Predatie door vogels en zoogdieren op een grote zwerm Spreeuwen Sturnus vulgaris bij een slaapplaats in riet

In late February 2016, a flock of 55.000-100.000 Starlings was observed roosting in a reedbed near Kollumeroord, Lauwersmeer, northern Netherlands (53.324 N, 6.180 E). The flock showed up just before sunset and was under attack from sunset until at least one hour after sunset by several Sparrowhawks Accipiter nisus and Goshawks A. gentilis, and by mammals (presumably Pine Marten Martes martes). Remains of depredated Starlings were collected and sexed, aged and categorized as taken by a raptor (feathers plucked, intact) or a mammal (feathers bitten off, torn). In total 36 preys were found, which showed similar proportions of second calendar year birds and adults, both in raptor and mammal preys. Most prey items were male (68%) and this bias was mostly found in preys of mammals (72% male), but the difference with preys of raptors (62% male) was not significant. These data suggest that raptors (“aerial predators”) and mammals (”ground predators”) do not differ much in the age- and sexspecific selection pressures that they impose on a Starling flock roosting in a reedbed. However, the sample was quite small and more prey items are planned to be collected to further explore a possible conflict between the individual and the flock as a whole when choosing a roost site.