Study area with the locations of the little auk Alle alle colonies in Magdalenefjord (upper asterisk) and Hornsund (lower asterisk) within a 50 km radius from each site (black circles). The map was prepared using Ocean Data View software (Schlitzer 2011). 

Contexts in source publication

Context 1

... one of the highest mass-specific daily energy expenditures among seabirds (Gabrielsen et al. 1991). Owing to its small wing area and subsequent high wing loading, both in the air (flapping flight) and in the water (wing-propelled diving; Stempniewicz 1982; Gabrielsen et al. 1991), foraging is energetically expensive. Also, the energy demands of the chick are much higher than those of other seabird chicks of similar body size (Konarzewski et al. 1993). High energy demands force little auks to focus on energy- rich calanoid copepods that are associated with cold Arctic waters, such as Calanus glacialis Jaschnov, 1955 (Falk-Petersen et al. 1990, 2009; Karnovsky et al. 2003, 2010; Wojczulanis et al. 2006; Jakubas et al. 2007, 2011). Studies in west Spitsbergen have shown that little auks fed their chicks mainly with large C. glacialis (copepodid stage CV), while smaller and less energetically profitable Calanus finmarchicus (Gunnerus, 1770) and younger life stages of C. glacialis were avoided, even if they were equally or more abundant in the foraging grounds (Karnovsky et al. 2003; Jakubas et al. 2007, 2011; Kwa ś niewski et al. 2010, 2012; Vogedes et al. 2014). The composition of zooplankton communities is closely linked to oceanographic conditions (i.e. the distribution of Atlantic and Arctic water masses), with species of different size and energetic value adapted to the characteristics of different water masses (Scott et al. 2000; Beaugrand et al. 2002; Falk-Petersen et al. 2007; B ł achowiak-Samo ł yk et al. 2008). The proportion of C. glacialis CV in relation to other zooplankters may reflect the quality of foraging conditions for planktivorous seabirds (Kwa ś niewski et al. 2010; Stempniewicz et al. 2013). During the chick-rearing period little auk parents adopt a dual foraging strategy, alternating long trips with several consecutive short trips (Steen at al. 2007; Welcker et al. 2009a; Wojczulanis-Jakubas et al. 2010). Long foraging trips are primarily devoted to self-feeding, while the short ones are performed to maximize chick-feeding rates (Jakubas et al. 2012; Welcker et al. 2012). The flexibility of foraging trip duration and chick-feeding frequency may serve as an important mechanism enabling little auks to adjust their foraging strategy and breeding effort to fluctuations in food availability. Previous studies demonstrated that with increasing water mass temperature, the overall time spent foraging by little auks tended to increase (Jakubas et al. 2007, 2011; Welcker et al. 2009a; Kwa ś niewski et al. 2010; Grémillet et al. 2012). For all these reasons, the little auk constitutes a particularly interesting species to test hypotheses about the relationship between environmental conditions, foraging behaviour and breeding success. However, a comprehensive study linking a number of variables characterizing foraging ground quality, measured directly at sea, with the birds ’ foraging strategy, parental efforts, body condition and nestling survival is lacking. We hypothesized that under poor foraging conditions, i.e. high water temperature and low proportion of the preferred C. glacialis to C. finmarchicus in the foraging grounds, little auk parents would prior- itize their own energetic demands. We expect that they would change their foraging strategy by increasing the overall duration of foraging trips, decreasing the frequency of short foraging trips (in relation to long foraging trips), and consequently decreasing the frequency of chick feeding. Accordingly, the growth and survival of their chicks might be impaired, while the body mass of adult birds might remain unaf- fected. To verify these predictions, we investigated the response of little auks to the foraging conditions that varied on an inter-annual and inter-colony basis, which constituted a natural experiment for the presented hypothesis. The study was carried out in an area with large breeding aggregations of little auks on Spitsbergen (Isaksen 1995), on the Magdalenefjord (Høystakken and Alkekongen mountain slopes; 79°35 ′ N, 11°05 ′ E) and Hornsund Fjord (Ariekammen mountain slope; 77°00 ′ N, 15°33 ′ E; Figure 1). The oceanographic data were collected on the west Spitsbergen shelf at ...

