Evaluating the importance of managed forests as habitat for the Semi-collared Flycatcher (Ficedula semitorquata)

Intensive forest management has caused a decline in the numbers of birds specialized on old growth. Understanding how forest stand attributes influence the distribution of these specialists has hence become a prerequisite for sustainable forest management. In this study, we evaluated the conservation value of managed forests for old-growth forest specialists using the poorly studied Semi-collared Flycatcher as an example. We applied a boosted generalized additive model to identify forest characteristics that determine the occurrence of the bird in Bulgaria. We found that on a national scale, forest stand age and percent cover of broad-leaved forests best explain the breeding distribution of the flycatcher. Although, forest stands became suitable habitat at an age of around 70 years for this species, stands in the interior forest featuring trees older than 160 years and composed of more than 80% broad-leaved trees were preferred by the species. At a local scale, the amount of dead wood positively influenced nest site choice of the flycatcher. In total, 22.3% of all studied broad-leaved forests in Bulgaria showed a predicted habitat suitability higher than 50%. High-stem forests that are old enough to develop old-growth characteristics had the highest potential to serve as habitat for the Semi-collared Flycatcher in Bulgaria. Therefore, we conclude that a decrease in logging of forests stands older than 160 years decreases the risk of decline of the Semi-collared Flycatcher.