Variation in small mammal food resource niche metrics of Western Barn Owl (Tyto alba) at the nesting pair and local population level

In the present study, we investigated food resource niche parameters and the degree of specialization of two local Western Barn Owl (Tyto alba) populations in two different demographic phases as the crash (2015–2016) and outbreak (2019–2020) of the Common Vole (Microtus arvalis). The study was conducted in two parts of the Transdanubian region of Hungary, namely in Duna-Drava National Park (DDNP) in the southeastern part, and in Fertő-Hanság National Park (FHNP) in the north-western part. For the analysis, we used food consumption data of 20–20 randomly selected breeding pairs from the DDNP population, while 14 and 17 breeding pairs in FHNP population in the crash and outbreak periods, respectively. Since the small mammal consumption of owls represented 99.3% of the total number of individuals, only data of small mammals as main food resource were taken into account during the analysis. Based on a trait-based framework which taking into account the resemblance between resources, Rao’s quadratic entropy metrics was used to estimate the food resource niche breadth at local owl populations and the breeding pair level. The small mammal resource utilization of owls was dependent on populations. The niche breadth of DDNP population was significantly smaller than FHNP population. The estimated niche overlap at the individual level was significantly different between the two populations. The calculated value of specialization of barn owl populations was significantly higher in north-western than south-eastern population. The niche breadth of the owl population living in the DDNP was significantly higher during the crash period. In contrast, the estimated niche breadth of the population living in FHNP did not differ significantly between the two demographic phases. Based on our result, the applied trait-based framework of resource niche pattern analysis demonstrated that the differences of niche breadth were explored in more detail by this method between the local Barn Owl populations of different geographical region.