EXTERNAL FACTORS ON THE SPAWN DATE 



131 



spawning, and not much in the previous week. At Valcntia, there was 

 no rain at spawning time, and only o-i mm four days earher. Valcntia 

 is a very wet place as a rule, so that the frogs were spawning in 

 abnormally dry weather for the district. 



Humidity 



Inspection of the charts for humidity is no more illuminating. Since 

 at night humidity is so often over 90 per cent, one cannot expect that 



RAIN 

 °C mm 

 12 5 



1930 



1931 



e 4 



-— -i-4^, 



6 12 



HOURS 



Fig. 34. The Weather at Eskdalemuir in 1930 and 193 1 for 

 24-hour periods 



Period extends from 18 hours on the night before spawn was recorded 

 (when it would probably be laid) and for the day itself, when it might 

 perhaps have been laid, up to 18 hrs. 1930 was wet, heavy rain falling from 

 01 hrs to HOG hrs. The temperature was fairly warm for Eskdalemuir, 

 which is high in the hills in South Scotland. In 193 1, there was a contrast. 

 No rain fell, and there was a frost all night from 21.00 hrs to 07.00 hrs. 



it would be critical for a nocturnal animal, which, when it was active, 

 would always fmd humidity near to the maximum possible. 



After these informal and cursory examinations of the data, the next 

 step is to see whether statistical examination supports the conclusions. 

 For temperature, there were no comphcations — no significant re- 

 lations were found, as can be seen in detail in the considerations set 

 out in Chapter 10, Appendix i h. 



There was a slight non-significant effect suggesting that, with far 

 more results, it might be possible to detect a tendency for more 

 spawning to take place when the maximum temperature was over 



