Are certain habitats better every year? A review and a case study on birds of prey
Although habitat studies are essential for species management, little is known about temporal and spatial variation in the wildlife-habitat relationships. This paper explores annual variation in habitat preferences of and relative quality for diurnal raptors and owls. A review of 772 published sources showed that habitat×year interaction had been analysed in only 10% of habitat quality and 5% of habitat preference studies. Two major factors behind the year-effects were the fluctuations in rainfall and prey base, which together influenced a wide variety of species. Yet, 67% of studies had pooled data from different years and 17% relied on data from only one year. The conclusions of the review were validated by analysing a typical situation for which habitat×year interactions could be expected – habitat quality in a vole-specialized raptor, the common buzzard Buteo buteo, in an area of regularly fluctuating vole abundance. According to eleven-year data, the relationships between buzzard productivity and landscape characteristics were distinct between years. Habitat impact was more clear during vole-poor years, when successful buzzards bred in landscapes having diverse land cover, no wetlands and no conspecifics around. In contrast, during vole peaks, better young production was related to homogeneous landscapes. When years were pooled, the relationships were concealed and habitat quality model became not significant. Selecting ‘‘poor-year habitat’’ or ‘‘rich-year habitat’’ seemed to give a similar reproductive output for the buzzards in the long-term. The results indicate that one-year approaches to wildlife-habitat relationships can easily lead to erroneous conclusions, significant habitat relationships may become lost in pooled data, and the most typical situations that need annually explicit approach can be recognized while planning the studies.
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Document Type: Research Article
Publication date: October 1, 2003