Green-winged Teal (Anas carolinensis) Science Article 4
The policy of the European Commission prohibits hunting of migratory birds while they travel to their breeding grounds. To date, spring migration dates of ducks have mainly been determined using bird counts, but the validity of this sometimes disputed method has never been tested. We used ring-recovery data from close to 9,000 teal Anas crecca ringed in the Camargue, southern France, to determine the onset of spring migration. This method makes it possible to avoid potential biases linked to duck counts, and was used to test the validity of spring migration dates inferred from such counts. Depending on the type of analysis (intra- or inter-annual recoveries), teal appeared to start migrating from the Camargue during the first or second 10-day period of January, with no significant differences between years, and no effect of the bird’s age or sex. However, when taking potential winter dispersion into account, we suggest that a conservative estimate for the onset of spring migration is the first 10-day period of February. Migration dates inferred from ring-recovery analyses were consistent with earlier results from duck counts, and provide a firm basis for policy making related to hunting. Though ringing data should be preferred when available, our study suggests that determining migration dates from bird counts may be a reliable method for teal, and potentially for other dabbling and diving ducks as well.
Matthieu Guillemain, Celine Arzel, Jean-Yves Mondain-Monval, Vincent Schricke, Alan R. Johnson & Geraldine Simon, Wildl. Biol. 12: 163-169