Sex-related variation in metabolic profile of two wagtail species

Progression of the vernal migratory life history stage to breeding presents a number of different behavioral and physiological changes. Long-distance passerine migrants deposit substantial fat stores to fuel their migratory journey. Many of those migratory birds arrive at their northerly breeding grounds with larger fat stores than other birds. In the current study, plasma metabolites were used to determine refueling rates in two species of songbirds at stopover sites in New Damietta, Egypt and to test the hypotheses that males refuel faster than females during spring. The results showed that males usually refuel in higher rates than females during spring in both species. The results show that sex-related variations in stopover refueling rate can be a possible mechanism for protandry in spring and faster male migration than females.