Flexibility of continental navigation and migration in European mallards

Abstract

The ontogeny of continent-wide navigation mechanisms of the individual organism, despite being crucial for the understanding of animal movement and migration, is still poorly understood. Several previous studies, mainly conducted on passerines, indicate that inexperienced, juvenile birds may not generally correct for displacement during fall migration. Waterbirds such as the mallard (Anas platyrhynchos, Linnaeus 1758) are more flexible in their migration behavior than most migratory songbirds, but previous experiments with waterbirds have not yet allowed clear conclusions about their navigation abilities. Here we tested whether immature mallard ducks correct for latitudinal displacement during fall migration within Europe. During two consecutive fall migration periods, we caught immature females on a stopover site in southeast Sweden, and translocated a group of them ca. 1,000 km to southern Germany. We followed the movements of the ducks via satellite GPS-tracking and observed their migration decisions during the fall and consecutive spring migration. The control animals released in Ottenby behaved as expected from banding recoveries: they continued migration during the winter and in spring returned to the population's breeding grounds in the Baltics and Northwest Russia. Contrary to the control animals, the translocated mallards did not continue migration and stayed at Lake Constance. In spring, three types of movement tactics could be observed: 61.5% of the ducks (16 of 26) stayed around Lake Constance, 27% (7 of 26) migrated in a northerly direction towards Sweden and 11.5% of the individuals (3 of 26) headed east for ca. 1,000 km and then north. We suggest that young female mallards flexibly adjust their migration tactics and develop a navigational map that allows them to return to their natal breeding area.

Figure 1. Recovery sites of banded mallards that were either ringed in Southern Germany or ringed abroad and recovered in Southern Germany.

Blue points are females, red points represent males. The banding data was collected by the ringing center Radolfzell, Germany, from 1947–2011.

Figure 2. Map of all tracked individuals.

Black lines indicate animals released in Ottenby (n = 14), grey lines represent animals translocated to and released at the Lake of Constance (n = 26). The release locations are highlighted by red circles.

Figure 3. Mean heading of winter migration for control birds in Ottenby (n = 4).

The distance traveled to the final wintering sites in indicated by the length of the bars.

Figure 4. Initial headings for spring migrations for both animals released in Ottenby (left panel, n = 4) and Radolfzell (right panel, n = 10).

The log(distance) traveled in this initial direction is represented by the length of the bars.