, Karnovsky et al (2010) predict that many little auk colonies in the Nordic Seas will face a shift towards a zooplankton community dominated by small Calanus finmarchicus by the end of the twenty-first century.…”

“…Owing to the high cost of locomotion, both in the air (flapping flight) and in the water (wing-propelled diving), foraging in little auks is energetically expensive (Gabrielsen et al 1991;Konarzewski et al 1993;Stempniewicz 2001). As a consequence, they are forced to feed on energy-rich copepods associated with cold Arctic waters (Karnovsky et al 2003;Wojczulanis et al 2006;Jakubas et al 2007Jakubas et al , 2011a. Moreover, little auks use a dual foraging strategy consisting of several short and long trips (Steen et al 2007;Welcker et al 2009a;Wojczulanis-Jakubas et al 2010).…”