Before embarking on a migratory flight, birds often exhibit extreme changes in their feeding behaviour and gut physiology, such as increased feeding, digestive organ remodelling, and shifts in diet. Many passerine species switch from insects to fruits during autumn migration, but we do not known if such a dietary switch occurs during spring migration in temperate zones, when fruit production typically is rare.

During our spring fieldwork on the island of Ponza (Italy), we discovered two plants, Prasium majus and Rhamnus alaternus, that produce fruits in spring. We monitored the fruiting season of both plants and collected faecal samples of six different passerine species to understand whether birds use the available fruits as a refuelling resource in spring. We found that the fruits of P. majus were generally preferred by all species, and garden warblers (Sylvia borin) had the highest occurrence of seeds of both plants in their faeces. The availability of ripe P. majus fruits increased over the spring migration season and was positively correlated with the number of faecal samples containing seeds.

Our work reveals a so far overlooked relevance of P. majus and R. alaternus fruits as spring stopover refuelling resources for at least five ‘normally insectivorous’ passerine species at a temperate zone stopover site. Frugivory may represent an easy way for birds to rapidly acquire water, micro-, and macronutrients during spring migration, particularly at stopover sites such as Ponza which are poor in resources and where birds typically stop over for short time periods. Fruit consumption may help individuals to quickly resume migration to reach their breeding grounds or stopover places richer in nutrients.

The full article can be found in Ecology and Evolution http://dx.doi.org/10.1002/ece3.72239.