VAN BOEKEL W (2017) Changes in the diet of Barn Owls Tyto alba after the flooding of the nature reserve De Onlanden. LIMOSA 90 (2): 51-59.

The nature reserve De Onlanden, located in the northern part of the Netherlands, was assigned to become a water containment area in order to prevent flooding in the surrounding areas, specifically the city of Groningen. In January 2012, the area was flooded and suddenly changed from a meadow to a marshland area. This major habitat change had a large effect on the populations of small mammals in the area. The Common Vole Microtus arvalis, which was the dominant species before the flooding, disappeared almost completely. Numbers of shrews, especially Common Shrew Sorex araneus and Water Shrew Neomys fodiens, became the dominant small mammal species.
The diet of Barn Owls living inside and nearby the nature reserve was studied before (2005-2011) and after (2012-2015) the habitat change, by pellet analysis. In The Netherlands, Barn Owls largely depend on Common Voles as their main prey.
The portion of Common Voles in the diet of Barn Owls in De Onlanden decreased from 65% to 20% throughout the study period. Other prey species, like Field Vole Microtus agrestis, Harvest Mouse Micromys minutus and Water Shrew, increased. These changes in diet were not observed in Barn Owls living in areas just outside De Onlanden or, on a larger scale, Barn Owls breeding in the northern part of the Netherlands. Since 2012, the number of Barn Owls roosting in De Onlanden decreased. In 2016 only three regular roosting locations were still in use.
The decline of the Common Vole population in De Onlanden, as a result of the large-scale habitat change in this nature reserve, had a strong effect on the diet of the local Barn Owl population in De Onlanden, and resulted in a decrease of the Barn Owl population using this area.


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