Written by Dr. Laurence Jarvis (external contributor)
Anurans (frogs and toads) are well known for their vocal abilities, particularly during the breeding season. However, visual cues are less studied and understood. Toe tapping is an unusual and interesting behaviour exhibited by a range of amphibian species. Also known as toe twitching, wiggling or trembling amphibians will typically raise or wave one or more legs or feet in the air. This may be slow or very fast. The behaviour appears to be performed by a range of amphibian species as a recent study found reports of toe tapping from 42 amphibian species from 12 families1. There is currently no consensus on the exact reason for toe tapping that can be applied to all amphibian species. The behaviour often appears to occur in response to the presence of prey and may be linked to prey capture. It has also been noted to occur in relation to mate attraction and courtship, such as in the Southern Hispaniola Crested Toad (Peltophryne guentheri), as well as aggression. However, toe tapping may vary widely within a species with individuals sometimes performing the behaviour and not at other times2. When the movements are slow with a raised limb, this is referred to as pedal luring and this is thought to attract prey through mimicking vibrations produced by the prey, as observed in the South American horned frogs (Ceratophrys spp.). However, Sloggett & Zeilstra (2008) proposed that instead, toe-tapping may cause additional vibrations that keeps the prey moving in order to allow detection by the frog3. In support of this hypothesis, a recent study of poison dart frogs (Dendrobatidae) found that individual frogs increased their toe tapping behaviour when prey were inactive which resulted in increased prey movements and more effective detection2.
Dyeing poison frogs (Dendrobates tinctorius) of South America have often been observed to tap their posterior toes4. This tapping can be incredibly rapid with reports of up to 500 taps per minute, which is near the limit of vertebrate muscular vibration4. Adults of this species feed on a range of small and fast-moving prey such as flies and other arthropods so effective prey capture is essential. Research carried out by Parrish and Fischer (2024), found that frogs performed toe tapping more whilst feeding and when on a surface that would carry the vibrations, such as smooth leaves4. The frogs performed toe tapping much less when sitting on soil which transmit vibrations more slowly. The researchers also found that individuals increased their toe-tapping whilst in the presence of a breeding partner. The reasons for this are unclear but shows that this species may adapt its tapping behaviour depending on the presence of other individuals, particularly breeding partners. Overall, this study supports the work of Sloggett and Zeilstra (2008) and suggests that toe tapping may agitate small arthropods by substrate vibrations and thereby help the individuals to detect their prey4.
The Yellow-striped Poison Frog (D. truncatus) is a poison dart frog native to Colombia. In an attempt to further understand the function of toe tapping in this species Vergara-Herrera et al. (2023) designed an experiment to examine the vibrations produced during toe tapping5. The results confirmed that toe tapping was performed in relation to prey capture. In addition, the researchers found that tapping rate accelerated during their sequence of attacks on prey during foraging5. This is analogous to the foraging behaviour of species including bats, dolphins and sperm whales, all of which increase call rate as they approach their prey. In these species it is thought that the increase in call rate immediately prior to capturing their prey helps to confirm its location, speed and movement and thus aid in capture. It is not known whether this is the reason for increasing tapping rate in the Yellow-striped Poison Frog but the acceleration is likely to aid in final prey capture. If the toe tapping serves to further agitate the prey, as proposed by Sloggett & Zeilstra (2008), then more rapid toe tapping would make the prey more detectable, and thus easier to capture by the frogs.
Toe tapping is an under recorded behaviour but is being noted in an increasing number of species worldwide. The genus Pseudophryne consists of 14 endemic Australian species, all of which are small, cryptic ground-dwelling species. Toe tapping has only previously been recorded in one other species within the genus6. The Southern Corroboree Frog (Pseudophryne corroboree) is a critically endangered species, restricted to areas above 1300 m elevation in New South Wales, Australia. Recently it was not thought to exhibit toe tapping behaviour. However, during captive breeding, McFadden et al. (2008) observed rapid toe tapping prior to being fed crickets6. In this species, for the vast majority of individuals, the tapping foot was raised off the substrate and waved as in the South American horned frogs. This is in contrast to poison frogs, which usually tap their feet whilst in contact with the substrate. The behaviour of the Southern Corroboree Frog would suggest that the moving foot is used to attract prey, rather than trigger movement. Alternatively, as stated by the researchers of the study, it is possible that the tapping could be simply an excited response to the presence of prey.
Overall, toe tapping is an interesting behaviour which has been observed in a wide range of amphibian species. Increased observations and studies on a wider range of species are demonstrating that the behaviour is more widespread than previously thought. Although the exact functional significance is not always fully understood, and may vary between species, it demonstrates the capacity for varied visual cues to be utilised by frog and toad species.
References
1Erdmann J.A. (2017). The function of toe movement in feeding by the gulf coast toad (Incilius nebulifer). Masters thesis, Southeastern Louisiana University.
2Claessens L.S.A., Ganchev N.O., Kukk M.M., Schutte C.J., and Sloggett J.J. (2020). An investigation of toe-tapping behaviour in anurans by analysis of online video resources. Journal of Zoology, 312 (3): 158–162. https://doi.org/10.1111/jzo.12815.
3Sloggett J.J. and Zeilstra I. (2008). Waving or tapping? Vibrational stimuli and the general function of toe twitching in frogs and toads (Amphibia: Anura). Animal Behaviour, 5: e1–e4.
4Parrish T.Q. and Fischer E.K. (2024). Tap dancing frogs: Posterior toe tapping and feeding in Dendrobates tinctorius. Ethology, p.e13465.
5Vergara-Herrera N., Cocroft R. and Rueda-Solano L.A. (2023). Eating to the beat of the drum: vibrational parameters of toe tapping behavior in Dendrobates truncatus (Anura: Dendrobatidae). Evolutionary Ecology, 1-17. https://doi.org/10.1007/s10682-023-10277-x
6McFadden M., Harlow P.S, Kozlowski S. and Purcell D. (2010). Toe-twitching during feeding in the Australian myobatrachid frog, Pseudophryne corroboree. Herpetological Review, 41(2): 153-154.