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

Abstract

During the chick-rearing period, little auks Alle alle adopt a bimodal foraging strategy, alternating long trips with several short ones. It has been postulated that they reach more remote areas during long feeding trips than during short ones. However, the range of their foraging Xights has never actually been measured. The aims of this study were to Wnd the exact location of the little auk feeding grounds and to investigate whether they reach remote areas during long foraging trips using miniature GPS and temperature loggers. The study was conducted in 2009 in Magdalenefjorden (79°34ЈN, 11°04ЈE), one of the main breeding grounds of little auks on Spitsbergen. The temperature logger records indicated that during short trips, little auks visit warmer waters (situated close to the colony) than during long ones. The tracks of two GPS-equipped birds indicated that during long trips little auks foraged in the distant, foodabundant marginal sea ice zone, at least 100 km away from the colony. During long trips, birds make several stops at sea, perhaps sampling the foraging area with respect to prey distribution. Since food conditions near the studied colony are usually suboptimal, little auks may be exploiting distant feeding areas to compensate for the poorer-quality food available at nearby foraging grounds. The extended duration of long foraging trips may enable birds to collect food for chicks on food-abundant, remote foraging grounds as well as acquire, process and excrete food needed for selfmaintenance, reducing the costs of Xight to the colony.

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

“…Despite the fact that loggers did not restrain parent birds from reaching remote foraging areas (Jakubas et al 2011b), some aspects of their behaviour, feeding frequency, and consequently, chick growth were impaired.…”

“…Temperature and GPS records from the same experimental birds were used to study their foraging ecology and published separately (Jakubas et al 2011b). In the current paper, we focus on the influence of both types of loggers carried by parent birds on chick growth and development, while changes in foraging performance of parent birds were investigated only in birds loaded with temperature loggers.…”

“…On the basis of the recorded temperature distribution, three main types of little auk activity were distinguished: presence in the colony, flight and presence on the water (Tremblay et al 2003;Welcker et al 2009a;Jakubas et al 2011b). The period of high temperatures was considered to be a presence in the colony.…”

“…A further steep decrease in temperature was considered as landing on the water and presence on the sea surface. Subsequent rapid increase in temperature was interpreted as take-off from the water and flight (see Jakubas et al 2011b for more details). The frequency distribution of foraging trip durations was bimodal, shown as two separate log-normal distributions of short and long trips (see later).…”

“…The ranges of short trips were calculated to 12-33 km and long trips to 130-219 km, based on the mean flight times of parent birds equipped with time-depth recorders (Welcker et al 2009a). Data from GPS loggers confirm that little auks are able to forage on distant feeding grounds ([100 km away from the colony) (Jakubas et al 2011b).…”