Into thin air: vertical migration, body condition, and quality of terrestrial habitats of alpine common toads, Bufo bufo

Abstract

Since the end of the 1980s there has been increasing evidence of worldwide amphibian declines in high-altitude regions. Moreover, amphibian conservation has so far mostly neglected the terrestrial habitat, which is essential for effective protection measures. We determined the location and quality of terrestrial habitats of common toads (Bufo bufo L., 1758) in a naturally fragmented alpine environment (Schlumsee, 1105 m a.s.l., Northern Calcareous Alps, Austria) characterized by a high diversity of available microhabitats. By radio-tracking 18 individuals during their post-spawning migration, we located terrestrial habitats 130–1000 m horizontally away from and 85–390 m above the breeding site. This is the first study to show vertical migration over several hundred metres in adult amphibians. Both adult and juvenile toads completed the migration within 2–7 weeks and, on their way to the summer habitat, climbed 45° scree slopes and ascended cliffs with slopes of up to 65°. Body condition indices were highest for individuals originating from the terrestrial summer habitat at the highest elevation, which is characterized by the highest vegetation diversity, a high abundance of food, and the highest insolation, probably allowing the toads to extend their activity period for food intake. Our study suggests that under demanding climatic conditions it can pay off for toads to undertake costly migrations to reach high-quality habitats. For amphibian conservation, high-value habitat patches need to be located and investigated to increase the effectiveness of protection measures.