Seasonal behavioral change and nest-site fidelity of the Eurasian Tree Sparrow during winter in a residential area in Northern Japan

Abstract

The urban biodiversity is a modern concern warranting particular attention. As bioindicators, birds often contribute to the assessment of urban biodiversity; therefore, understanding habitat selection by urban dwelling birds may assist in the maintenance and management of urban biodiversity. However, habitat use by small birds in urban areas on a small scale has been little studied, so far. Here, we aim to reveal where and how the Eurasian Tree Sparrow Passer montanus utilizes a residential area during the winter in Iwate Prefecture, northern Japan. The relationships among sparrow flock size, flock location, nesting site and seasonal changes are the primary focus of our study. Flocks were observed from October 2012 to April 2013. Nests were surveyed during the 2012 and 2013 breeding seasons. Our results revealed that the total number of sparrows and average of flock sizes changed seasonally. In mid-winter, the total number of sparrows was at its lowest, yet the average flock size was greatest. Such changes may have been caused both by severe weather conditions (snow and low-temperatures during mid-winter) as well as by preparation for breeding in early and late winter. Sparrows were not dispersed everywhere, instead they gathered in flocks at particular sites. The average distances between flocks and the nearest nest site were less than 40 m; in fact some old nest sites were used as roost sites. High ranked kernel density areas were located in unpaved areas and/or close to nests, especially in mid-winter. Moreover, new nest sites were commonly constructed within 30 m of old nesting sites. Eurasian Tree Sparrows, it seems, display a level of nest fidelity. Based on such nest-site fidelity it might be possible to control future nesting sites of Eurasian Tree Sparrow through the provision of nest boxes.