De Havik Accipiter gentilis als meeuwenpredator op Texel

On the Dutch Wadden Sea island of Texel (15.971 ha, of which 10,386 ha farmland, 2969 ha dunes and 538 ha woodland), the Goshawk arrived as a breeding bird in 1997 (1 pair). Since then, the local population increased steadily to 11-15 pairs annually in 2002-2014 (1-6 pairs in farmland, 5-6 pairs in woodland, 2-5 pairs in dunes). In a plot of 8 ha in the dunes of Kelderhuispolder, where gulls are being studied since 2006, Goshawks were at first recorded infrequently but later on with increasing frequency until the first pair settled in 2012. This pair hunted, among others, adult gulls, although real kills were rarely witnessed (3 kills on 153 visits to the colony, during 389 h of field observations). In 2013, this pair nested in a Sambucus at a height of 2.0-2.5 m above ground level. On 4 May 2013, the nest contained 4 eggs. Recent plucks included Rabbit Oryctolagus cuniculus and Water Rail Rallus aquaticus. At first, the hawks just caused disturbance in the gull colony (mixed Larus agentatus and L. fuscus), but depredation of chicks was recorded on 29 June 2013. All together, only two chicks were found killed by Goshawks within the enclosure, a 23-day old chick of Herring Gull and a 3-day old chick of Lesser Black-backed Gull (the latter at most 75-80 g when killed), but other traces underneath the nest indicated that several more chicks must have been depredated (pellets, ring). Total predation of chicks was much higher, especially in 2013 when 29 out of 47 Herring Gulls chicks were depredated, and 36 out of 51 Lesser Black-backed Gull chicks. The range of potential predations includes – apart from Goshawks - Feral Cat Felis catus, Ermine Mustela erminea, Buzzard Buteo buteo, Marsh Harrier Circus aeruginosus and Kestrel Falco tinnunculus, but the majority of kills related to cannibalism (either intra- or interspecifically). Leftovers of Goshawk kills typically lacked the head and flight and body feathers; only the breast muscles had been removed. This contrasts with cannibalistic kills, in which typically guts, stomach and leg muscles are removed (but never breast muscles).