Nest Box Bacterial Loads Are Affected by Cavity Use by Secondary Hole Nesters

Simple Summary Nest box bacterial loads were studied during the prebreeding period in relation to nest box occupancy by Great Tits and Blue Tits in the previous season at two different study sites: an urban park site and a deciduous forest site. This analysis revealed that the interior bacterial load was higher in the nest boxes used in the previous season for breeding; however, the results were significant only in the forest area. In general, the bacterial load was significantly higher in the nest boxes placed in the forest study area than at the urban park site.Abstract Among the environmental factors that affect bird nesting in nest boxes, the influence of microbial communities is relatively poorly understood. In this study, nest boxes used for breeding by secondary cavity nesters were sampled before the start of the breeding season to assess the bacterial loads of the nest box in relation to their previous year status. Different parts of the wooden nest box offer variable conditions for the development of bacteria. During the breeding season, the nest box entrance hole is wiped out by birds, delivering bacteria to their bodies, but during winter, it is exposed to unfavourable external conditions. The interior of the nest box, in turn, is also wiped by birds, but the conditions during winter are more stable there. Therefore, samples from the entrance hole and the interior of the nest box were taken at two different study sites: an urban parkland and a natural forest. We predicted that both the occupancy of the nest boxes during the previous breeding season by birds and the nesting sites would influence the bacterial load of the nest box. To verify this prediction, two categories of nest boxes were sampled at both study sites: nest boxes occupied by any of the two tit species (Great Tit or Blue Tit) in the previous season for breeding and nest boxes that had remained empty that year. The interior bacterial load of the nest box was higher in the nest boxes occupied in the previous breeding season, but only in the forest area. Furthermore, the bacterial load of both the entrance hole of the nest box and the interior was significantly higher in the forest study area in both occupied and unoccupied nest boxes. Our results show that the bacterial load of the nest box is positively related to the presence of nests in the previous breeding season and can vary between different sites.

Automated summary

This study investigated the bacterial loads of nest boxes and found that the interior bacterial load was higher in the nest boxes used for breeding in the previous season, especially in the forest area. The presence of nests in the previous breeding season and the study site influenced the bacterial load of the nest box.