Philopatry in a reintroduced population of Bearded Vultures Gypaetus barbatus in the Alps

Abstract

Following its eradication in the Alps in the early 1900s, the Bearded Vulture Gypaetus barbatus has been reintroduced in four Alpine regions since 1986. The first successful breeding since this reintroduction into the wild occurred in 1997 in the western Alps, and in 1998 in the Central Alps, thereby establishing two subpopulations. Here, we focus on the growth and the settlement patterns of one of the major subpopulations of reintroduced Bearded Vulture, that of the Central Alps. By 2015 there were 15 breeding pairs in the Central Alps, and the density within the core area was strikingly higher (18.8 pairs/1000 km2) than that outside it (overall density 3.4 pairs/1000 km2). New pairs showed high natal philopatry when settling, with maximum distances of 49.2 km from the nearest release sites. Among identified birds, born or released within the Central Alps, 85% (n = 26) paired and settled within this subpopulation and only four birds emigrated to the west. Three birds immigrated from the east or the west. Both the number of pairs and of offspring increased exponentially between 1998 and 2015. The growth of the Central Alpine subpopulation was characterized by concentric and continuous growth around the release sites. Moreover, there was an increase in the density of pairs within the core area. Possible explanations for the high natal philopatry observed include adaptive genetic components, abundant food resources and conspecific attraction. As a consequence of the substantial population increase, releases in the Central Alpine subpopulation were stopped after 2008. The population has grown almost exclusively on the basis of wild-born birds since then, and has become a major subpopulation of the Bearded Vulture in the Alps.