Nest Records of the Swallow

The laying period of the Swallow (Hirundo rustica) in Great Britain ex- tends from the end of April to the end of August with a large peak between 13 May and 16 June and a smaller one between I and 21 July.The main start of laying is about a week later in the north of England than in the south.2. From records so far accumulated the average clutch size is 4.4 eggs, starting at 4.7 eggs at the end of April and declining to 3.8 in August.3. The average incubation period is 15.3 days ; the nestling period 19.1 days.4. The breeding success was higher than in most species previously studied from the Nest Record Cards.