VAN BREDERODE N. & H. ROERSMA (2015) After almost 80 years Peregrines Falco peregrinus return to ground nesting on the Dutch Frisian islands of Rottum. LIMOSA 88 (3): 105-113.

During their increase after the DDT era, Peregrines initially bred only in nest boxes and other high altitude nest sites on the Dutch mainland (since 1990). Although the nearest such nest was only 29  km away, it was a female fledged on the German Frisian island Trischen, Schleswig-Holstein, that first bred on one of the uninhabited islands of Rottum and did so for seven successive years (Tab. 2). Since 2005 Peregrines have bred on the ground on two islands of the Rottum group. Their breeding success (on average 2.5 fledged young per nest) did not differ from that on the mainland (Tab. 3). Although in both localities egg loss is the main cause of breeding losses, its cause is very different. While on Rottum eggs simply fail to hatch, losses on the mainland are mainly due to external factors like territorial fights, accidents with instable and exposed old crow nests or disturbance by hybrid falcons. Breeding success on Rottum was higher than that of ground breeding Peregrines on the German Frisian islands. Here egg loss (by unknown causes) is also the main cause limiting numbers of fledglings. In the next few years it will be interesting to see whether new breeding pairs will concentrate on uninhabited islands or will first spread out to all Frisian islands and then squeeze in. In 2014 a pair bred (unsuccessfully) on the nearby inhabited island of Schiermonnikoog.

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