The back of the yellow-bellied toad (Bombina variegata) is brownish-grey and has small prominent warts and consequently animal is rough to the touch. It is characterized by a vibrant yellow colouration of the abdomen with a black-grey mottled pattern. The individual specimen of the yellow-bellied toad can be recognized by its characteristic pattern of abdominal spots, which is finally formed within two months after metamorphosis. They have a heart-shaped eye pupil, no external eardrum and parotid glands. They reproduce from late April to late summer. During mating, males float on the water surface and attract females by vocalizing. The male mating call is quieter than in fire-bellied toad because it has no internal vocal sacs. The frequency of calls (uuu – uuu – uuu) in yellow-bellied toad is 80 times per minute. The male mating calls are heard from the afternoon until midnight, at the peak of the mating season at the end of the spring, calls can be heard during the whole day. They only vocalize in clear weather without wind. During the mating season, mature males grow brown or black nuptial pads on the first two fingers and the inner surface of the forearms, helping them to better grip females during amplexus. The female may lay between 120-170 eggs in a season, which are attached to aquatic plants in small row-shaped clutches that contain about 15 eggs. Tadpoles are hatched from eggs within a few days and in about a month transformed into juvenile specimens and headed ashore.
The yellow-bellied toad is widely distributed in Europe, in large parts of Western, Central, Eastern and South-Eastern Europe. Eastern limit of its distribution is roughly the Carpathians. Yellow-bellied toads occur only in Slovenian project areas. Species is present all over Slovenia.
Adult specimens are most commonly found in temporary, sunny and disturbed habitats such as flooded wheel ruts, cattle troughs, mud puddles, ditches or quarries. Towards the south of Europe, their primary aquatic habitats are slow-flowing streams, shallow stream pools, smaller ponds, pools and puddles in swampy areas in hilly regions. They avoid water with fish. On the land, they find shelter in light forests along streams and marshy meadows, under dead wood, stones, between the roots of trees and bushes, where they also hibernate.
Populations of yellow-bellied toads are exposed to negative impacts due to the intensification of the use of forests and agricultural land and urbanization. The species is increasingly threatened by the disappearance of suitable terrestrial and aquatic habitats due to the drying up of floodplains, the regulation of watercourses, changing the water regime, backfilling of stagnant waters, introducing fish in aquatic habitats, environmental pollution and increased use of pesticides, herbicides and fertilizers in agriculture. Yellow-bellied toad metapopulation dynamic in Slovenian project areas is highly dependent on connectivity between surrounding terrestrial woodland habitats and ponds in the wetland. Main national roads in project areas are situated on the border between forest and wetland, which makes traffic road mortality a significant threat for them.
Interesting facts about fire-bellied and yellow-bellied toads
In areas where distributions of fire-bellied and yellow-bellied toads overlap, the two species successfully hybridize so that the entire contact area represents the so-called hybrid zone, where individuals with intermediate characteristics of both species can be found. Hybrids are usually morphologically similar to one of the parent species and are difficult to distinguish from the parent species by unprofessional. The whole Slovenian fire-bellied toad distribution range is in the hybrid zone.
Fire-bellied and yellow-bellied toads have poison glands in the warty skin. Potential predators are warned of their toxicity by the warning colouration on the belly, with the characteristic “unkenreflex” and playing dead. In danger, they throw themself on the back and show a mottled and vividly coloured belly to the predator. The anterior limbs are usually placed over the eyes and the posterior limbs are rigidly stretched upward. If the predator ignores the warning and the skin secretion comes in contact with their mucous tissue, it causes burning, tearing and sneezing, which is likely to be avoided at subsequent meetings.
Interestingly, adult specimens of both fire-bellied and yellow-bellied toads cannot stretch a tongue out of their mouth, so they don’t hunt flying insects. They rather pick up those that fall into the water or predate smaller insects and ground animals at night on land.