Detection of otter (Lutra lutra L.) signs in a survey of Central and Eastern Poland: methodological implications
Searching for spraints (excrements) and tracks is widely used for monitoring of European populations of otters Lutra lutra. Data collected in Central and Eastern Poland were analysed in order to evaluate the environmental factors affecting the detection of otter signs during field surveys. At each out of 1111 sites studied from 1996–1998 numbers of otter spraints and tracks as well as distance searched to detect first sign were noted. At each site several environmental variables were recorded to identify factors that may have affected the survey results. The variation in numbers of spraints and tracks found at each positive site was not related to the habitat quality and any other habitat features (including tree and shrub cover, presence of potential shelters) analysed, except the number of tracks was positively related to bridge potential. The distance searched was the most variable indicator of otter occurrence. It increased with the width of river and at sites with few potential sprainting sites, with bridges of poor potential or with no bridges at all, and where many signs of human and domesticated animals activity were noted. The results indicate that detection of otter signs is partially affected by specific elements unrelated to habitat potential and therefore numbers of spraints should not be used as an indicator of otter habitat preference. At a regional scale variation in number of spraints and tracks, as well as distance searched was related to otter occupancy expressed in the form of percentage of positive sites at three study areas. This study shows that measuring the distance searched provides additional indication of otter status at a regional scale and could be used to identify specific habitats where detection of otter signs during surveys is difficult.
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