Variability among autumn migration patterns of Mongolian Common Shelducks

Background

Avian migrants moving between common breeding and wintering areas may adopt different migration routes, and consequently affect timing. However, this pattern has rarely been investigated, especially in waterbirds. Moreover, autumn migration patterns of the Common Shelduck (Tadorna tadorna) have never been studied.

Methods

We used GPS transmitters to track, for the first time, the autumn migration of the Common Shelduck in East Asia (n = 14).

Results

The Common Shelduck undertook a broadly northwest–southeast autumn migration, taking a mean of 91.7 ± 38.7 (SD) days to cover a mean distance of 1712.9 ± 450.5 km at a speed of 89.4 ± 226.5 km/day. The birds used 2.5 ± 1.8 stopover sites, and the total stopover duration was 81.9 ± 38.7 days. There were considerable between-individual variations in the onset (24 August to 28 September) and completion (29 September to 11 January) of migration, distance (1070.2–2396.4 km), speed (14.7‒734.0 km/day), the index of straightness (0.6‒1.0), duration (1.5‒151.8 days), stopover times (0‒5) and total stopover durations (0‒148.1). More direct migration routes were associated with fewer and shorter stopovers (p = 0.003 in both cases). Post-breeding and wintering site habitat use was similar between individuals, whereas stopover site habitat use varied considerably within and between individuals.

Conclusions

Our study showed remarkable variability in Shelduck migration patterns, which was likely associated with refuelling patterns en route. To understand fully the migration diversity and flexibility of habitat-use, we need to track more birds to increase representativeness, using accelerometer-integrated transmitters to investigate behaviours in different habitats.