Data for: Shy-boldness cannot predict egg rejection in the Japanese tit

During the breeding season (April-June) of year 2022, when Japanese tits were found occupying nest boxes, breeding nests were regularly monitored to determine the dates of the first eggs. Female Japanese tits usually started incubation the day after laying their last egg (Zhang et al. 2020), and therefore, we defined the date when the females laid their last eggs as day 0 of the incubation period. After determining that the Japanese tits had entered the incubation period, we began an escape behavior test and a foreign egg recognition experiment among the female Japanese tits. In order to measure escape behavior, researchers slowly approached the nest box from about 10 m and gazed at the hole to record whether the females flew away, though the orientation of the approaching was adjusted according to location of focal nest boxes. If the female did not fly out from nest boxes when the experimenter went under the tree hung up nest box, we climbed the tree. We defined females that flew away from the nest box as shy individuals and those that did not as bold individuals during this process. If the females were not in the nest at the time of the first experiment, this experiment was repeated on the second day until escape behavior of the incubating females was recorded. After waiting for the departure of the females, we placed one foreign egg in the nest cup after clutch completion (i.e., on the first day when the host began to incubate) (Figure 1a), while recording the experiment date and the clutch size in the experimental nest. In this study, most egg experiments were conducted on the day when the clutch of tits were completed or the next day, and only a small number of nests could not be determined for their incubation time. However, none of the experimental nests hatched after 6 days of the egg recognition experiment (see below), suggesting that all of these nests should have been in the early to mid-incubation period (i.e., 10-15 days for Japanese tits) at the time of egg experiments. The foreign eggs used in the experiment were the commercial non-fertilized eggs of white-rumped munia (Lonchura striata), colored with a blue non-toxic and odorless marker, which were slightly smaller in size than the experimental tit species (see Liu et al. 2019 for the exact egg sizes of Japanese tits and white-rumped munias). We set the length of the egg rejection experiment to 6 days, and considered females of the experimental nest not to reject foreign eggs if the incoming eggs remained in the experimental nest and the nest was not abandoned within 6 days. Females of the experimental nest were considered to reject foreign eggs if within 6 days, the incoming eggs disappeared or remained in the nest box but the females did not incubate them (i.e., buried under the nest material or not in the nest cup, as shown in Figure 1b) (i.e., Yang et al. 2015; Liang et al. 2016; Liu et al. 2019). Some studies have suggested that nest abandonment is also one of the ways host birds reject foreign eggs (Hanley et al. 2016), but nest abandonment was not found in our experiments. If the experimental nest succumbed to predation within 6 days, experimental results from that nest were not counted.2022年繁殖季（4月至6月），当日本山雀（Japanese tits）占据巢箱后，研究人员对其繁殖巢开展定期监测，以确定首枚卵的产卵日期。雌性日本山雀通常在产下最后一枚卵的次日启动孵卵行为（Zhang等，2020），因此我们将雌性产下最后一枚卵的日期定义为孵卵期的第0天。在确认日本山雀进入孵卵期后，随即对雌性个体开展逃逸行为测试与外来卵识别实验。 为测定逃逸行为，研究人员从约10米外缓慢趋近巢箱，凝视巢洞以记录雌性是否飞离，趋近方向将根据目标巢箱的位置进行调整。若实验者行至悬挂巢箱的树下时，雌性仍未飞出巢箱，则研究人员将爬树完成后续观察。本测试中，我们将从巢箱飞离的雌性个体定义为羞怯型个体，未飞离的定义为大胆型个体。若首次测试时雌性不在巢中，则于次日重复实验，直至记录到孵卵雌性的逃逸行为。 待雌性离巢后，我们在产卵终了（即宿主开始孵卵的首日）向巢杯内放置一枚外来卵（图1a），同时记录实验日期与实验巢的窝卵数。本研究中，多数卵实验于山雀产卵完成当日或次日开展，仅少量巢无法确定其孵卵起始时间。但所有实验巢均未在外来卵识别实验启动后的6天内出现雏鸟孵化，这表明实验开展时所有巢均处于孵卵早期至中期（日本山雀的孵卵期为10至15天）。 实验所用外来卵为商用非受精白腰文鸟（Lonchura striata）卵，经蓝色无毒无臭记号笔染色处理，其尺寸略小于实验所用山雀物种（日本山雀与白腰文鸟的精确卵尺寸详见Liu等，2019）。我们将卵拒斥实验的时长设置为6天：若6天内外来卵仍留存于实验巢中且巢未被弃用，则认定该巢雌性未拒斥外来卵；若6天内外来卵消失，或仍留存于巢箱但雌性未对其孵卵（即被埋于巢材下方或不在巢杯内，如图1b所示），则认定该巢雌性拒斥了外来卵（参照Yang等，2015；Liang等，2016；Liu等，2019）。 已有研究表明，弃巢行为亦是宿主鸟类拒斥外来卵的策略之一（Hanley等，2016），但本实验中未观测到巢弃置现象。若实验巢在6天内遭受捕食，则该巢的实验结果将不计入统计。