EXTERNAL FACTORS ON THE SPAWN DATE I23 



The Effect of the Weather at the Time of Spawning 



During many walks over the fields, I became increasingly sceptical 

 about the significance of any effect of the weather at the time of 

 spawning. There were too many instances of frogs spawning in cold 

 weather, and too many when they did not spawn when it was warm, 

 and too many similar ponds in wliich, although they were near to- 

 gether, the frogs spawned at different dates. In order to provide 

 sufficient data for statistical analysis by my own efforts, I should have 

 had to observe for a very long time, and confirmation of my sus- 

 picions had to be deferred until I could analyse the Phenological data. 

 It is perhaps important to point out that the doubts arose literally in 

 the field — they were not the result of examining data. 



The map, Fig. 28, should now be studied. In Phenological hterature 

 dates are counted from January ist which is Day i. February ist is 

 therefore Day 32, and so on. 



The earhest areas for spawning, with dates in January, occur only in 

 two places : in the Dartmoor and Exmoor areas of Devonsliire, with 

 an extension into South Wales on the other side of the Bristol Channel, 

 and in the South West of Ireland. Cornwall is slightly later, and has 

 similar dates to the West of Wales, and the areas to the North of the 

 earhest areas. An observer at Campbelltown, in the Kintyre Peninsula 

 of Scotland recorded six successive early dates. Next in order are areas 

 on the West coast of Lancashire, much of Southern Ireland, an area in 

 Wales, and parts of Dorset. The West Midlands, South West England, 

 a strip along the South-East coast of England, and an area over the 

 Yorkshire Wolds and Moors, a small patch North of the Cheviot 

 Hills, West Scotland as far as known, and North Ireland form fairly 

 early spawning areas. The 70-day isophene (line of equal date) 

 encloses a very large area, from almost the extreme South-East of 

 England to the North of Scotland, with patches in North Ireland, as 

 far as known. Late spawning areas, enclosed by the 80-day isophene, 

 are: the Eastern Counties of England, the industrial areas, a patch 

 in South-East Scotland, and two interesting patches to the south of 

 both the Firths of Forth and Moray in Scotland. With the exception 

 of an interpolated ring round the latest area of all, the 90-day isophene 

 only appears in industrial Yorkshire. The black patch in North- West 

 England deserves special attention. It is an area near Crossfell in the 

 Pennine mountains. There the mean date is over 100. 



This map can be easily interpreted in the hght of the facts discovered 



