Migration_onset_scolopacidae

Understanding the mechanisms that trigger the onset of migration is of crucial importance given ongoing climate change, particularly as there are possible carry-over effects on population dynamics. The relative contribution of endogenous and external conditions on the decision to start migration is still not well-understood because there are contrasting results in the literature while it is difficult to tell if this is due to species differences or methods, e.g., the timescale considered. Here, we evaluate the effect of individual characteristics, photoperiod and weather conditions on the migration onset of two species, using data from 106 Scolopax rusticola (Eurasian Woodcock) and 87 Gallinago gallinago (Common Snipe) fitted with transmitters. We considered two different timescales. We found that weather conditions are diving Woodcock movements, but no weather conditions correlate with migration onset of Snipe. We discuss main hypotheses which could explain intriguing difference between these two species of Scolopacidae and suggest that the molt schedule of Snipe may result in a trade-off between choosing the best environmental conditions to molt and the best conditions to migrate.