Geographical variability in, and temperature effects on, the phenology of Maniola jurtina and Pyronia tithonus (Lepidoptera, Satyrinae) in England and Wales

Abstract

ABSTRACT. 1. Geographical variability in, and temperature effects on, the mean date of adult flight period and the SD about this date are analysed for two univoltine, grassland butterflies in England and Wales from 1976 to 1985. Data were collected on the Butterfly Monitoring Scheme for Maniola jurtina (L.) at twenty‐nine sites and Pyronia tithonus (L.) at twenty sites.2. Substantial variability for mean date and SD occurs between years and between sites. Changes in mean date between years tend to occur consistently at different sites. The species show some parallel in variation between sites, especially for mean date.3. June maximum temperature accounts for 95% and 75% of the variation in mean date between years in M. jurtina and P. tithonus, respectively (r=‐0.97 and ‐0.87). Similar relationships occur for temperatures cumulated over the period of post‐winter development from March to July or August.4. Greater geographical variability in phenology, and a generally less synchronized flight period in M.jurtina may be associated with broader habitat preferences than in P. tithonus.5. The mean date of adult flight period remains at roughly the same date at more northerly latitudes. In M.jurtina the flight period becomes more synchronized, begins later and ends earlier in the north. P. tithonus shows little or no indication of such a response to latitude. This is discussed with regard to changes in season length and factors limiting the species’range.