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Late season frogs

Late season frogs
Ranger Steve Mueller

By Ranger Steve Mueller

Northern leopard frogs were common when I was young and exploring neighborhood wetlands. They have become uncommon and even rare in many locations for reasons unknown. It is not just because I have grown and developed other pursuits that they seem less abundant. Herpetologists studying the frogs confirm decreased numbers. If you have them in abundance, celebrate and protect healthy habitat. We do not understand all the critical features in their nature niche needed for survival.

The pickerel frog is a small North American frog, characterized by the appearance of seemingly “hand-drawn” squares on its dorsal surface. Photo by Brian Gratwicke, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

They begin breeding later in spring than the Wood Frogs, Western Chorus Frogs, and Spring Peepers described in last week’s article. The late season frogs do best in permanent water. Shallow water near lake shores with lots of grassy vegetation, marshes, and moderately slow stream borders and inlets provide good breeding habitat. I think that clearing lake shores of vegetation for better beaches and eliminating vegetation for better swimming areas contributed to frog decline. I have not seen that confirmed by amphibian studies so that hypothesis remains unanswered. 

Removing vegetation chemically or with manual equipment does not bode well for aquatic organisms. People want fish to thrive, but fish are challenged with more sterile habitat as are amphibians, insects, and wetland feeding birds and mammals. 

Pickerel frogs look similar to leopard frogs but can be distinguished by two features. Pickerel frogs have large rectangular dark spots with narrower light areas between them. The leopard frogs’ dark spots are smaller and rounded with greater light color separating spots. More significant is the Pickerel frog’s hidden bright yellow at the base of the hind legs. Leopard frogs might have a faint yellow there. Both frogs normally develop into an adult in one season but some require two summers. That is a reason they do best in permanent waters. Those breeding in late April or early May are more likely to reach adulthood in one warm season. 

Two similar frogs are green and bull frogs. Bull frogs get much larger but that takes time and may require a few years growth. Both usually take more than one year to transform from the tadpole stage to a tailless adult frog. Green frogs line up around the edge of the vernal pond to the west of the Red Pine interpretive building at the Howard Christensen Nature Center. That pond sometimes retains water throughout the winter but not always. Many developing frogs that breed there must die. The permanent tadpole pond southwest of the building offers better survival chances. 

One habitat management policy I implemented when I was director at HCNC was for interpretive teachers to only take students around the west shore of vernal pond to allow the east shoreline to remain undisturbed by school groups. The purpose was twofold. Number one was to teach a respect and reverence for life and secondarily to hopefully improve survival opportunity for frogs in that half of the pond.

Green frogs have what is called a dorsolateral ridge or fold that runs from head toward the rear. This ridge is absent on bull frogs so even smaller bull frogs can be distinguished by the lack of the long ridge. Bull frogs have a ridge that runs from behind the eye and wraps around the flat circular eardrum called a tympanum that is behind and below the eye. Green and bull frogs sing when the temperature warms to above 70ºF making them the latest to join the seasonal orchestra. A green frog sounds like someone plucking a banjo or guitar string. Bull frogs resemble a cow mooing. 

The last late season frog common in our region is the gray tree frog that is medium sized between the wood frog and green frog. It is somewhat toad like in appearance and has suction cup toes and can climb windows. Like other frogs it breeds in water. It moves away from ponds when grown, like chorus frogs, spring peepers, wood frogs, and leopard frogs. These frogs all feed in moist forests but the gray tree frogs seems to tolerate drier areas better. They can be found hiding on the siding of our homes and feed on insects by lights at night. Their call is a sharp short trill unlike the exceedingly long trill of American toads that reside in insecticide free gardens.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.

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