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Reddish Vale Country Park

Unlike many water birds, dippers are generally similar in form to many terrestrial birds (for example they do not have webbed feet), but they do have some morphological and physiological adaptations to their aquatic habits.

 

Their wings are relatively short but strongly muscled, enabling them to be used as flippers underwater. They have dense plumage with a large preen gland for waterproofing their feathers. Their eyes have well-developed focus muscles that can change the curvature of the lens to enhance underwater vision. They have nasal flaps to prevent water entering their nostrils. Their blood has a high haemoglobin concentration, allowing a greater capacity to store oxygen than terrestrial birds, and allowing them to remain underwater for up to at least 30 seconds.

 

Dippers have declined in west Wales, south-west and north-east England and various parts of Scotland since 1970, while the population has remained stable elsewhere. Acidification of streams, caused mainly by airborne pollutants creating acid rain, in these parts of the country appears to be the primary reason for this. Coniferous trees close to streams and in catchment areas can exacerbate this, since they trap acidic pollutants on their foliage, and consequently have more acidic water draining from them. The acidification reduces the abundance of aquatic invertebrate prey and may also cause calcium deficiency in egg-laying females resulting in thinning of eggshells.

 

In central Europe declines in dipper numbers arise as a direct result of industrial pollution, while hydroelectric and irrigation schemes that reduce flow rates in otherwise suitable watercourses are the most likely reasons for decline in the southern Europe.

 

Dippers forage for small animal prey in and along the margins of fast-flowing freshwater streams and rivers. They perch on rocks and feed at the edge of the water, but they often also grip the rocks firmly and walk down them beneath the water until partly or wholly submerged. They then search underwater for prey between and beneath stones and debris; they can also swim with their wings. Their prey consists primarily of invertebrates such as the nymphs or larvae of mayflies, blackflies, stoneflies and caddisflies, as well as small fish and fish eggs. Molluscs and crustaceans are also consumed, especially in winter when insect larvae are less available.

Dipper

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Length 18cm

Wingspan 28cm

Weight 64g

Diet, large invertabrates,

especially caddisflies,

Maximum recorded age

8yrs 4months, typical age 3years.

Dipper