Context 2

... within a 50 km radius from each colony ( Figure 1). The sampling area corresponded well to the little auks ’ core foraging area at sea, determined from at-sea direct observations (Karnovsky et al. 2003, 2010; Stempniewicz et al. 2013) and the actual foraging position of GPS-equipped individuals (Jakubas et al. 2013). Data concerning the foraging grounds, food delivered to chicks, parental efforts and adult body mass were collected between 24 July and 4 August, in 2009 and 2010. The sampling period corresponded to the mid-chick-rearing period (chicks at age 10 – 18 days, determined by median hatching dates in each colony and season). To obtain the median date of hatching, chick body mass and survival, little auks ’ nests were monitored from late incubation and continuing to the fledging period (i.e. between 10 July and 10 August in 2009 and 2010). The two study areas are characterized by different hydrographical regimes. The Hornsund area is influ- enced largely by the coastal Sørkapp Current carrying cold, less-saline Arctic-type waters from the northeast Barents Sea in addition to the West Spitsbergen Current, which transports warm saline Atlantic waters from the Norwegian Sea (Piechura et al. 2001; Cottier et al. 2005). In the Magdalenefjord area, the West Spitsbergen Current predominates on the shelf slope (Saloranta & Svendsen 2001). Additionally, a marginal sea ice zone is situated relatively close (about 100 km north) to the Magdalenefjord colony (Jakubas et al. 2012, 2013). Measurements and sampling at sea were carried out by the research vessel ‘ Oceania ’ (Institute of Oceanology, Polish Academy of Sciences). Temperature and salinity in the foraging grounds of the little auks were measured with a FastCat CTD (Sea-Bird Electronics) producing profiles of the upper 50 m of the water column and the averaged values for the layer were analysed. To sample zooplankton, a WP-2 net with a 0.25 m 2 opening fitted with 500 μm mesh was used. The net was hauled vertically from a depth of 50 m to the surface and the zooplankton sample was preserved in 4% formaldehyde – seawater solution, buffered with borax. Sampling was conducted at 10 and 11 stations in Hornsund (in 2009 and 2010, respectively) and at 15 stations in Magdalenefjord in each season. To collect the chick diet samples, adult birds were randomly captured in the colony using a mist-net or noose-carpets. Only birds with the gular pouch full of food were considered. The content of the pouch was gently scooped out with a small plastic spoon. Each food load was put in a separate plastic box and preserved in 4% formaldehyde seawater solution. In total, 30 food samples were collected from each colony and season. In order to record the chick feeding frequency and the duration of foraging trips, 25 and 33 birds in Hornsund and 42 and 41 birds in Magdalenefjord in 2009 and 2010, respectively, were captured in their nests or in the colony using a mist-net or noose- carpets and marked (individual combinations of colour rings and colour dye on the birds ’ breasts). Two 24 hour continuous observations of all marked birds were performed in each colony and season (except for Hornsund in 2009, where only one obser- vation was performed). The observed birds nested in close proximity, allowing two observers to follow all birds. The presence of the birds was monitored continuously and all departures and arrivals with/ without food of the marked individuals were recorded. All adult birds caught in the colony (in total, 71 and 124 birds in Hornsund and 145 and 101 in Magdalenefjord in 2009 and 2010, respectively) were weighed using a PESOLA® balance (± 1.0 g) and measured (head – bill length) using callipers (± 0.1 mm). Small blood samples (20 μl) for DNA-based sex identification were collected from the brachial vein (following the procedure described in Owen 2011). Each sample was stored in 1 ml of 96% ethanol. Birds were released after about 10 min of careful handling without any harm. To study chick survival, 81 and 137 little auk nests were monitored in Hornsund and 157 and 152 in Magdalenefjord in 2009 and 2010, respectively. Every 2 – 3 days, the nests were checked for nestling presence/absence. Additionally, 33 and 18 chicks in Hornsund and 17 and 19 chicks in Magdalenefjord in 2009 and 2010, respectively, were weighed every 3 days from the age of 14 15 days until fledging. All zooplankton samples collected at sea and chick diet samples were examined following the procedures described in Kwa ś niewski et al. (2010). Calanus spp. were identified to species and developmental stage (copepodid) based on the description given in Kwa ś niewski et al. (2003). Other zooplankton was identified to the lowest possible taxonomic level, and the body length of each individual was measured for the purpose of biomass calculations. DNA for sexing was extracted from coagulated blood (after ethanol evaporation) using a Blood Mini Kit (A&A Biotechnology, Gdynia, Poland). CHD-gene based analyses were performed with the primer pair F2550 and R2718 according to Griffiths et al. (1998) using a 50°C annealing temperature for the polymerase chain reaction (PCR). The ...