Assessing the Impacts of Tehran- Mashhad Asian Highway on Bird Community in Golestan National Park

Road networks extend their impacts on the surrounding habitats along a variable distance, affecting birds living in natural environments. This study identified the threshold distances upon which a road, located across Golestan National Park, altered the abundance patterns of the native avifauna. Species diversity indices, bird density, and association of birds with environmental variables which are potentially sensitive to human disturbances were studied by distance sampling method and ordination procedure. Birds and environmental variables were detected within a 25 m radius of each of 180 sampling points. To determine the bird species density and association between environmental variables and bird community in different distances from the road, distance sampling method and canonical correspondence analysis was performed, respectively. Nearby road affected the species diversity and distribution of birds in the study region. The effect of road was variably negative, although threshold distances to roads varied among different groups of bird species. The bird community of some species such as woodpeckers, nuthatches, thrushes, wood pigeon, wren, and treecreeper was the most sensitive group to the influences from nearby road. Moreover, the most significant impacts of road on bird community occurred within 500 m of the road edge to the forest interior. The second group, including tit species, showed higher resilience to deleterious influences from nearby road. It would be desirable not to build new road developments within the fragmented area of this region, because their existence would add negative effects on the native bird fauna (e.g. on woodpeckers as umbrella species), considering the buffer distances, particularly 500 m from roads which demonstrate the most significant impacts.