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 bar-
nacle 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.
- Annual cycle
- Day length