Spawn site selection and colony size of the frog (Rana temporaria) and the toad (Bufo bufo)

Information has been collected from various sources on spawn site selection and colony size of the frog ( Rana temporaria ) and the toad ( Bufo bufo ). Details are tabulated for 764 frog breeding sites in Britain and in the Republic of Ireland and for 139 toad sites in Britain (the toad does not occur in Ireland). Both species tend to breed in whatever types of site are most available. In Britain the garden pond has steadily increased in importance for both species since 1950. Frogs usually spawned in shallow water, 266 reports out of a total of 588 (45%) referring to water up to six inches (15 cm) deep. Toads tended to spawn in deeper water, 48 reports out of 82 (59%) mentioning water 7–18 inches (18–46 cm) in depth. Median depths were: frog, seven inches (18 cm); toad 13 inches (33 cm). Information on colony size was assimilated for 574 frog colonies and 86 toad colonies. Colonies in gardens were smaller than those in other types of site. Relatively fewer large frog colonies (≡100 animals) were found to occur in London than elsewhere in Britain, and British colonies were generally larger than those in Ireland. Colonies of 100 or more individuals were recorded relatively more frequently for toads than for frogs. By combining information on choice of site and colony size, rough estimates can be derived of the percentage of frogs and toads breeding in gardens and other types of site. For instance, in the London area in the 1960s perhaps 20–25% of the frogs bred in gardens and private grounds. The ecological significance of these observations is discussed.