<b>Breeding barn swallows recognize householders from strangers</b>

This study was conducted from May to July 2017 in Caoyang Village, Nanxing Town, Leizhou City, Zhanjiang, Guangdong Province, southern China (20°50′ N, 110°09′ E). Nanxing Town covers a total area of 135 km² and consists of 127 villages with a population of 108,000 as of 2014. The total area planted with crops is 10, 018.2 ha, of which 8, 333.33 ha are dedicated to rice, producing nearly 50,000 tons of grain annually, making it an important grain production base in Leizhou (www.leizhou.gov.cn). The local architectural style mainly consists of single-story brick and wood houses with tiled roofs. barn swallows (<i>Hirundo rustica</i>) usually nest along the cornices of corridors that are open on two sides and connected to the front and back courtyards, making them suitable for experimentation.Before the experiment began, we conducted a survey of barn swallow nests in the breeding phase throughout the village and trained householders on FID measurements to ensure that they approached the experimental subjects at a consistent walking pace. Both householders and experimenters wore neutral clothing. The observer would wait at a fixed point 10 m directly below the nest until the parent birds returned and then immediately begin approaching them. To minimize noise interference, the observer remained silent throughout the process. Measurements were performed using an SNDWAY SW-70G rangefinder (Sndway Technology (Guangdong) Co., Ltd., Dongguan, China) with an accuracy of 0.001 m. This fixed starting distance served to mitigate any correlation between the FID and starting distance (Møller et al. 2019). The FID was recorded as the horizontal distance between the person’s position and the spot directly below the nest when the parent bird flew away, as described by Blumstein (2006).YL, as the sole control experimenter, also recorded the date, number of returning parent birds, and, if possible, noted any behaviors displayed by the householders toward the barn swallow nests, with special emphasis on cases where householders were frequently present. Repeatability analysis indicated consistent FID estimated among observers within the same type of personnel (Guay et al. 2013).Our results demonstrated that barn swallows can identify the householder where their nest is located, displaying lower alertness when the householder approaches, compared to an unfamiliar experimenter. Furthermore, there was no significant difference in FID between swallows reacting to householders who were rarely at home versus those who were frequently present, suggesting that barn swallows may possess the capability to recognize and retain memory of individual humans over time. Our findings provide evidence that barn swallows exhibit remarkable cognitive abilities. The long-standing symbiotic relationship between barn swallows and humans provides a unique model for studying the adaptation of species to environments with close human interactions. Research on their behavior and survival strategies can offer insights into the influence of symbiotic relationships on species adaptability and evolution.