Romke Kleefstra (2024) Tens of breeding Short-eared Owls Asio flammeus again in the Dutch province of Friesland in 2023. LIMOSA 97 (3): 137-141.

In both 2014 and 2019, an outbreak of Common Voles Microtus arvalis led to dozens of breeding cases of Shorteared Owls in the Dutch province of Friesland. In 2014 there were an estimated 50 pairs, in 2019 there were at least 75 breeding cases. In the autumn of 2022 and the following winter, signs of a new vole outbreak were visible, but due to a relatively wet January and a soaking wet March in combination with short periods of frost, Common Voles appeared to have become a lot scarcer during the course of March. Nevertheless, there remained places with clusters of active voles. Although this was not on the scale of the vole outbreaks in 2014 and 2019, tens of Short-eared Owls still came to breed in Friesland.
A total of 54 territories were recorded in Friesland (Fig. 1). The vast majority of Short-eared Owls nested on peat soil, most pairs bred in intensively agricultural rye grassland (Tab. 1). The average clutch size was 6.7 eggs per nest. Laying started on average on 2 May (Tab. 2). Of the total of 29 nests found (including 2 subsequent clutches), 17 failed. From 13 successful nests in the interior of the province of Friesland, approximately 68-75 young fledged, of which 58 were ringed.
At the national level, the province of Friesland stands out with the number of Short-eared Owl pairs during vole-rich years. Of the 75 breeding pairs counted in the Netherlands in 2014 for example, 53 were in Friesland, and of the 90 breeding pairs counted in 2019, 75 were in Friesland. In addition to the 54 breeding pairs counted in Friesland in 2023, at least 6 territories were found elsewhere in the country. This short contribution compares the results with those from 2014 and 2019 and takes a closer look at the outbreaks of Common Voles and the invasions of (breeding) Shorteared Owls over the past 20 year

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