Nocturnal foraging lifts time-constraints in winter for migratory geese but hardly speeds up fueling

Climate warming advances the optimal timing of breeding for many animals. For migrants to start breeding earlier, a concurrent advancement of migration is required, including premigratory fueling of energy reserves. We investigate whether barnacle geese are time constrained during premigratory fueling and whether there is potential to advance or shorten the fueling period to allow an earlier migratory departure. We equipped barnacle geese with GPS trackers and accelerometers to remotely record birds’ behavior, from which we calculated time budgets. We examined how time spent foraging was affected by the available time (during daylight and moonlit nights) and thermoregulation costs. We used an energetic model to assess onset and rates of fueling and whether geese can further advance fueling by extending foraging time. We show that, during winter, when facing higher thermoregulation costs, geese consistently foraged at night, especially during moonlit nights, in order to balance their energy budgets. In spring, birds made use of the increasing day length and gained body stores by foraging longer during the day, but birds stopped foraging extensively during the night. Our model indicates that, by continuing nighttime foraging throughout spring, geese may have some leeway to advance and increase fueling rate, potentially reaching departure body mass 4 days earlier. In light of rapid climatic changes on the breeding grounds, whether this advancement can be realized and whether it will be sufficient to prevent phenological mismatches remains to be determined

Year-round activity levels reveal diurnal foraging constraints in the annual cycle of migratory and non-migratory barnacle geese

Performing migratory journeys comes with energetic costs, which have to be compensated within the annual cycle. An assessment of how and when such compensation occurs is ideally done by comparing full annual cycles of migratory and non-migratory individuals of the same species, which is rarely achieved. We studied free-living migratory and resident barnacle geese belonging to the same flyway (metapopulation), and investigated when differences in foraging activity occur, and when foraging extends beyond available daylight, indicating a diurnal foraging constraint in these usually diurnal animals. We compared foraging activity of migratory (N = 94) and resident (N = 30) geese throughout the annual cycle using GPS-transmitters and 3D-accelerometers, and corroborated this with data on seasonal variation in body condition. Migratory geese were more active than residents during most of the year, amounting to a difference of over 370 h over an entire annual cycle. Activity differences were largest during the periods that comprised preparation for spring and autumn migration. Lengthening days during spring facilitated increased activity, which coincided with an increase in body condition. Both migratory and resident geese were active at night during winter, but migratory geese were also active at night before autumn migration, resulting in a period of night-time activity that was 6 weeks longer than in resident geese. Our results indicate that, at least in geese, seasonal migration requires longer daily activity not only during migration but throughout most of the annual cycle, with migrants being more frequently forced to extend foraging activity into the night

Outflying climate change: Optimal timing of migratory geese breeding in a warming Arctic

Climate change is occurring at different rates along the flyways of migratory birds, with the most rapid climate warming in the Arctic. Migratory birds breeding here may be unable to advance migration timing to match this shift in environmental conditions, as they are (1) constrained in time to prepare for an earlier migration, or (2) as their wintering grounds do not provide cues that correctly predict the optimal timing of migration. The central aim of this thesis is to uncover the most important limiting factor for advancing timing of migration and reproduction for an Arctic migratory bird, the barnacle goose. By combining model predictions, data from long-term field studies and data from modern tracking-devices, it is shown that geese are initially not time-constrained to advance fuelling for migration. However, they seem to miss cues to adjust their migration departure from temperate wintering and stopover sites to changing conditions in the Arctic. Once in the Arctic, geese can advance arrival in early springs by accelerating migration speed. Nevertheless, they become time-constrained to adequately adjust reproduction timing, as they first need to refuel on the breeding grounds after a fast migration before they are able to breed. A phenological mismatch arises when geese breed too late in relation to the local peak in food quality, and their chicks suffer from reduced survival. While geese show some flexibility to adjust migration timing in the Arctic, successful adaptation to a warming Arctic may hinge on their ability to adjust migration timing in temperate regions