The reproductive success of the dipper Cinclus cinclus in relation to the acidity of streams in south-west Scotland

1. The breeding success of dippers Cinclus cinclus was assessed in south-west Scotland over 3 years and related to the acidity of the streams along which they bred. 2. At sites of high acidity, clutch and brood sizes were significantly smaller than those at sites of lower acidity. 3. Egg weight and the incidence of second clutches increased significantly with pH, but there was no evidence to suggest an effect of acidity on hatching success. 4. The rate at which food was delivered to individual nestlings was significantly lower at acidic than non-acidic sites. Nestling weights and survival were lower at more acidic sites. 5. Reduced brood sizes, low nestling survival and the low incidence of second brooding attempts resulted in a significant reduction in total productivity (number of fledglings produced, per pair, per year) at acidic compared with non-acidic streams. 6. It is suggested that pH-related differences in the invertebrate fauna of streams result in low prey availability for dippers on acidic streams, leading to reduced productivity.