The foraging behaviour of little auks ( Alle alle ) in the Bjørndalen colony on the western coast of Spitsbergen was studied during the breeding season 2005. The duration of foraging trips and contents of gular pouches were analysed. Quantitative zooplankton samples procured in the vicinity of the colony facilitated a comparison between gular pouch contents and the availability of prey species. Zooplankton and gular pouch samples were all sampled within a time window of approximately one week. Using the Bray-Curtis similarity index, we determined that little auks in this colony have a bimodal foraging strategy consisting of long and short foraging trips with two corresponding distinct diets. Short trips are most likely to be centred on areas within the Isfjorden complex, whereas the birds are most likely to use the long trips (of typically more than 10 hours) to reach areas off the continental slope where they are able to feed selectively on large, energy-rich food items such as Calanus hyperboreus . This bimodal foraging strategy may be a response to the low availability of nutrientrich food close to the colony, which is insufficient to sustain both parents and chicks. Bimodal foraging trip strategies are well documented in many species in the Southern Ocean. This is the first study to show a similar feeding pattern in an Alcidae species in the Northern Hemisphere.
The foraging behaviour of little auks ( Alle alle ) in the Bjørndalen colony on the western coast of Spitsbergen was studied during the breeding season 2005. The duration of foraging trips and contents of gular pouches were analysed. Quantitative zooplankton samples procured in the vicinity of the colony facilitated a comparison between gular pouch contents and the availability of prey species. Zooplankton and gular pouch samples were all sampled within a time window of approximately one week. Using the Bray-Curtis similarity index, we determined that little auks in this colony have a bimodal foraging strategy consisting of long and short foraging trips with two corresponding distinct diets. Short trips are most likely to be centred on areas within the Isfjorden complex, whereas the birds are most likely to use the long trips (of typically more than 10 hours) to reach areas off the continental slope where they are able to feed selectively on large, energy-rich food items such as Calanus hyperboreus . This bimodal foraging strategy may be a response to the low availability of nutrientrich food close to the colony, which is insufficient to sustain both parents and chicks. Bimodal foraging trip strategies are well documented in many species in the Southern Ocean. This is the first study to show a similar feeding pattern in an Alcidae species in the Northern Hemisphere.
Unmanned aerial vehicles (UAVs) are increasingly being recognized as potentially useful for detection of marine mammals in their natural habitats, but an important consideration is the associated uncertainties in animal detection. We present a study based on field trials using UAVs to carry out image‐based monitoring of cetaceans in two fjords in northern Norway. We conducted 12 missions to assess the effects of both environmental‐ and aircraft‐related variables on detection certainty. Images were inspected for animal presence and its associated detection certainty. Images were also assessed for potentially important covariates such as wave turbulence (sea state), luminance, and glare. Aircraft variables such as altitude, pitch, and roll were combined into a single variable—pixel size. We recorded a total of 50 humpback whales, 63 killer whales (KW), and 118 unidentified sightings. We also recorded 57 harbor porpoise sightings. None of the environmental conditions (sea state, glare, and luminance) affected the detection certainty of harbor porpoises. In contrast, increasing sea state and luminance had negative and positive effects, respectively, on the detection certainty of humpback and KW. The detection certainty was not significantly affected by pixel size for both harbor porpoises, and humpback and KW. Our results indicate that at lower altitudes, variations in aircraft position (pitch and roll) do not have a variable effect on detection certainty. Overall, this study shows the importance of measuring variability in both environmental and flight‐related variables, in order to attain unbiased estimates of detectability for UAV‐based marine mammal surveys, particularly in Arctic and sub‐Arctic regions.
In species that aggregate for reproduction, the social and fitness costs of movement between groups frequently lead to restricted exchange between breeding areas. We report on four individual humpback whales identified in both the Cape Verde Islands and Guadeloupe; locations separated by an ocean basin and >4000 km. This rate of exchange is rarely encountered between such geographically discrete breeding areas. Two individuals returned to the area where they were originally identified. In contrast, no individuals from the Cape Verde Islands were resighted to the much larger sample from the Dominican Republic, though the migratory distances from the feeding areas are comparable between these areas. The social factors driving the stark difference between groups that is observed here are not clear. Effective conservation requires an understanding of the extent and pattern of movement between population units. The findings presented here suggest that there may well be more than one behaviourally distinct group within the West Indies. More broadly, they argue that considerable caution is warranted in assumptions made regarding the number, boundaries and status of population units based solely on spatial separation or proximity.
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