Ten species of frogs can be observed in outdoors Minnesota. One of these is known as the common, or gray, tree frog.
Since mid-May and now into June, the males have been vocal with their strong trills. These 2-inch-long frogs with their conspicuous finger and toe disks are the ones we see on screens and windows. They're there to feed on insects attracted by the lights in a room on summer evenings.
These small insect- eaters produce a sticky substance on their toe pads that allows them to climb smooth surfaces (such as window panes) without difficulty.
I have noticed that common tree frogs vary greatly in color at different times, usually when the temperature, humidity or habitat changes. Their dorsal (top) sides can change colors from tones of green to gray to brown within a few minutes. The frogs have an unusual control of chromatophores, or pigment-containing cells, in the skin.
Common tree frogs are found in a variety of woodland habitats except in the southwest part of the state. On June evenings, the males continue their melodic calls from woodland ponds. They are well out in a foot or two of water, supported on sunken tree branches or water plants. These enchanting, loud trills each last about two seconds and consist of 10 to 20 separate notes. The vocal sac under the chin is partly inflated between calls, and expands fully and vibrates when calls are produced.
Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. He taught and worked as a naturalist for 50 years.