Population declines of Common Toads (Bufo bufo): the contribution of road traffic and monitoring value of casualty counts

Routine counts of Common Toads (Bufo bufo) killed by road traffic were used to demonstrate synchronous population declines since the late 1980s at three breeding sites in Cambridgeshire. All factors that might have contributed to the declines were considered in turn. It was concluded that road mortality of adult toads played a significant part at each site, although other factors were also implicated, especially habitat modifications. The level of local traffic flow was likely to have resulted in unsustainable losses, and counts decreased more rapidly on the busier roads. The use of counts of dead toads as a monitoring technique is discussed and suggestions made. A data-set of casualty counts needs careful interrogation, with analysis concentrating particularly on counts in the recent past. SINCE Blaustein & Wake (1990) drew attention to the decline of many amphibian species in different parts of the world, this subject has generated considerable debate and concern. In Britain, we have been aware of amphibian population decreases for rather longer, the Common Toad (Bufo bufo) being one of the species for which regional declines occurred in the first half of the twentieth century. Declines of the toad began during the early 1940s when the war effort demanded more effective agricultural operations, and populations suddenly decreased in intensively farmed areas such as the East Anglian Fens (Cooke & Ferguson, 1976). After the Second World War, agricultural intensification continued and this, together with loss of habitat in and around towns, led to widespread population declines of the toad in the 1950s and 1960s (Cooke, 1972). These decreases slowed in the 1970s, with the continual erosion of suitable habitat being partially offset by the creation of garden ponds, particularly in England (Cooke & Scorgie, 1983). However, in the 1980s there were signs of further declines in parts of central and southern England (Hilton-Brown & Oldham, 1991). By this time, conservationists were showing increasing interest in toads, in particular by attempting to reduce mortality by carrying toads across roads (Langton, 1989). In the mid 1990s, a survey of these volunteer patrols revealed that a high proportion believed their local toad populations to be declining (Foster, 1996). Following on from this observation, Carrier & Beebee (2003) undertook a postal enquiry and found for the period 1985-2000 that there had been significant declines in Common Toad populations in central, eastern and south eastern England. Underlying reasons for these population decreases were unclear, but they occurred for populations outside gardens and parks, and the Common Frog (Rana temporaria) remained relatively unaffected (Carrier & Beebee, 2003). This paper examines in detail one particular area in Cambridgeshire to determine whether recent declines occurred in Common Toad populations and, if they did, to attempt to unravel the factors responsible. While the situation may or may not be typical of those highlighted as of concern by Carrier & Beebee (2003), its recorded history up to 1980 broadly reflected that described Number 88 Herpetological Bulletin [2004] 13