Habitat effects on bird surveys: a simultaneous experiment using Point Count and active Audio Recording in a Mediterranean protected area

Habitat structure can affect species detectability and the performance of bird survey methods, particularly in heterogeneous habitats, as variation in vegetation complexity can affect both visual detection and sound attenuation. However, a clear understanding of how habitat structure interacts with survey methodology to shape detection probability remains limited, especially in structurally diverse ecosystems such as the Mediterranean. To evaluate this, we conducted a simultaneous count comparing two survey methods, Point Count (PC) and active Audio Recording (AR), to assess their effectiveness in measuring spatial variation in bird species richness across three habitat types with different vegetation typologies: pine-wood, ecotone/open habitat and sclerophyllous forest, within a protected area in central coastal Italy during the 2021 breeding season (May-June). We hypothesized that (i) PC and AR would differ in detected bird species richness, and (ii) this performance could be influenced by habitat type, resulting in species richness varying between methods depending on habitat structure. We surveyed 37 sites using both methods simultaneously, with two replicas per site, totaling 74 sampling units. Species richness varied with habitat type, being highest in ecotone and open habitat and lower in pinewood and sclerophyllous forest, a pattern consistent across survey methods. Non-vocalizing birds, detected exclusively through PC, affected method performance only at the habitat level, with no overall effect across all sampling points combined. With the applied sampling effort, both methods reliably reflected spatial variation in species richness, confirming that AR can serve as an effective tool for assessing relative bird diversity across habitats. Moreover, this simultaneous experimental approach offers practical guidance for future bird monitoring programs, particularly for biodiversity assessments in heterogeneous habitats.