Data from: Timing of arrival in the breeding area is repeatable and affects reproductive success in a non-migratory population of blue tits

Events in one part of the annual cycle often affect the performance (and
subsequently fitness) of individuals later in the season (carry-over
effects). An important aspect of this relates to the timing of activities.
For example, many studies on migratory birds have shown that relatively
late spring arrival in the breeding area reduces both the likelihood of
getting a mate or territory and reproductive success. In contrast,
relatively little is known about movements of individuals in non-migratory
populations during the non-breeding season. Few studies have investigated
the timing of arrival at the breeding area in such species, possibly due
to the assumption that most individuals remain in the area during the
non-breeding season. In this study, we used four years of data from a
transponder-based automated recording system set up in a non-migratory
population of blue tits (Cyanistes caeruleus) to describe individual
variation in arrival at the breeding site. We investigated whether this
variation can be explained by individual characteristics (sex, body size,
or status), and we assessed its effect on aspects of reproductive success
in the subsequent breeding season. We found substantial variation in
arrival date and demonstrate that this trait is individual-specific
(repeatable). Females arrived later than males, but the arrival dates of
social pair members were more similar than expected by chance, which
suggests that individuals may mate assortatively depending on their
arrival in the breeding area. Arrival predicted both whether an individual
would end up breeding that season, and several aspects of its breeding
success. Our study suggests that individuals of non-migratory species
leave the breeding area during the non-breeding season. Hence, it may be
useful to consider variation in the scale of movements between breeding
and non-breeding sites, rather than using a simple dichotomy between
“resident” and “migratory” species. We conclude that the timing of
pre-breeding events, in particular arrival date, may be an overlooked, but
important, fitness-relevant trait in non-migratory species.

年度周期中某一阶段的事件，往往会影响个体当季后期的表现及后续的适合度（fitness），即延续效应（carry-over effects）。其中一个关键方面与活动时序密切相关。例如，诸多针对候鸟的研究表明，春季抵达繁殖地的时间越晚，个体获得配偶或领地的概率，以及繁殖成功率均会随之降低。与之相对，学界对非迁徙种群个体在非繁殖季的移动模式却知之甚少。鲜有研究探讨此类物种抵达繁殖地的时序，这可能源于学界此前的普遍假设：多数个体在非繁殖季会留守繁殖地。

本研究依托一套基于应答器（transponder）的自动记录系统，该系统布设於一个非迁徙性蓝山雀（Cyanistes caeruleus）种群中，我们利用其四年的观测数据，刻画了个体抵达繁殖地的时序变异规律。本研究探究了该时序变异是否可通过个体特征（性别、体型或社会地位）加以解释，并评估了其对后续繁殖季繁殖成功率若干维度的影响。

研究结果显示，个体抵达日期存在显著变异，且该性状具有个体特异性（即可重复性）。雌性个体的抵达时间晚于雄性，而配对配偶间的抵达日期相似度显著高于随机预期，这表明个体可能会根据抵达繁殖地的时序进行选型交配。抵达时序不仅能够预测个体当季是否能够成功繁殖，还能解释其繁殖成功率的多个维度。

本研究表明，非迁徙物种种群的个体在非繁殖季会离开繁殖地。因此，相较于简单地将物种划分为"resident"（留居）与"migratory"（迁徙）两类，考虑繁殖地与非繁殖地间移动规模的变异或许更具研究价值。

综上，我们认为在非迁徙物种种群中，繁殖前活动的时序（尤其是抵达日期）或许是一个长期被忽视但却至关重要的、与适合度相关的性状。