Stopover dynamics of 12 passerine migrant species in a small Mediterranean island during spring migration

Small coastal islands offer landing opportunities for large numbers of migratory birds following long sea crossings. However, they do not always provide sufficient refueling opportunities, thus raising questions about their importance for the success of migratory journeys. Here we analyzed a large dataset collected during 3 years of captures and recaptures of 12 species on the island of Ponza, central Italy, to determine the importance of the island for refueling. Despite the very large amount of birds on the island, only a very small fraction (usually below 2%) stayed on the island for longer than 1 day. These birds had low energy stores and, in most cases, they were not able to successfully refuel on Ponza. Only two species (Subalpine Warbler and Common Chiffchaff) had a positive fuel deposition rate, possibly as a result of the better suitability of the island's habitat to these two species. We underline that the large use of the island despite the relatively low refueling opportunities may be due to other aspects that it may offer to the birds. Possibly, birds just landed after a long sea crossing may require a short rest or sleep and can find opportunities to do that on the islands, reinitiating their onward flight after just a few hours. Understanding the role of these islands for migratory birds will be important for conservation, since setting priorities for protection might be misled if considering only refueling success as an important variable.