Signs of Spring: Amphibians
March 22, 2023
By Annica Brocker, Park Interpreter
Spring is heralded by singing songbirds and the return of the color green to natural spaces that have been largely brown and dormant all winter long. Flowers begin to bloom once more, and animals are becoming more and more active. One group of animals that go from “0 to 100” in terms of activity levels at the start of spring are amphibians.
Amphibians are a group of cold-blooded, vertebrate animals that are characterized by laying jelly-like eggs and having moist, scaleless skin. The most distinguishing characteristic of amphibians is the source of their name. Amphibian comes from the Ancient Greek term “amphíbios” which means ‘both kinds of life’. Almost all amphibians lay their jelly-like eggs directly in bodies of water. When these eggs hatch, the larvae are built for aquatic life, with gills and flat tails for swimming through the water. Most amphibian larvae go through metamorphosis, swapping gills for lungs and gaining the ability to go onto land. Going from fully aquatic to living on land and in water warrants the name ‘both kinds of life’ indeed!
Amphibians in Michigan spend their winters in a period of dormancy know as brumation. Amphibians enter their brumation period as the days shorten and the environmental temperatures drop. Just like mammals preparing for hibernation, amphibians spend their late summer and early fall building up fat reserves. Again, just like hibernating mammals, brumating amphibians experience slower metabolic rates and lower body temperatures. Where they differ however is that mammals maintain their hibernation throughout the entire winter, whereas amphibians may come out of brumation if there are particularly warm days, since their body temperatures are dependent on their environment. This past New Year’s Eve, frogs were seen hopping and calling in some of the Metroparks while groundhogs were still tucked in their burrows!
As amphibian’s are rousing from brumation, males have one thing on their mind: attracting mates. Male newts and salamanders attract females through smell, but in a quite unusual way. Males deposit their pheromones directly on the females by slapping, rubbing, nudging, or butting parts of their bodies. This fight-like, pheromone behavior makes the female more receptive to mating with the male. Like male birds, male frogs and toads produce a variety of species specific calls to lure females. These calls range from peeps, trills, “a plucked loose banjo string”, quacks, or snores. The cacophony these frogs make is unlike anything you have ever heard. All of these mating behaviors occur in a specific place: vernal pools.
Vernal pools are bodies of water that fill with melting snow and spring rainfall and dry up by the end of summer or at the beginning of fall. Because of their impermanence, vernal pools are not great habitats for aquatic turtles and fish. Without the threat of large predators, vernal pools are the preferred egg-laying grounds for amphibians in Michigan, offering a safer space for their aquatic larvae to thrive before they go through metamorphosis. If you closely look on the vegetation submerged in the vernal pools, you will see the hundreds of egg masses that female amphibians have laid waiting to hatch, promising a new generation ready to live both kinds of life.
There are many opportunities to get up close and personal with amphibians in your Metroparks this spring. Check out programs like Vernal Pools are Cool on March 18th at Oakwoods Metropark Nature Center, Vernal Pool Discovery and Frog Fest at Stony Creek Metroparks on April 2 and April 29th, and Salamander Search at Hudson Mills Metropark on April 22. All of our park programming can be found on our website at metroparks.com!