Breeding phenology and postnatal development data of northern bats (Eptesicus nilssonii)

Bats inhabiting northern latitudes are faced with short reproductive seasons during which they must produce and rear pups before fattening up in time to survive the winter hibernation. Therefore, the timing of parturition has considerable impacts on future fitness prospects for mother and pup. However, little is known about individual variation in breeding phenology and its consequences for postnatal development within bat populations. Here, we studied the phenology of breeding in Eptesicus nilssonii across seven years using data collected by day-to-day monitoring of a breeding colony in Norway (60.1°N) for which the identity and age of each mother (N = 8) and pup (N = 28) were known. Using mixed-effect models, we found that arrival at the colony was influenced by temperature conditions from mid-April to mid-May across all females, but that there were strong and consistent individual differences in arrival- and parturition time across years. Females generally arrived ~32.1 days before giving birth but the gestation duration was reduced if females arrived late, and prolonged if females left the colony when faced with cold weather conditions. Pups born later in the season were born smaller but had higher growth rates during the most rapid growth period (<10 days old). The within-individual effects suggest that the higher growth rates could be due to mothers compensating (e.g. through increased food intake) for late parturition rather than by improved food availability. Date of parturition did not influence adult body size in pups. Pups became volant at the earliest only 13.1 days after birth and approached adult flight patterns during their first flight week. Our results suggest that E. nilssonii is highly adapted to a short breeding season by producing large, fast developing and early volant pups, despite the environmental pressures bats face at northern latitudes.

栖息于高纬度北部地区的蝙蝠，繁殖季极为短促——它们必须在此期间完成幼崽的产下与抚育，随后及时积累脂肪以顺利度过冬季冬眠。因此，产仔时机对母蝠与幼崽的未来生存适合度具有显著影响。然而，目前学界对蝙蝠种群内部繁殖物候的个体差异及其对产后发育的影响仍缺乏深入认知。本研究以挪威北纬60.1°处的一处蝙蝠繁殖群为研究对象，通过连续七年的日常监测获取数据，对北棕蝠（Eptesicus nilssonii）的繁殖物候展开研究；该种群中每头母蝠（样本量N=8）与幼崽（N=28）的身份及年龄均已明确。通过混合效应模型（mixed-effect models）分析，我们发现：所有雌性个体抵达繁殖群的时间，均受4月中旬至5月中旬的气温条件调控；但不同年份中，雌性的抵达时间与产仔时间均存在显著且稳定的个体差异。通常情况下，雌性个体在分娩前约32.1天抵达繁殖群；若雌性抵达过晚，则妊娠期会缩短，而若雌性因遭遇寒冷天气而离开繁殖群，则妊娠期会相应延长。繁殖季后期出生的幼崽初生体型更小，但在出生后的最快生长阶段（<10日龄）拥有更高的生长速率。个体内效应分析结果显示，较高的生长速率或源于母蝠对晚产的补偿行为（例如通过增加食物摄入量），而非食物可获得性的提升。产仔日期并未对幼崽的成年体型产生显著影响。幼崽最早仅在出生后13.1天即可实现飞行，并在首次飞行的一周内逐渐趋近于成体的飞行模式。本研究结果表明，尽管高纬度北部地区的蝙蝠面临诸多环境压力，但北棕蝠通过产下体型较大、发育较快且较早具备飞行能力的幼崽，高度适应了短促的繁殖季。