Local prior information and mainland overflow explain avian colonisation in a major land-bridge island

Abstract

Aim: The relative roles of intrinsic and extrinsic factors, and those of local and regional variables, in island colonisation, remain major biogeographical questions. Thus, we analysed avian colonisation records of a large land-bridge island, defining successful colonisation as the occurrence of breeding during at least 3 consecutive years, at species level with the aim of identifying the main determinants of island colonisation by birds. Location: Mallorca (Balearic Islands, western Mediterranean). Major Taxa: All avian species recorded in Mallorca Island. Methods: We performed logistic regression by fitting generalised linear mixed models to data. We explored seven explanatory variables and performed model selection based on Akaike's information criterion. Results: A total of 26 bird species colonised the island during the study period, a rate of ca. 0.7 colonising species/year. Only seven species were found to attempt colonisation unsuccessfully. Bird species with the highest colonisation probabilities were those with growing population trends on the mainland and a previous status as wintering species on the island (0.58), followed by wintering species with a stable population trend on the mainland (0.37). Main Conclusions: The high rate of colonisation indicates that the process of incorporation of new species has been very dynamic. Colonisation was dependent on a local factor (having prior information about the island) and a regional factor (density dependence on the nearby continent). However, it was not influenced by body size, diet, habitat or IUCN level of threat. Based on the results of our modelling, we present a predictive list of likely future colonisers.