Dipper © Richard Steel
Most Dippers are sedentary but this Atlas shows clear evidence of altitudinal migration, with some birds descending to lower altitudes in winter. The map illustrating the difference between breeding and wintering distribution shows clearly that most of the nine tetrads occupied in winter but with no breeding season record are to the west, at lower altitude than their breeding range. Omitting the bird holding a territory spanning SJ75T and U, four of the five tetrads occupied in the breeding season only, with no winter record, were above 300 m, while seven of the eight tetrads occupied in winter only, with no breeding season record, were below 200 m, four of them below 100 m. Some of the highest altitude territories, such as in SJ96Y, SJ96Z and SJ97V, had birds present in both seasons, however, so some birds are able to survive winters in upland Cheshire. Perhaps some of those at lower altitudes are first-year birds that have been driven out by their parents. Coward, who in his 1910 book described the Dipper as ‘an abundant resident on the hill streams in the east’, noted that ‘many of the birds leave the high ground in the late summer or autumn, and in winter the Dipper is occasionally met with on the lower reaches of the larger streams and on brooks in the plain’.
Mid-stream stones covered with droppings often indicate Dippers’ favoured sites. Many birds maintain winter territories, usually as pairs and often coinciding with their breeding territory, provided that they can provide sufficient of their winter diet, caddis and dipteran flies, shrimps, fish and molluscs. Many of the aquatic invertebrates reach their peak populations during winter, prior to spring emergence, and the upland watercourses seldom freeze so food availability should not be a problem. Dippers often sleep overnight in communal roosts, mostly of two birds but sometimes more, in nooks and crannies under bridges where they can stay warmer on cold, windy nights.
Even in midwinter, residents sing strongly to re-establish their territories and anticipate the breeding season. Apart from the portion of the population that undertakes altitudinal migration, there is remarkably little seasonal difference in the Dippers’ lives. This is such an important indicator of the state of our upland watercourses that it deserves monitoring closely.
Sponsored by N. and K. Parry
