Abstract
Relationships are examined between laying dates of aerial insectivore Little Swifts Apus affinis and weather conditions during the pre-laying periods from 1986 to 1989 at a colony in central Japan. The breeding season was remarkably long, with first eggs laid in mid-April and last chicks fledged in ealry December. Almost all pairs annually fledged two or more broods. Mean laying dates for first clutches varied significantly among years. Temperatures during about one month before laying were important to mean laying dates of first clutches. Mean laying dates for both second and third clutches also varied significantly between years. However the mean laying dates had no significant relationship to weather conditions before laying. It is likely that the correlation between egg laying for successive clutches led to the significant yearly differences of mean laying dates for second and third clutches. Female age also affected laying dates. Females of three years old or more (≥3-yr) highly significantly laid eggs earlier than two-years-old (2-yr) females for all the three clutches. The number of clutches that female produced annually varied significantly between years. Individual females that bred earlier had more clutches than those that bred later. Females of ≥3-yr had more clutches than 2-yr females, because ≥3-yr females laid eggs earlier than 2-yr females.
