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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.

Frogs and Physics!

Over the past couple of days we have been running our new A-level study days in conjunction with Dr Mark Dickinson of the Photon Science Institute. The talks and interactive practical sessions are aimed at providing sixth form students with first-hand experience of science in action, and more specifically to help them understand how we are applying some cool innovative techniques to investigate the optical and structural properties of amphibian skin. Students from Whalley Range High School for Girls,Verdin High School, Macclesfield, and Ashton Sixth Form College all visited the museum and got to grips with a wide range of kit which allowed them to investigate for themselves the frogs’ thermoregulation and Infra-red reflecting pigments. 

Following the morning sessions in the Museum, where the pupils got to learn about the frogs and had an introduction to the physics. The afternoon was spent in Mark’s Lab where the pupils used Hi-tech spectrometers, Infra-red cameras, thermal imaging and Optical Coherence Tomography equipment (OCT). OCT is a remarkable new technique being developed at Manchester that allows us to see whats going on below the skin’s surface through producing a series of 3D images using light (see clip below for an OCT image of skin on a human palm (note the spiral sweat gland). We hope everyone from the schools enjoyed their visit and would like to say a big thanks to all the demonstrators who helped us deliver the sessions.  

                   (Image above courtesy of Mark Pierce, Wellman Labs)

Ifra-red reflectance research at Manchester and in Costa Rica:

Andrew shows OCT equipment at Manchester: http://news.bbc.co.uk/1/hi/sci/tech/7464437.stm  

Mark tests rare frog skin with a spectrometer in Costa Rica: http://news.bbc.co.uk/1/hi/sci/tech/7603225.stm

Link to The Photon Science Institute : http://www.psi.manchester.ac.uk/

Rare frog found!

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(c) Andrew Gray, 1997

Andrew and the team of researchers on the Costa Rican expedition have found the rare and critically endangered Red-eyed stream frog Duellmanohyla uranochroa. The BBC following the group have been able to film this species for the very first time! For more on this story see the link below.

http://news.bbc.co.uk/1/hi/sci/tech/7603295.stm

Sunbathing aids frogs in cure for deadly fungus?

Rather than taking frogs from the wild, Andrew and Mark take hi-tech equipment to the rainforests of Costa Rica!

Rather than taking frogs from the wild, Andrew and Mark take hi-tech equipment to the rainforests of Costa Rica!

Follow this link to see Andrew explaining about some of the important Infra-red reflectance research he is doing in collaboration with Mark Dickinson and Richard Preziosi at the University of Manchester : http://news.bbc.co.uk/1/hi/sci/tech/7464437.stm

For his other research work using OCT, see also: http://www.octnews.org/entity/profile/andrew-gray/