POPULATION CHARACTERISTICS OF THE COMMON TOAD (BUFO BUFO) VISITING A BREEDING SITE IN MID-WALES

For 1978 the toad population migrating to the lake at Llandrindod Wells was estimated at 5700 males and 1950 females. The catchment area for toads was estimated as 340 ha, giving a density of twenty-three breeding toads ha-1 around the lake. The observed sex ratio of three males to one female is possibly explained by females breeding less frequently than males. (2) The number of toads moving was most strongly correlated with soil temperature, and toads did not move when the dusk air temperature was below 4 degrees C. The numbers moving each night increased throughout the migration, probably reflecting the increasing catchment area with distance from the lake. (3) Male toads arrived at the lake before females, and small males tended to arrive first. This probably overcomes competition for females from large males. Males marked at the beginning of the migration were recaptured throughout the collecting period, showing that after arriving at the lake some stayed for the entire migration. (4) Although breeding advantages increase with size, the size of toads is limited, probably by environmental factors. In relation to mate selection, female size is tied to male size but not vice versa. Both male and female length distributions are statistically normal. Weight and length are strongly correlated for males, gravid females and spent females.