Aspects of the breeding ecology of Welsh Grey WagtailsMotacilla cinerea

We studied the abundance, reproductive performance and diet of breeding Grey Wagtails on rivers in mid and south Wales between 1978 and 1985. Breeding abundances ranged from 0 to 15 pairs per 10 km. Birds were commonest on hard water streams with abundant aquatic invertebrates and they appeared to favour streams lined by deciduous trees. Most females probably started to lay in April but replacement and subsequent clutches extended the breeding season into July. Median laying dates varied annually and were correlated with the mean air temperature in March. Pairs at altitudes over 300 m bred significantly later than those at lower altitudes. Fifty-two per cent of nesting attempts produced fledged young. The mean size of 147 clutches was 5.07. Clutches started in May were significantly larger than those started in April or June. We suggest that the increased reproductive effort coincides with an increase in breeding success. Adults and nestlings had similar diets in terms of insect orders: Trichoptera, Ephemeroptera and Plecoptera each provided 10-20% of the items taken and adult Diptera about 55%; aquatic insects formed 25% of the diet.