Species with similar ecological characters often compete with each other; however, a species may also facilitate the survival or reproduction of another ecologically similar species although such interaction is rarely documented in birds. Here we reported a facilitative species interaction between Asian house martins (Delichon dasypus) and russet sparrows (Passer cinnamomeus), both passerines using closed nests, in a montane farming area of Taiwan. We found that Asian house martins constructed dome-shaped nests in human houses that provided additional nest sites for russet sparrows, secondary cavity-nesters with greatly declining populations in Taiwan. Russet sparrows that used house martin nests had reproductive success comparable to those that used artificial nest boxes. However, Asian house martins avoided reclaiming sparrow-used nests, which reduced their available nest sites. Interestingly, our results imply that man-made structures may be used as a conservation tool to improve the breeding of the endangered russet sparrows via this facilitative interaction.

We checked the nests of Asian house martins in the mornings using an endoscope. We recorded the status of the nests (occupied by russet sparrows or Asian house martins) and the numbers and developmental stages of eggs and chicks in each brood. The survey was done at regular intervals in 2020 and 2021 (once every 3-4 days in 2020 and daily in 2021) and at irregular intervals in 2019.  We defined the developmental stage of “fledging” as: 1) one chick that was at least 12-days old was found in the nest (Yang et al. 2012), and 2) an empty nest with no chick carcass nearby, suggesting the chicks had successfully fledged rather than being predated.

The dataset files can be opened by Excel.  The datasets files were used to generated Fig.2 and 3 of the paper entitled "The role of a synanthropic bird in the nest niche expansion of a secondary cavity-nester to man-made structures".