De Sperwer Accipiter nisus als broedvogel in de provincie Groningen in 2019 en 2020

Since 2012, when a province-wide survey of breeding Sparrowhawks was initiated, some 140 territories have been recorded in Groningen, with another 60 possible breeding sites. Fortunes differ widely, as illustrated by two municipalities that have been monitored since 2012: Sparrowhawks in Haren were largely stable in numbers, whereas those in Leek steeply declined. These trends reflect the overall picture for Groningen, where numbers fluctuate and predation has increased in the course of the years. In the past few years other causes of nest failure propped up, of which the causes remained unknown. Sparrowhawks in Groningen use an wide variety of trees as nesting place, with a preponderance of deciduous trees (partly reflecting availability). Nest success in 2019 was low, and average in 2020, start of laying averaged respectively 28 April and 29 April, also about average for the period 2014- 20. The overall sex ratio for 2014-20 was in favour of males (307 vs. 247), whichdeviates from the country-wide sex ratio which is almost 50-50. The proportion of chicks infested with louse flies varied substantially between years, in 2019-20 for example 26% and 48% respectively. In order to come to grips with the decline and with the wide variations in local breeding success, a colour-ring program for chicks was initiated and trap cameras will be used to detect causes of nest failures.