The role of nest-box density and placementon occupation rates and breeding performance: a case study with Eurasian Blue Tits

Abstract

The use of nest-boxes to study bird breeding biology, as well their use as a management tool, is widespread. The exact placement of nest-boxes may affect individual preference for these breeding sites; however the influence of determinant factors (e.g., nest-box density) in occupation rates or breeding parameters has not been sufficiently covered. Here, we used the Eurasian Blue Tit as a model species to determine factors influencing nestbox selection in a transformed habitat: a pine plantation. Our study design consisted of 100 nest-boxes arranged at different heights (positioned "high" at 3.0-5.0 m, or positioned "low"at 1.5-2.0m), andwith different degrees of clustering (clustered in groups of 6, or isolated by at least 80mfrom the nearest nest-box).We calculated the potential territorial area for each nest-box and the distance to the nearest neighbour.We investigated the influence of nest-box position and breeding pair density on occupation rate and breeding success, controlling for habitat structure. Eurasian Blue Tits preferentially selected nestboxes located high on the tree and with fewest neighbours. Laying date was earlier in higher nest-boxes and in those with fewer neighbours and at a greater distance from the nearest neighbour. The number of nestlings was positively related to shrub cover andmedium tree height. Fledgling mass was higher when distance to the nearest neighbour was greater and fledgling tarsus length was positively related to oak-species abundance. Our results suggest that disentangling the important factors for nest-box placement and spatial dispersion in the landscape is important to adapt to species-specific requirements in each given habitat.