During my Bachelors of Science in Fisheries and Wildlife, and certificate in Master Herpetology, I learned about frog and toad migration. It’s a fascinating topic I am excited to share with you today.
Frogs migrate from terrestrial non-breeding habitats to aquatic breeding grounds seasonally. Migration is the movement from one place to another and for frogs it is related to their body size. Migration poses risks to the individuals but is beneficial for organisms with complex life cycles.
In this article we will discuss why frogs migrate and to where. What challenges do they face along the migration route? What times of year do they migrate?
We will talk about their life cycles and its importance in migrational patterns and timing. We will also discuss how humans play a role in the survival of migratory amphibians.
Why Do Frogs Migrate?
Frogs migrate solely for breeding and spawning of their offspring. They do not need to migrate for the winter as they are well adapted for dropping temperatures. Migration brings frogs to breeding grounds where they may find a mate and lay their offspring as eggs in an aquatic setting rather than a terrestrial habitat.
Frogs, toads, and other amphibian species migrate seasonally to large aquatic breeding grounds.
Many species live in terrestrial habitat during the year, which is unsuited for rearing offspring.
Migrating to the breeding ground makes it easier for the frogs to find a mate and deposit their eggs safely.
Breeding grounds attract large numbers of amphibian species to mingle, breed and deposit their eggs.
In terrestrial habitats, they might not find many suitable mates or have an appropriate location to spawn their eggs.
Coming together in a large aquatic setting allows more mingling and provides a safer expanse for the eggs.
Frogs do not migrate to find warmer climates.
Toads burrow underground below the frost line during winter in cold climates, and aquatic frogs find refuge below the surface of ice in oxygen rich water.
Freeze-tolerance refers to the frog’s ability to literally freeze in below zero temperatures and enter a hibernation-like state called brumation.
Frogs migrate for the sole purpose of finding a mate and producing offspring.
Their small body size would make a trek to a warmer climate too taxing and almost impossible. The likelihood of mortality would be greater the longer distance they were to travel.
What Are the Threats to Migrating Amphibians?
Migration brings around multiple threats that could prove harmful or even fatal to the frog.
Some threats are human related, while others may be due to predators or the habitat the individual is migrating through.
Some threats may even come from the animal’s own body if they are not prepared or healthy enough for the journey.
There are multiple human-caused threats to migrating animals.
Habitat destruction and deforestation, like timber harvesting, degrade habitats and may drive the animals out of their terrestrial living grounds.
Humans may change rain drainage routes and reduce aquatic breeding grounds or shorten them.
Roadways are a large burden to migrating frogs and amphibians as well.
Cars will potentially run over animals as they try to cross the road. Some states attempt to put up barricades next to roads to reduce mortality.
Migration requires the frog to potentially venture out in the open, making them more susceptible to predation.
Many animals fall prey to predatory animals while crossing unknown territory or open areas with little cover.
Migrating requires a lot of energy to be exerted by the frog. That is why body size plays a role in how far the frog moves during migration.
The larger individuals will be more capable of migrating greater distances.
Do Frogs Migrate To and From the Same Places?
Frogs tend to migrate toward the highest quality aquatic environment.
This helps with reproductive success, the chances of the frog breeding, and the survival of the eggs. Breeding grounds are seasonal or permanent and frogs usually return each year.
Since breeding grounds for frogs need to be large enough to keep predators at bay and allow room for all the frogs coming, they are usually permanent aquatic areas or seasonal. A seasonal aquatic habitat is mostly the result of flooding after heavy rains or snow thawing.
After breeding is done and the eggs are laid, frogs will return to their non-breeding terrestrial habitats until next season.
They will travel the same route each year back and forth from their terrestrial territories to their breeding grounds. Frogs tend to return to the same breeding grounds over and over.
Spring migrants will rely on their fat storages from the previous fall to provide them the energy to get them through overwintering and migration.
Since migration occurs every year, frogs are well adapted to overwinter in their non-breeding habitats.
This article was written by Melissa M. who holds a Bachelors of Science in Fisheries and Wildlife Sciences, and a Master Herpetologist certificate. The article was edited and published by Daniella, Master Herpetologist in the author profile below.
Kalman, B., & Smithyman, K. (2002). The Life Cycle of a Frog . Crabtree Publishing Company.
Ponsero, A., & Joly, P. (2009, July 20). Clutch size, egg survival and migration distance in the agile frog (Rana Dalmatina) in a floodplain. Archiv fur Hydrobiologie. Retrieved from https://hal.archives-ouvertes.fr/hal-00364739/
Rittenhouse, T. A. G., Semlitsch, R. D., & Thompson, F. R. (2009, June 1). Survival costs associated with wood frog breeding migrations: effects of timber harvest and drought. Ecological Society of America. Retrieved from Survival costs associated with wood frog breeding migrations: effects of timber harvest and drought