Movements, home-range size and habitat selection of mallards during autumn migration

Abstract

The mallard (Anas platyrhynchos) is a focal species in game management, epidemiology and ornithology, but comparably little research has focused on the ecology of the migration seasons. We studied habitat use, time-budgets, home-range sizes, habitat selection, and movements based on spatial data collected with GPS devices attached to wild mallards trapped at an autumn stopover site in the Northwest European flyway. Sixteen individuals (13 males, 3 females) were followed for 15-38 days in October to December 2010. Forty-nine percent (SD = 8.4%) of the ducks' total time, and 85% of the day-time (SD = 28.3%), was spent at sheltered reefs and bays on the coast. Two ducks used ponds, rather than coast, as day-roosts instead. Mallards spent most of the night (76% of total time, SD = 15.8%) on wetlands, mainly on alvar steppe, or in various flooded areas (e.g. coastal meadows). Crop fields with maize were also selectively utilized. Movements between roosting and foraging areas mainly took place at dawn and dusk, and the home-ranges observed in our study are among the largest ever documented for mallards (mean = 6,859 ha; SD = 5,872 ha). This study provides insights into relatively unknown aspects of mallard ecology. The fact that autumn-staging migratory mallards have a well-developed diel activity pattern tightly linked to the use of specific habitats has implications for wetland management, hunting and conservation, as well as for the epidemiology of diseases shared between wildlife and domestic animals.

Figure 1. Spatial distribution of mallard GPS fixes (white dots, all individuals pooled) on southern Öland, Sweden, October – December 2010.

Fixes from flying birds (speed >4 m/s) are excluded.

Figure 2. Example of typical mallard movements between frequently used sites on southeast Öland, Sweden, October – December 2010.

A (no. 1463): Orange ovals  =  coastal meadows; yellow ovals  =  maize fields; red ovals  =  flooded areas; blue ovals  =  coastal day-roosts (the upper is a sheltered bay, the lower is open water); green ovals  =  coastal reefs used as day-roosts; grey circle  =  duck trap location. B (no. 1426): Yellow oval (1)  =  maize field visited during dawn and dusk; red ovals (2)  =  various small (flooded) wetlands on alvar steppe (the upper one reaching into a maize field), visited at night; green oval (3)  =  coastal reef used as day-roost. C (no. 1440): Yellow oval (1)  =  two maize fields frequently visited, mostly during dawn and dusk; red oval (2)  =  flooded area (stream) visited most nights; light purple oval (3)  =  flooded pasture visited during two consecutive nights (probably for feeding); blue oval (4)  =  most frequented day-roost.

Figure 3. Percentage of time spent by mallards in different habitats (all individuals, with standard deviation bars) on southern Öland, Sweden, October – December 2010.

Figure 4. Home-range size (MCP in ha on a log scale) of mallards on southern Öland, Sweden, October – December 2010, during different periods of the day; dawn  =  first light to sunrise (duration close to two hours), day  =  sunrise to sunset (7–9 hours), dusk  =  sunset to last light (duration close to two hours), and night  =  last light to first light (11–13 hours).

Figure 5. Distance between consecutive locations for 16 mallards on southern Öland, Sweden, October – December 2010, during different periods of the day; dawn  =  first light to sunrise (close to two hours duration), day  =  sunrise to sunset (7–9 hours), dusk  =  sunset to last light (close to two hours duration), and night  =  last light to first light (11–13 hours).

Figure 6. Manly et al.'s selection ratios (w_ij±95% CI) for each period of the day.

Habitat is considered as a six level factor, i.e. all wetland habitats have been pooled.