Releasing Stimuli for Antipredator Behaviour in the Common Toad Bufo B Ufo (L.)

RELEASING STIMULI FOR ANTIPREDATOR BEHAVIOUR IN THE COMMON TOAD BUFO B UFO (L.)

J.-P. EWERT 1) and R. TRAUD (Neuro-ethology and Biocybernetic Laboratories, University of Kassel, F.R.G.) (With 6 Figures) (Acc. 15-VII-1978)

INTRODUCTION

Toads are protected against predators by their poison skin glands. Little is known of their natural predators. Potential predators of the Common Toad Bufo bufo (L.) may live in different habits: (i) on the ground (hedgehogs, polecats, ringsnakes), (ii) in the air (owls, buzzards, the fly Lucilia bufonivora), (iii) in the water (leeches). From investigations of the stomachs of the owl Strix aluco (L.) we know (WENDLAND, T972) that around 5% of its vertebrate food is amphibia; com- prising 64,6% Pelobates fuscus (Laur.), 350?o Rana esculenta (L.) and Rana tem poraria (L.), and o,q.°,e Bufo bufo (L.) (see also UTTENDBRFER, 1952). One may conclude from this that owls avoid Common Toads as food. Another aerial predator is the buzzard Buteo buteo (L.); about 3% of its food is toads (MEBS, 1964; UTTFND6RFER, 1952). Buzzards eat the soft parts of the toad, but leave the skin. The fly Lucilia bufonivora (R. D.) is also an enemy of the toad. The larvae are parasitic in the toad's nasal cavity and damage parts of the forebrain. A terrestrial predator of the Common Toad is the hedgehog Erinaceus europaeus (L.) (GRZIMEK, ZIMMERMANN,1967). Hedgehogs do not avoid the toad skin. They even use toad venom for their own defence (BRODIE, 1977). It is also known that hedgehogs are tolerant to relatively high doses of the venom of common vipers. Polecats Putorius putorius (L.) prefer anurans but they seem to avoid toads (ZIMMERMANN,1967; HERTER, I95c?; GRZIMEK, In GRZIMEK (1971) the ringsnake Natrix natrix (L.) is named as the "arch-enemy" of the Common Toad. This snake has a special technique of prey capture in response to the toad swelling its body with air:

1) Supported by grants of the Deutsche Forschungsgemeinschaft Ew 7/6. 171

It seizes the toad and starting from one end squeezes the air out of its body (KLINGELHOFFER, i959). EIBL-EIBESFELDT (io6o) noted that potential aquatic predators may be leeches Haernopis sayagui.ruga (L.) which attach themselves to the skin of frogs (Rana temporaria L.), toads (Bufo bufo L.) and salamanders (Tri- turus alpestris Laur.). Young Hirudo medicinalis (L.) may attack anuran amphibians. The aim of the present investigation was (i) to study the behaviour of the Common Toad Bufo bufo (L.) in response to potential natural predators named above and (ii) to analyse appropriate enemy key stimuli in exper- iments using dummies.

Fig. i. Basic experimental procedure for measurements of the toad's avoidance activity in response to a predator dummy. The dummy stimulus (S), in this case a double stimulus configuration, was moved mechanically with a constant angular velocity around the toad which sat in the centre of a static circular arena (A). The stimulus holder (H) was mounted on a rotating disc (D) beneath the arena bottom (A). The arena was diffusely illuminated by a lamp (L) through a transparent cover (T).