Declining common toad body size correlated with climate warming

Accumulating evidence shows that the body size of organisms in many taxa is declining in response to global warming. We investigated the potential effect of rising temperatures on the body size of a common toad (Bufo bufo L.) population in southern England between 1983 and 2020. The body length (SVL; in millimetres) and body mass (in grams) of 15 550 males and 4004 females arriving at their breeding pond for the first time were recorded. Toad body condition was estimated using a scaled body mass index (SMI). Over the study period, the mean annual temperature increased by similar to 1.3 degrees C, whereas the mean SVL and SMI of both sexes declined. Multiple regression analysis showed that female and male SMI were negatively correlated with increases in mean summer temperatures, with females also being impacted minimally by mean winter rainfall. Mean body size (SVL) was positively correlated with toad abundance over the period between emergence as toadlets and arrival at the pond to breed for the first time. Common toads exhibited phenotypic plasticity in response to warming environmental conditions, resulting in a reduction in SMI and subsequent reductions in SVL and overall egg production, which occurred over a period of 10 years.