Eurasian ducks

Although best studied in North America, ringing has confirmed similar distributional patterns among ducks in Eurasia. In particular: (1) some species of ducks take up to 4-5 months over their post-breeding migration, the bulk of the population moving more rapidly or further in some years than in others; (2) individuals may winter in widely separated areas in different years; and (3) spring settling patterns may also vary from year to year. As in North America, all these features have been linked with patterns in water levels, freezing and thawing, all of which influence the distribution of habitat and associated food supplies. Thus, in Teal Anas crecca, spring settling patterns depended on conditions when the birds arrived: ring recoveries were concentrated to the south and west parts of the breeding range in wet, cool years, and to the north and east in dry, warm years (when wetlands were dryer than average) (M. A. Ogilvie, in Wernham et al. 2002). Depending on shallow waters, Teal are clearly sensitive to local conditions, whether drought, flood or freeze, which involves them at times either in

Figure 19.8 Recovery locations of Pochards Aythya ferina ringed in Britain in winter and found elsewhere in a later winter, showing that individuals can be found in widely separated areas in different winters. Only movements greater than 20 km are shown. There were 128 movements over 20 km, and another 29 under 20 km. From R. Hearn, in Wernham et al. (2002). Reproduced with permission of the British Trust for Ornithology.

Figure 19.8 Recovery locations of Pochards Aythya ferina ringed in Britain in winter and found elsewhere in a later winter, showing that individuals can be found in widely separated areas in different winters. Only movements greater than 20 km are shown. There were 128 movements over 20 km, and another 29 under 20 km. From R. Hearn, in Wernham et al. (2002). Reproduced with permission of the British Trust for Ornithology.

continual movement or alternatively in residency for weeks on end, all manifest on a continental scale. Individual Teal may be found in different winters in localities hundreds or thousands of kilometres (up to 3500 km) apart. The same holds for some diving ducks, with individual Common Pochards Aythya ferina, Tufted Ducks A. fuligula and others found up to several hundred kilometres apart in different winters (Figure 19.8; Wernham et al. 2002). In Common Pochard breeding dispersal distances of 200-600 km have been found, and in female Tufted Ducks up to 2500 km, but only a small proportion of females made such long moves (Blums et al. 2002).

In Europe, during hard winters many waterfowl appear in greater numbers than usual in milder southern and western parts of the continent. Ring recovery distances of several ducks (Eurasian Wigeon Anas penelope, Teal A. crecca, Northern Pintail A. acuta, Common Pochard A. ferina and Tufted Duck A. fuligula) were greater in cold winters than in mild ones, and greater in cold spells than in equivalent mild periods (Ridgill & Fox 1990). Other species showed no significant differences. Such hard weather (or 'escape') movements were associated with greater mortality than usual, but this may have resulted from greater vulnerability to hunting.

The number of waterfowl wintering near the northern limits of the wintering range depends on ice cover, which normally reaches its greatest extent in February-March. Many more birds stay in mild winters, with most open water, than in more severe ones (see Hario et al. 1993 for southwest Finland). The same is true for sea-ducks. In many regions, recent warmer winter temperatures have resulted in waterfowl wintering further north than previously (Chapter 21). Like other facultative migrants, food has a big influence on the winter distributions of ducks. Such species contrast with others which migrate well before food becomes scarce, at consistent times each year, as is typical of obligate migrants.

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