Earlier springs increase goose breeding propensity and nesting success at Arctic but not at temperate latitudes.

Intermittent breeding is an important tactic in long-lived species that trade off survival and reproduction to maximize lifetime reproductive success. When breeding conditions are unfavourable, individuals are expected to skip reproduction to ensure their own survival. Breeding propensity (i.e. the probability for a mature female to breed in a given year) is an essential parameter in determining reproductive output and population dynamics, but is not often studied in birds because it is difficult to obtain unbiased estimates. Breeding conditions are especially variable at high latitudes, potentially resulting in a large effect on breeding propensity of Arctic-breeding migratory birds, such as geese. With a novel approach, we used GPS-tracking data to determine nest locations, breeding propensity and nesting success of barnacle geese, and studied how these varied with breeding latitude and timing of arrival on the breeding grounds relative to local onset of spring. Onset of spring at the breeding grounds was a better predictor of breeding propensity and nesting success than relative timing of arrival. At Arctic latitudes (>66° N), breeding propensity decreased from 0.89 (95% CI: 0.65-0.97) in early springs to 0.22 (95% CI: 0.06-0.55) in late springs, while at temperate latitudes, it varied between 0.75 (95% CI: 0.38-0.93) and 0.89 (95% CI: 0.41-0.99) regardless of spring phenology. Nesting success followed a similar pattern and was lower in later springs at Arctic latitudes, but not at temperate latitudes. In early springs, a larger proportion of geese started breeding despite arriving late relative to the onset of spring, possibly because the early spring enabled them to use local resources to fuel egg laying and incubation. While earlier springs due to climate warming are considered to have mostly negative repercussions on reproductive success through phenological mismatches, our results suggest that these effects may partly be offset by higher breeding propensity and nesting success.

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.

Rapid formation of new migration route and breeding area by Arctic geese.

Many Arctic-breeding animals are at risk from local extirpation associated with habitat constriction and alterations in phenology in their Arctic environment as a result of rapid global warming.1 Migratory species face additional increasing anthropogenic pressures along their migratory routes such as habitat destruction, droughts, creation of barriers, and overexploitation.2,3 Such species can only persist if they adjust their migration, timing of breeding, and range.4 Here, we document both the abrupt (∼10 years) formation of a new migration route and a disjunct breeding population of the pink-footed goose (Anser brachyrhynchus) on Novaya Zemlya, Russia, almost 1,000 km away from the original breeding grounds in Svalbard. The population has grown to 3,000-4,000 birds, explained by intrinsic growth and continued immigration from the original route. The colonization was enabled by recent warming on Novaya Zemlya. We propose that social behavior of geese, resulting in cultural transmission of migration behavior among conspecifics as well as in mixed-species flocks, is key to this fast development and acts as a mechanism enabling ecological rescue in a rapidly changing world.