The distribution of dippers,Cinclus cinclus(L.), in the acid‐sensitive region of Wales 1984–95

Abstract

1. Dippers were surveyed along seventy‐four acid‐sensitive streams in upland Wales in 1984 and again in 1995. At forty‐eight of the sites, and in an additional twenty‐three to twenty‐nine adjacent catchments, changes in acid‐base status and macroinvertebrate communities were assessed. River habitat surveys (RHS) and GIS (Geographical Information System) provided information on habitat features. 2. pH means across all the sites were higher on average by 0.12 pH units in 1995 than 1984, accompanied by significantly increased total hardness and reduced sulphate. However, geometric mean aluminium concentrations increased significantly, while the abundances of important dipper prey either remained constant (Ephemeroptera) or declined (Trichoptera; Plecoptera). 3. As in 1984, dipper distribution in 1995 was related to acid‐base status: aluminium concentrations were significantly higher, and pH significantly lower, at sites where dippers were absent. In both surveys, there were significantly more bankside broadleaves and fewer conifers where dippers were present. 4. Although dippers occurred in 1995 on a similar number of streams as in 1984, there were both gains and losses, and an overall significant reduction in the number of visits on which birds were recorded (= registrations) per survey reach. Gains and losses were not related to habitat structure or acid‐base status, and might be stochastic. Mean aluminium concentrations increased more (P < 0.06) at sites where dipper registrations fell, than where they increased, but changes were large enough to explain altered occupancy at only five sites. Plecopteran abundances declined most at sites losing birds. 5. We conclude that recovery from acidification has not yet been large or sustained enough to allow widescale increase in the Welsh dipper population, and continued decline cannot be excluded. There is a need for better understanding of how recovery processes will permeate foodwebs to reach top predators in acidified streams, and of the geographical scale of recovery required to increase populations in dispersed organisms such as birds. Such uncertainties, together with the mismatch in trends revealed by stream chemistry and dippers, illustrate reasons why chemical data alone are inadequate for the assessment of changing river quality.

Plecoptera response to acidification in several headwater streams in the Vosges Mountains (northeastern France)

“…Numerous studies have revealed strong effects of acidification on most biotic compartments of freshwater ecosystems, from planktonic organisms (Almer et al 1974;Harvey et al 1981;Havens 1991), macrophytes (Grahn 1986), fish (Leivestad and Muniz 1976), amphibia (Horne and Dunson 1995), birds (Scheuhammer 1991;Buckton et al 1998) and even mammals (Glooschenko et al 1988;Mason and Macdonald 1989). More particularly, many researchers have focused on the effects of acidification on the composition and structure of macroinvertebrate communities (Sutcliffe and Carrick 1973;Hall et al 1980;Harriman and Morrison 1982;Sutcliffe and Hildrew 1989;Feldman and Connor 1992;Gue´rold et al 2000).…”

Seasonality, water quality trends and biological responses in four streams in the Cairngorm Mountains, Scotland

“…The biological responses to chemical change have also been investigated across a range of spatial and temporal scales, and with respect to different groups of organisms (Battarbee et al, 1988;Edwards et al, 1991;Juggins et al, 1996;Lancaster et al, 1996;Buckton et al, 1998). Disentangling the effects of long-term and short-term changes at different spatial scales, however, has proved extremely difficult (Ormerod and Jenkins, 1994).…”

Calculating census efficiency for river birds: a case study with the White‐throated Dipper Cinclus cinclus in the Pyrénées

“…Detailed territory mapping combined with general use of the binomial model is a sensitive tool for environmental managers or scientists and may serve different objectives: (i) simple assessment of population size, (ii) long‐term assessment of variations in annual size of the population, or general trends (Marchant & Hyde 1980, Saether et al . 2000) or (iii) modelling of bird abundance in relation to habitat quality (Rushton et al . 1994, Buckton et al .…”

“…Among them, the White‐throated Dipper Cinclus cinclus (hereafter: Dipper) is one of the most widely studied, especially in Europe (Spitznagel 1985, Tyler & Ormerod 1994). This species has proved valuable for assessing responses to acidification (Buckton et al . 1998) and river regulation (D’Amico et al .…”