Data from: Biparental incubation patterns in a high-Arctic breeding shorebird: how do pairs divide their duties?

In biparental species, parents may be in conflict over how much they invest into their offspring. To understand this conflict, parental care needs to be accurately measured, something rarely done. Here, we quantitatively describe the outcome of parental conflict in terms of quality, amount and timing of incubation throughout the 21 day incubation period in a population of semipalmated sandpipers (Calidris pusilla) breeding under continuous daylight in the High Arctic. Incubation quality, measured by egg temperature and incubation constancy, showed no marked difference between the sexes. The amount of incubation, measured as length of incubation bouts, was on average 51 min longer per bout for females (11.5 h) than for males (10.7 h), at first glance suggesting that females invested more than males. However, this difference may have been offset by sex-differences in the timing of incubation; females were more often off-nest during the warmer period of the day, when foraging conditions were presumably better. Overall, the daily timing of incubation shifted over the incubation period (e. g., for female incubation from ‘evening-night’ to ‘night-morning’) and over the season, but varied considerably among pairs. At one extreme, pairs shared the amount of incubation equally, but one parent always incubated during the colder part of the day; at the other extreme, pairs shifted the start of incubation bouts between days so that each parent experienced similar conditions across the incubation period. Our results highlight how the simultaneous consideration of different aspects of care across time allows sex-specific investment to be more accurately quantified.

在双亲育幼物种（biparental species）中，父母双方可能会在对后代的育幼投入比例上产生冲突。为解析这类育幼冲突，需对双亲育幼行为开展精准量化测定，而此类系统性测定目前仍较为匮乏。本研究以高北极（High Arctic）地区持续光照环境下繁殖的半蹼滨鹬（Calidris pusilla）种群为研究对象，针对其21天的完整孵卵周期，从孵卵质量、孵卵总量与孵卵时序三个维度，定量刻画了双亲育幼冲突的具体表现。以卵温与孵卵持续性（incubation constancy）为测定指标的孵卵质量，在雌雄双亲间未呈现显著差异。以孵卵回合（incubation bouts）时长为指标测算的单次孵卵总时长，雌性个体每回合平均时长（11.5小时）较雄性（10.7小时）多出51分钟，乍看之下似乎雌性的育幼投入更高。但该差异可能因雌雄双亲在孵卵时序上的另一组差异被抵消：雌性往往在当日温度较高、觅食条件大概率更佳的时段离巢（off-nest）。整体而言，孵卵的每日时序会随孵卵周期（例如雌性的孵卵时段从“傍晚-夜间”转变为“夜间-清晨”）与繁殖季发生动态推移，但不同繁殖对间的孵卵时序差异显著。存在两类极端的孵卵分工模式：一类是繁殖对双方的孵卵时长完全均等，但其中一方始终在当日温度较低的时段承担孵卵任务；另一类则是繁殖对会在不同日期调整孵卵回合的起始时间，使双亲在整个孵卵周期中均能经历相近的环境条件。本研究结果表明，若能综合考量育幼行为在时间维度上的多维度特征，便可更为精准地量化雌雄双亲各自的育幼投入水平。