The Impact of Snags and Logs on the Bird Community in the Non-breeding Season in Golestan National Park

This study investigated the effect of density and other properties of dead trees on the bird community in Golestan National Park during the autumn of 2013. Birds and various environmental variables were detected within a 25 m radius of each of 100 sampling points. The relationship between biological diversity and the relative abundance of bird species to the environmental variables related to the dead tree characteristics was evaluated. To determine the association of bird diversity indices with environmental variables, a canonical correspondence analysis (CCA) was performed. The first axis of CCA successfully separated the two groups of birds. The first group of birds comprised the Lagea Rock Nuthatch, Black Woodpecker, Winter Wern, Nutatch, Great Tit, Great Spotted Woodpecker, Erosian Jay, Nightingale and Common Blackbird which had a positive correlation with some factors of dead trees, such as: the first and second axes of standing dead trees (snags) and fallen dead trees (logs), wood surface conditions of snags, degree of decay of logs, height at which food is found of snags, condition of canopy in snags, length of logs and presence of nests. The second group was on the right-hand side of the axis and included such species as: Coal Tit, Song Thrush, Long-tail Tit, River Warbler, Flycature, Green Woodpecker, Stonechat, Hawfinch, Pheasant and Common Chiffchaff. These birds had a positive correlation with the following environmental variables: the third and fourth axes of logs and the fourth axis of snags.