What is Killing Frogs?

I’ve been interested in conservation for a long time, through my schooling and my Master Hereptology certificate.

Whenever I visit a zoo I see the population projects they are working on, and a handful of them involve amphibians.

There is a global amphibian decline occurring right now caused by many different factors. 

Deforestation due to urbanization, disease-causing fungus, anthropogenic pollution, and climate change are known to be the main causes of frog deaths worldwide.  

Starting in the 1950s scientists started to notice a decline in amphibian populations around the world. 

The thing is, we are unable to nail down one specific cause for frog deaths across the world.

There are several factors that contribute to declining amphibian populations in different countries and continents.

Some factors, like deforestation, climate change, and the pet trade, can all be reasons why a specific population is declining.

Pollution is Killing Frogs

When I think of frogs I think of water and frogs as bioindicators.

When I think of pollution and frogs I think of water pollution.

Yes, this is a major cause of frog decline, but pollutants in the water are not the only factor contributing to amphibian decline. 

A pollutant is a harmful substance that becomes introduced into an environment it was not in previously. 

Since frogs lay their eggs in water, egg development in aquatic breeding grounds is hindered by water pollution.

Unhealthy Wood Frog eggs I found in a polluted freshwater system

Water pollution is seen as elevated nitrate levels mainly caused by agricultural runoff from fertilizers. Breeding grounds become acidic and oxygen levels waiver, decreasing egg survivability. 

Adult frogs can be affected by pollution due to their porous skin.

Frogs breathe  and respire through their skin, so any pollution on their skin can disrupt that process.

A frog hopping or digging through agricultural fields or home gardens where pesticides are used can harm their skin. 

Chytrid Fungus is Killing Frogs

Chytrid Fungus is a contributor to the current global amphibian decline. This is a disease-causing fungus that rapidly kills affected frogs. It has spread worldwide from its first known case in the late 1930s. 

The origin of this fungus is a little shaky, Weldon et. al, (2004) suspect it to have originated in Africa and spread across the world through trading of African clawed frogs for pets.

Since 1938, it has been found globally in almost every continent that contains amphibian species.

African clawed frogs are likely a carrier of the disease since it does not affect them as it does other species. 

Frogs infected with Chytrid Fungus display chytridiomycosis. 

Chytrid fungus causes, sound it out with me, chytridiomycosis.

This is a deadly disease that causes the frog to be lethargic and exhibit bodily abnormalities that result in a quick onset of death.

The body will redden and ulcers will appear paired with body convulsions. 

This disease has become a real pain for Australian frog populations.

A paper published by Environment Australia in 1999 mentioned 11 out of the 60 frog species in Queensland were experiencing decline.

The fungus was first found in Australia in 1989 and has been found to affect only adults, is waterborne, and prefers cooler temperatures. 

Urbanization and Deforestation is Killing Frogs

It is no secret that humans are a very big part of population declines across the world.

Removing a landscape that was previously home to amphibian species to use for human use is detrimental to local populations. 

Urbanization refers to building up an area that was once not occupied by many people. 

When we urbanize an area, it involves removing a large portion of the environment to use for human reasons, like building houses.

What is one thing that will always come with new buildings? That’s right; roads. 

I learned about roads in my population dynamics class in college and it was one of the most interesting subjects I have come across.

Roads will split a habitat in pieces.

Migrating across the road is difficult and could spell out death by becoming roadkill. 

The gene pools on either side of the road become smaller since less new frogs are coming into the split populations.

Mortality increases due to attempting to migrate across a road. This also affects migrating across roads to get to breeding grounds. 

Deforestation means removing a large amount of trees from a single area. 

When I think of deforestation I think of logging and clear-cutting entire areas of forest.

Sometimes, deforestation can also alter the frogs natural wetland habitat by clearing them by drying them up.

Removing vast areas of trees changes the landscape, soil, and nearby waterways. 

A farming family I know in the Catskills of New York State clearcut a region on top of a hill to turn into a field for their cows.

It disrupted the soil and erosion so much that every time it rained it washed out portions of the soil into the stream at the bottom of the hill.

Not only has the landscape at the top of the hill changed drastically, but the stream now becomes dirty too. 

The Pet Trade is a Risk to Frogs

The pet trade refers to the, largely illegal, trading of animals to be kept as pets or part of a collection outside of a zoologic facility.

Reptiles and amphibians became popular pets back when there were no breeders for those animals.

Their only source of collection was taking them directly out of their natural habitat. 

I have a personal story to share about how the pet trade affects wild populations.

I have a Hog Island Boa Constrictor that comes from an island off the coast of Honduras.

Their wild population was eradicated by people taking individuals out of their environments and selling them to be pets.

It is in the process of being restored, but other factors stand in the way now. 

Some pet frogs have been released by people who are not sure what their proper care is, or cannot house them anymore.

This leads to invasive introduced species wreaking havoc on local populations. Think of the Burmese pythons in Florida and Cane Toads in Australia. 

But you can help with frog conservation! 

Check out this article on our page about what you can do to help frogs from your very own home! https://toadsnfrogs.com/frog-conservation/

Sources

Declines and disappearances of Australian frogs. (n.d.). Retrieved from https://www.researchgate.net/profile/David-Newell-6/publication/49250879_Status_of_rainforest_stream_frogs_in_north-eastern_New_South_Wales_Decline_or_recovery/links/02e7e5270b8c0cb4a5000000/Status-of-rainforest-stream-frogs-in-north-eastern-New-South-Wales-Decline-or-recovery.pdf?origin=publication_detail 

Ferraro, T. J., & Burgin, S. (n.d.). Review of environmental factors influencing the decline of Australian Frogs. Herpetology in Australia. Retrieved from https://www.researchgate.net/profile/Shelley-Burgin/publication/249963131_Review_of_environmental_factors_influencing_the_decline_of_Australian_frogs/links/5adade090f7e9b28593e6cb3/Review-of-environmental-factors-influencing-the-decline-of-Australian-frogs.pdf 

Hale, S. F., Jarchow , J. L., & Bradley , G. A. (1999). Effects of the Chytrid Fungus on the Tarahumara Frog (Rana tarahumarae) in Arizone and Sonora, Mexico. In P. C. Rosen (Ed.), Connecting Mountain Islands and Desert Seas (pp. 407–412). essay, USDA Forest Service . 

Weldon, C., du Preez, L. H., Hyatt, A. D., Muller, R., & Spears, R. (2004, December). Origin of the amphibian chytrid fungus. Emerg