Impacts of climate and density on the duration of the tadpole stage of thecommon toad Bufo bufo

In an ongoing long-term study of a breeding population of common toads Bufo bufo at a pond in southern England, the dates of first spawning have been recorded since 1980, the dates of toadlet emergence since 1984, and the num bers of emergent toadlets estimated since 1988. The dates when spawn was fi rst laid varied considerably between years from the earliest: on 2 February 1993 (day 33) to the latest on 19 March 1996 (day 79). The duration of the tadpole stage was negatively correlated with the date of appearance of fir st spawn and was up to 30 days longer in early spawning years than in late ones. Despite this, toadlets still emerged from the natal pond up to 36 day s earlier in early spawning years than in late ones. Significant positive c orrelations were found between the duration of the tadpole stage and both t he proportion of days during the tadpole stage when the minimum ground temp erature was at or below 0 degrees C and the proportion of days when 10 mm o r more rain fell. Tadpole mortality was positively correlated with the prop ortion of days during the tadpole stage when the minimum ground temperature was at or below 1.5 degrees C. Evidence was also found to suggest that tad pole mortality was density-dependent, being proportionately higher when ini tial tadpole numbers were high than when they were low.