SCHEKKERMAN H, HUSTINGS H. VAN DEN BREMER L, KAMPICHLER C, VAN WINDEN E, BROERE M & DE VRIES H (2015) Wintering Great Grey Shrikes Lanius excubitor in the Netherlands: detection, numbers and distribution. LIMOSA 88 (1): 11-21.

Numbers of wintering Great Grey Shrikes (mainly from Scandinavia) in the Netherlands declined during the late 20th century. Since then a recovery became apparent, but numbers remained poorly known. In 2007/08-2012/13, nationwide surveys were organised through the website Waarneming.nl. Volunteer observers were asked to search predefined areas for shrikes in two weekends per winter, and also report all other observations. We used data from sites counted twice and a binomial mixture model to estimate the number of birds present and the probability with which these were detected during a count (Tab. 1), and the ratio between the total number of birds reported from the doubly counted sites to the estimated number present to translate reports from elsewhere into numbers present. The detection probability was estimated at 53% on average. As this assumes a closed population, individual movements between counts may have caused some overestimation of numbers, but the result indicates that a conservative approach requiring observations in both December and January for acceptance of a winter territory (Tab. 2) results in an underestimate. We estimate that 150-300 shrikes winter in the Netherlands in poor, and 400-650 in good years (Tabs. 2 & 3). Variation between winters was larger in ‘peripheral areas’ in coastal dunes, marshes and low-intensity farmland in the lower parts of the country than in the heathlands and peat bogs on higher sandy soils, where most birds winter. Winter point counts since 1980 and non-systematic observations reported through the website also show large variation in abundance between years, which was correlated with the Swedish breeding population index and the numbers observed leaving that country on autumn migration at Falsterbo. These data also confirmed an increase since the turn of the century, with 4% per year on average. The long-term decline followed by a partial recovery seem to mirror the development of the Swedish breeding population over the past decades.

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