Forty years of dietary studies on barn owl (Tyto alba) reveal long term trends in diversity metrics of small mammal prey

in Animal Biology
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The diet of predators is influenced by local conditions (e.g., characteristics of habitat and microhabitat, seasonality, prey availability) and therefore tends to change across time. In this paper, the diet composition of the barn owl (Tyto alba) in Italy was studied using a meta-analysis of 47 articles (covering 212 independent sites, with multiple surveys for some sites, thus giving a total of 290 datasets) between 1972 and 2012. General Linear Models were used to assess the effects of year and study site on four distinct diversity indices (species richness, dominance, Shannon-Weaver diversity and equitability). The year of data collection was a factor used in all analyses. Year had a greater effect than study site on all diversity indices, but the effect was not significant for the evenness and the species richness. However, dietary dominance increased significantly over the years, the Shannon-Weaver index of diversity decreased significantly over time, and equitability also decreased significantly over time. The relative abundance of various species of rodents did not increase/decrease progressively over the years, although there were inter-annual fluctuations. On the other hand, the relative abundance of insectivores tended to decrease with time, and there was a significantly negative correlation between year and the frequency of consumption of Sorex spp. and a marginally significant negative correlation for Crocidura leucodon.

Forty years of dietary studies on barn owl (Tyto alba) reveal long term trends in diversity metrics of small mammal prey

in Animal Biology



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    Geographical position of the various study sites from which owl pellet literature datasets were used.

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    Correlations between year of Tyto alba pellet collection and dominance (graph A), Shannon index of diversity (B), and equitability (C). For statistical details, see the text.

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    Patterns of the average yearly values of the various indices of taxonomic diversity of Tyto alba diets.

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    Correlation between year and the frequency of occurrence of Sorex sp. remains in Tyto alba pellets. For statistical details, see the text.

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    Correlation between year and the frequency of occurrence of Soricomorphs remains (all species pooled) in Tyto alba pellets. For the statistical details, see the text.

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    Values of the various indices of taxonomic diversity of prey taxa inside Tyto alba pellets in relation to the year of collection.

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