Heterospecific social attraction in migrant birds: Habitat niche overlap between two threatened shrikes

Context: Effective biodiversity conservation requires information about a species' ecology and its relationship with the geographical context. To achieve this efficiently, species distribution models can be developed, also taking into account species associations. Aims: I aimed to illustrate the habitat requirements of two threatened passerines of semi-open landscapes, i.e. the lesser grey shrike, Lanius minor, and the woodchat shrike, Lanius senator, in southern Italy. Further, I assessed whether there is heterospecific social attraction between them, by assessing how their habitat niches overlap. Methods: Data were collected by territory mapping during the 2009-13 breeding seasons. The habitat requirements of the species were investigated with the help of ecological niche factor analysis (ENFA). In addition, the areas of sympatry between the two species were defined by indicator kriging and the habitat niche overlap was analysed using the generalised linear model (GLM). Key results: The results showed that these two species inhabit open areas, with scattered vegetation such as shrubs and trees, while avoiding intensively cultivated permanent crops, such as vineyards and olive groves. Moreover, a little difference was observed in the percentage cover of shrublands, which were higher in the woodchat shrike territories than in the lesser grey ones. The strong overlap in their habitat niches suggests heterospecific social attraction between them, especially because of the species rarity. Conclusions: The lesser grey and the woodchat shrike were found to occur in very similar environments, by evidencing the overlap of their macrohabitat niches. This suggests the presence of heterospecific social attraction, corroborating the understudied hypothesis that this phenomenon is valid for migrant birds as well. The lesser grey shrike, in particular, may use occurrences of the woodchat shrike as a cue for assessing habitat quality and, thus, to establish its territory. Implications: Considering the high habitat niche overlap, habitat changes occurring in the landscape might affect them equally. Furthermore, the use of heterospecific social information in habitat selection potentially has many important conservation implications. Indeed, by reproducing the appropriate information, birds could be attracted to specific sites known to be high-quality habitat.