Flexibility of little auks foraging in various oceanographic features in a changing Arctic

Abstract

Using GpS-tracked individuals, we compared foraging ecology and reproductive output of a High-Arctic zooplanktivorous seabird, the little auk Alle alle, between three years differing in environmental conditions (sea surface temperature). Despite contrasting environmental conditions, average foraging fights distance and duration were generally similar in all studied years. Also, in all years foraging locations visited by the little auk parents during short trips (St, for chick provisioning) were significantly closer to the colony compared to those visited during long trips (LTs, mainly for adults' self-maintenance). Nevertheless, we also found some differences in the little auk foraging behaviour: duration of Lts was the longest in the coldest year suggesting more time for resting for adults compared to warmer years. Besides, birds foraged closer to the colony and in significantly colder water in the coldest year. Interestingly, these differences did not affect chick diet: in all the years, the energy content of food loads was similar, with the Arctic copepod, Calanus glacialis copepodite stage V being the most preferred prey item (>73% of items by number and >67% by energy content). Also chick survival was similar in all the study years. However, when examining chicks growth rate we found that their peak body mass was lower in warmer years suggesting that overall conditions in the two warm years were less favourable. While our results, demonstrate a great foraging flexibility by little auks, they also point out their vulnerability to changing environmental conditions. Optimal foraging theory predicts that animals should adjust their foraging behaviour to environmental condition the way to maximise net energy gain and to increase their survival and/or reproductive success 1. The ability to efficiently adjust foraging behaviour should be especially apparent in central place foragers, such as seabirds that forage at distant locations from which they need to regularly return to the colony to feed their young 2. Prey distribution and abundance vary spatially and temporally in response to macroscale fluctuations of oceanographic conditions (e.g., North Atlantic Oscillation, El Niño Southern Oscillation; 3,4 as well as to mesoscale processes [e.g., sea ice dynamics, sea current distribution, upwelling strength and spread, atmospheric blocking; e.g. 5-9 ]. Seabirds are generally well adapted to the foraging in such the heterogeneous marine habitat. However, the recent climate change increases additional, often unpredictable fluctuations in prey abundance 10,11. It is specially visible in the Arctic where both marine and terrestrial ecosystems are rapidly changing as climate warming affects these regions faster than the global average 12-15. Moreover, high-latitude nesting seabirds have a limited time window to reproduce, which may limit their ability to adjust the timing of breeding to shifts in peaks of food abundance 7. Thus, Arctic endemic species are extremely susceptible to climate change. In the high Arctic marine ...

Duration of female parental care and their survival in the little auk Alle alle - are these two traits linked?

“…chicks age at fledging) in Hornsund and Magdalenefjorden colony (left panel), and bootstrap distribution of the inter-colony difference in mean day of the chicks fledging (right panel); the black vertical line at 0, being within the range of the permutated distribution, indicates no significant difference between the two colonies in the duration of the nesting period as long as it is necessary. Adjustment of parental behaviour by female little auks to current environmental conditions is consistent with the great flexibility of the species observed in various contexts related to foraging (Jakubas et al 2011(Jakubas et al , 2016(Jakubas et al , 2020Brown et al 2012;Gremillet et al 2012;Amélineau et al 2016).…”

In a comfort zone and beyond—Ecological plasticity of key marine mediators

“…This could be especially the case for C. finmarchicus , whose demography was very similar between the fjord and shelf and which is probably mostly advected to the fjord. The small‐scale difference between fjord and shelf populations in demographic structure of C. glacialis, especially regarding the relative proportions between younger life stages and the most lipid‐rich fifth stage (CV), could be of great importance for CV‐selective predators such as little auks (Balazy et al., 2019; Jakubas et al., 2020; Welcker et al., 2009) and may explain why birds tend to forage on the shelf rather than in the fjord in the time window of their main feeding requirements (Jakubas et al., 2013).…”

“…Due to the commonly observed difference in the size and thus the amount of lipids between C. finmarchicus and C. glacialis , the two species were believed to support different arctic food webs (Renaud et al., 2018; Weslawski et al., 2009). The decreased availability of C. glacialis is expected to affect the breeding success of the most numerous seabirds, little auks (Jakubas et al., 2020; Stempniewicz et al., 2007). However, the predicted higher abundance of C. finmarchicus in the Arctic (Reygondeau & Beaugrand, 2011; Slagstad et al., 2011) is expected to favor fish stocks (Falk‐Petersen et al., 2007; Renaud et al., 2018; Stempniewicz et al., 2007).…”

The Little Auk Alle alle: an ecological indicator of a changing Arctic and a model organism

“…The impact of the latter group on terrestrial ecosystems is therefore much smaller compared to Little Auks because the guano deposited on the seabird cliffs is rapidly washed out to sea (Stempniewicz et al 2007). These results clearly indicate that the Little Auk Preference and specialization on a superior prey type that guarantees the best net energy gain (Weslawski et al 1999;Karnovsky et al 2003;Vogedes et al 2014;Møller et al 2018) Flexibility of foraging behaviour Spatio-temporal variation in environmental conditions in foraging areas (Jakubas et al , 2016(Jakubas et al , 2017(Jakubas et al , 2020Welcker et al 2009a, b;Harding et al 2009a;Kwasniewski et al 2010Kwasniewski et al , 2012Karnovsky et al 2011;Brown et al 2012;Grémillet et al 2012;Amélineau et al 2019) Predator-prey interaction Highly synchronized breeding, strong interrelationships with a limited number of predators (Stempniewicz 1995;Burnham 2005;Wojczulanis et al 2005;Jakubas and Wojczulanis-Jakubas 2010) Trade-off between the benefits of investment in current offspring and costs to future reproduction Long-lived, iteroparous species with low annual fecundity are less exposed to the risk of mortality during a given breeding attempt (Gębczyński et al 1996;…”

“…Even where and when the preferred Arctic zooplankton is less abundant, they have been able to breed successfully with no negative consequences on chick survival, stress levels, or the body masses of adults and chicks (Kwasniewski et al 2010;Jakubas et al , 2017Grémillet et al 2012). However, some studies have reported serious consequences of suboptimal foraging conditions-a slower chick growth rate (Jakubas et al , 2020Kidawa et al 2015), a decrease in interannual survival rates of adult Little Auks (Hovinen et al 2014a) with a potentially strong effect on population dynamics and viability in such a long-lived species (Saether and Bakke 2000). It has been found that interannual changes in sea ice phenology and primary productivity pulses (affecting the transfer of biomass and energy through Arctic food webs) in Svalbard affected the breeding performance of Little Auks: chick survival decreased with the increasing time lag between the annual peaks of sea ice extent and primary production (Ramírez et al 2017).…”