Two amphibian species in the urban environment: changes in the occurrence, spawning phenology and adult condition of common and green toads

Abstract

Many features of the urban environment, such as a warmer microclimate, can positively affect populations of birds and mammals inhabiting cities, while at the same time may affect amphibians negatively. Also, amphibians from the temperate zone need both water bodies for reproduction and terrestrial habitats for foraging and hibernation, so changes in only one of these habitats may affect them negatively, and strong declines in many species are being observed. This study was conducted on two species, reacting differently to urbanization pressure – the common toad Bufo bufo and green toad Bufotes viridis. In the 1992–1994 breeding seasons, the occurrence of spawning toads in urban water bodies was established, and such a survey was repeated 15 years later (2007–2009). Over a shorter period, the breeding phenology, as well as the condition of breeding individuals, was studied. We found that after 15 years, a significant loss of the breeding sites of the two toad species took place, and the rate of their extinction was similar (39–47%), but green toad breeding ponds were located closer to the city center than before (2.4 vs 4.6 km). In both periods, the common toad spawned in water bodies located farther from the center (ca 7.2–8.7 km). The breeding phenology of both species was related to the minimal decade temperatures of April, and the green toad started to breed later than the common toad by 9–23 days. The condition of toad individuals differed between species, and after a colder winter, common toads were in better condition than green toads.