Monday, May 17, 2021

Amphibians As Indicators of the Environment

by Edin Sisson and Alaine Zhang 

Green frogs sound like a banjo
being plucked!

Avalonia Land Conservancy owns a large variety of wild habitats and local ecosystems and its mission is to steward and manage these habitats in a way that benefits both their ecological health and the  communities surrounding them.  In order to aid in these intentions, one crucial group of animals must be considered as both a concentration of care and a tool to gain insight on environmental health within Avalonia’s Preserves: Amphibians.  Frogs, toads and salamanders are complex organisms that are not only intriguing but are important to focus on when studying local ecology. During the past semester as students at Connecticut College, we partnered with Avalonia to help create awareness of amphibian life on our local preserved lands. In order to do this, we collected data weekly regarding the intensity of frog calls and wanted to create a blog post that reflects the significance of frogs within the areas studied. 


Vernal pond at White
Cedar Swamp
There are three main groups that Amphibians are categorized into; urodeles, anurans, and gymnophiones.  Urodeles are composed of newts and salamanders, anurans include frogs and toads all of which are vertebrates.  Gymnophiones are also vertebrates but have no limbs, and are otherwise known as caecilians. Amphibians are one of the oldest types of vertebrates and are distinctive because they live on both water and land at some point during their lives. Frogs and toads spend their early stages of development with gills, and then develop lungs and limbs to be able to survive on land as well. This unique development is what makes vernal pools, swamps, and shallow areas of ponds such great habitats for them to live. In addition to lacking hair and laying eggs, frogs and toads are exothermic, meaning their internal temperature is externally regulated by factors such as the sun. Frogs and toads are active during the spring and summer and hibernate during the rest of the year, usually in the mud of ponds. What we hear most frequently in the spring are the male mating calls, sung to attract females. The males fertilize the eggs after they are laid, during a process called external fertilization. In order to gain the upper hand over other males during mating season, they practice amplexus, in which they climb onto the female and wait for her eggs to be laid so that they can be the ones to fertilize them. Depending on the frog species, mating happens at different times during spring, the duration fluctuates as well depending on factors such as temperature and climate. There are some key differences between true frogs and true toads. True frogs are skinny with smooth, slimy skin and long legs. They leap and jump fairly long distances, and they have an upper jaw with small teeth. Frogs also lay eggs in large, often round, clusters. Toads, on the other hand, are generally warty and dry, live mostly on land, have fat bodies with short legs, and don’t hop that far. They also do not have teeth and lay their eggs in long strands rather than clumps. 


White Cedar Swamp is great habitat 
for frogs!

This spring we focused on frogs specifically, which can be hugely beneficial to us as humans, and to the ecological systems on Avalonia’s lands. They control insect populations as they are the main part of their diet, as well as providing food for predators such as fish, mammals, reptiles, and birds. With their skin and eggs being especially permeable, frogs are very sensitive to factors such as pollution, UV light, disease, and microscopic organisms. The pores on their skin allow them to absorb gasses like oxygen through their skin to breathe, but they also make the organisms prone to environmental changes in the water or air. When the pH of water or soil, for example, becomes too low and therefore acidic, materials such as heavy metal dissolve more easily, and therefore create toxins that are unhealthy for the local ecosystem. When exposed to these toxins, frogs are some of the first animals to die, or have mutations. Their small size also makes them susceptible to fatal environmental factors before larger animals like humans even become aware of the issue. There are many reasons for frog population decline including habitat loss, non-native species, climate disruption, parasites, and over-collection by humans. However, where  frogs are generally locally abundant, they are a great, accessible resource for scientists to use to study the changing environment. By recognizing fluctuations in frog populations and breeding time, we can observe what environmental issues might be problematic within our area here in Connecticut, and if possible, address them in productive manners. 


Pond at Pequotsepos Brook Preserve

While exploring both Avalonia’s Pequotsepos Brook Preserve and White Cedar Swamp, we heard three main species of frogs: The Spring Peeper (Pseudacris crucifer), the Green Frog, (Rana Clamitans), and the Pickerel Frog (Lithobates palustris). Spring Peepers are small frogs active from the end of the winter until the late fall and the most abundant frog species that we heard at our Avalonia sites. The Green Frog is a green or brown colored frog that feeds on insects as well as small amphibians. Green Frogs usually mate in April and early May but can continue into the summer months. Their call sound similar to the buckling of a banjo, which we heard during our final visits to White Cedar Swamp. Finally, we heard the Pickerel Frog at Pequotsepos Brook Preserve, which is a medium-sized frog with a lower-pitched call. It is also dark-colored somewhat rectangular dark spots and yellow or orange on the underside of its legs.

We performed research on the intensity of frog calls this spring under the protocols of the national Frog Watch USA organization. This organization calls upon trained volunteers all over the US to collect data on local populations of frog species and use it to monitor population decline, environmental changes, and potentially make positive steps to protect species countrywide. With the mission statement of Avalonia being to “[preserve] natural habitats in southeastern Connecticut by acquiring and protecting lands and by communicating the value of these irreplaceable resources,” these goals align extremely well, especially when applied to the conservation of the wetland habitats that Avalonia protects. By monitoring frogs on Avalonia’s lands, we can observe and analyze behavioral and population changes that could correlate with environmental concerns that negatively impact the ecosystems we cherish. 


Works Cited:


“Frogwatch Training Manual.” FrogWatch USA, 

Marshall, John. “Indicator Species: Using Frogs and Salamanders to Gauge Ecosystem Health.” GRIT: Rural American Know-How, 2021, 

Mosseso, John J. “Green Frog.” Connecticut Frogs and Toads, NBII, 

“Pickerel Frog.” Virginia Herpetological Society, Virginia Herpetological Society, 2021, 

Signs of the Seasons: A New England Phenology Program, The University of Maine Cooperative Extension, 




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