Influence of weather conditions on pallid swift Apus pallidus breeding success

Abstract

The reproductive ecology of three colonies of pallid swift in a warm continental climate (Piedmont, NW‐Italy) was studied over a ten years period About 60% of the clutches were laid in late May and June, but continued until late August and September, when some females laid a second clutch Clutch size and the mean number of fledged young decreased progressively from spring to autumnLaying dates were influenced by rain and temperature unfavourable weather conditions during May induced most females to postpone egg laying until June Clutch size was not related to the rain or temperature parameters consideredThese observations differ from the findings about the common swift studied in cool temperate areas, where a very short stay in the breeding colonies does not allow a delay in laying, and spring weather conditions therefore have a strong influence on clutch size There are also differences about the effect of weather on chick rearing In warmer climates, typical of our colonies, fledging success is hindered both by too dry or too rainy seasons, even if these situations very rarely occur and the three‐egg clutch is always the most productive In colder climates the breeding success of the common swift depends primarily on the climatic conditions of May. and in bad weather a two‐egg clutch is more productive than a clutch of three In summary, the annual breeding success of the pallid swift appears little influenced by weather changes, due to a lesser impact of adverse conditions in Southern climates and the possibility, for this species, of shifting the laying period in response to a temporary worsening of climatic conditions