Costa Rican frog call study

Whilst on the University of Manchester field course in Costa Rica I conducted a project on frog calls, surveying the main swamp area that receives heavy rainfall almost all year round. I focused on the acoustic activity of the Red-eyed Leaf Frog, Agalychnis callidryas. In this post I present the most important conclusions from this study, as well as some interesting notes on the acoustic behavior of other pond breeding frogs.

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Study Site at La Selva (c) W.Chaves

One accurate way to interpret behavior in pond breeders is to analyze their acoustic activity along a shared area. My main focus was tracking the calling activity of male A. callidryas throughout the night, but the study also allowed me to identify 5 other species that might influence the species’ presence in certain areas of the pond.

After 3 nights of sampling, I concluded that the calling activity of A. callidryas was strongly diminished by the calls of the Hourglass Tree Frog, Dendropsophus ebraccatus, which is a little bit smaller than A. callidryas (Males about 23-27mm). This species was also the most widely distributed species along the study area, in contrast to others, such as Scinax eleaochroa, which presented a particularly high calling activity during the first night (it reduced for the remaining 2 nights).

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Hourglass Tree Frog, Dendropsophus ebraccatus (c) W.Chaves

The other three species (Tlalocohyla loquax, D. phlebodes, and A. saltator) presented a shy calling activity. However, the weather conditions could have influenced this as A. saltator is reported to be more active and even breed ‘en mass’ during heavy rainfalls. As for T. loquax and D. phlebodes, their low calling activity suggested no influence over the calls of the A. callidryas.

Since D. ebraccatus was the only species which proved to be affecting the calling activity of A. callidryas, I then decided to look more closely into this particular interspecific behaviour. While the A. callidryas males called in order to attract females to their higher perches, D. ebraccatus were usually found lower down, near shallow water where sedges or semiaquatic plants dominated. Although males of A. callidryas were also seen calling from low perches, there were few if any suitable leaves for this species to lay its egg masses on there. The calling of A. callidryas from low perches may also have been affected by neighbouring frogs at this level as these would cause a high level of acoustic interference.

 Almost at midnight, the calls of A. callidryas diminished along with the calling activity of all other hylid species found at the swamp. This group response could be interpreted as an anti-predatory strategy to decrease the risk of predation from bats. However, to hear the frog calls I was working with here is a sound recording I made that includes the species mentioned:  
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Male Red-eyed Tree Frog, Agalychnis callidryas, at the study site. (c) W. Chaves

Conducting projects that investigate specific animal behaviours, such as the one which focuses on the calling activity of A. callidryas, are of growing importance. When considering future studies on the ecology, bio-acoustics, and the different aspects of reproduction in this species, an extension of this project’s methodology may be useful. I intend to develop it in future assessments of populations of this species along its Atlantic distribution.

I hope to share some more information on frogs of the Neotropics in further posts, but would like to encourage visitors to comment on my work  –  or if you have any suggestions or ideas for the project`s improvement or other future science projects please post a comment, I would love to hear from you. Many thanks, Wagner.

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