COVER LETTER
On behalf of all coauthors, I am submitting a manuscript titled ‘Habitat-specific variation in bacterial loads of wooden nest boxes in the pre-breeding period’ for possible publication in Ecology and Evolution. The manuscript is new, approved by all coauthors, and is not considered for publication elsewhere. This study is a research article and is a continuation of our previous work (Zabłotni, A., Kaliński, A., Bańbura, M., Glądalski, M., Markowski, M., Skwarska, J., Wawrzyniak, J., & Bańbura, J. (2020). Experimental nest replacement suggests that the bacterial load of nests may mediate nestling physiological condition in cavity nesting Great Tits (Parus major ). Journal of Ornithology , 161, 819-828) on the influence of bacterial loads on hole-nesting passerines. This study presents observed differences in bacterial loads in nest boxes located in two distinct habitats: urban parkland and natural forest. We showed that the bacterial load was on average higher in the nest boxes at the forest study site. We assume that this result is related to differences between habitats, including the composition of plant species in parkland and forest. We also showed that the presence of the nest in the nest box in the previous season positively affected the bacterial load, but only in the forest area. The results presented are relatively novel and supplement our understanding of the factors that potentially can affect the breeding performance of birds using artificial nest boxes with a new dimension related to microorganism-host interactions. Therefore, we consider Ecology and Evolution to be the most appropriate journal to publish the findings.