Data from: 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 pre-migratory fueling of energy reserves.
We investigate whether barnacle geese are time-constrained during
pre-migratory 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
night-time 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.

气候变暖使得多数动物的最佳繁殖时段提前。对于迁徙物种而言，若要更早启动繁殖，需同步推进迁徙进程，其中涵盖迁徙前的能量储备积累。本研究旨在探究藤壶雁（barnacle goose）在迁徙前能量储备阶段是否受时间约束，以及是否存在提前或缩短储备周期以实现更早启程迁徙的可能性。我们为藤壶雁佩戴GPS追踪器与加速度计，以远程记录其行为活动，并据此计算其行为时间分配（time budgets）。我们分析了觅食时长如何受到可利用时间（包括白昼与月夜时段）以及体温调节成本（thermoregulation costs）的影响。我们采用能量模型（energetic model）评估储备启动时机与积累速率，并探究雁群能否通过延长觅食时长进一步提前能量储备进程。研究结果显示，冬季时因体温调节成本升高，藤壶雁会持续在夜间觅食，尤其偏好月夜时段，以此维持自身能量收支平衡。春季时，藤壶雁利用白昼时长渐增的有利条件，通过延长日间觅食时长积累体脂储备，但夜间觅食活动大幅减少。我们的模型表明，若在整个春季持续开展夜间觅食，藤壶雁或可获得提前储备并提升积累速率的空间，有望提前4天达到迁徙启程所需的体质量。鉴于繁殖地正经历快速气候变化，该提前策略能否得以实施，以及是否足以避免物候错配（phenological mismatches）现象，仍有待进一步探明。