Nest-tree species and breeding success of the Striated Heron in an urban park

Abstract

The Striated Heron Butorides striata is a nearly cosmopolitan species except for North America. Available information on the breeding biology is scarce, including breeding success. I studied the species’ preferred nest-tree species, the number of breeding pairs, and the breeding success of this heron in an urban park of Utsunomiya, central Japan, from 2012 to 2019. The aim of this study was to collect basic data about the breeding biology of this heron species, and to observe the relationship between changes in nest-tree species and breeding success. The number of heron pairs gradually increased from five to twelve pairs from 2012 to 2016, but thereafter decreased from seven to five pairs. A total of 113 nests were observed during the survey period, and the number of fledglings per nest varied significantly among survey years. The nests were built on high branches, averaging 17 meters above the ground. The heron preferred Cedar Cedrus deodara as nest-trees from 2012 to 2014. From 2015 to 2019, most of the nests were built on the Zelkova Zelkova serrata, and breeding success decreased during this time. With the change in nest-tree species, nesting sites were gradually moved within the park. The author recorded the cases of predation by Large-billed Crows and by mammals, as well as nests being blown down by strong winds. In most cases, however, the cause of breeding failure was unknown.