The Michigan DNR’s page on Northern Spring Peeper (Pseudacris crucifer) says:
The tinkling of bells is a popular description of the spring peeper’s spring mating call. Spring peepers are one of the earliest callers among the dozen frog species found in Michigan. During the first warm evenings of spring in late March or early April through May, their distinctive single note, high pitched “peep” is considered a harbinger of spring. The intensity of calling increases and can become a deafening chorus during humid evenings or just after a warm spring rain when many males congregate.
Only the male frogs call. They establish territories near the edge of permanent or ephemeral wetlands. They may call from elevated perches of submerged grass or shrubs near the water. The faster and louder a male sings, the more likely he is to attract a mate.
The female will lay between 750-1,200 eggs. The strings or clumps are attached to twigs and aquatic vegetation. Depending on the temperatures, eggs may hatch within four days or may take up to two weeks during cooler periods. After another two to three months, young tadpoles are fully transformed into young frogs and leave the pond.
They resemble their parents with the most distinctive mark being a dark brown “X” (may be irregular or incomplete on some) on their lighter brown or tan back. They begin feeding on small food items like spiders, mites, ticks, pill bugs, ants, and caterpillars. By the end of the summer, they have reached the adult size of about 1 – 1 1/2 inches. As the days cool, the peepers dig into the soft mud near ponds for the winter. Still, during warm spells into the fall they can be confused and emerge to give their spring mating call.
The spring peeper is the most abundant of Michigan’s singing frogs and is common statewide. They prefer damp woodlands, swamps, and marshes. However, they still need protection – local populations around small ponds and wetlands can be highly susceptible to surface water runoff. These waters can carry chemicals, pesticides, or silt that can kill adults, eggs, or tadpoles. Good soil erosion practices and the careful application of pesticides and fertilizers are good for spring peepers.
The most distinctive thing about peepers is their call, which can become deafening in springtime. The Pseudacris crucifer (Spring Peeper) section from UM Animal Diversity Web has a short peeper call from Livingston County, and you can see a peeper peeping in this video.
Some more peeper particulars: Wikipedia’s Spring Peeper entry notes that their calls can be heard from as far as 1 – 2.5 miles depending on the number of peepers in a pond, that peepers generally like to breed when it is closer to dusk and throughout the evening and early morning hours, and that peepers can live up to 3 years in the wild. At Portage Lake in Washtenaw County, Michigan in the 1950s, surveys in March, April, and May found that spring peepers were the most abundant animals. The page on peepers from watersheds.org notes that spring peepers produce glucose (sugar) in their livers that acts as an anti-freeze and is pumped to vital organs including the heart and lungs to allow them to freeze and thaw without developing ice crystals. Our Peeper-pedia on Absolute Michigan has a few more links and a cool video of a Michigan peeper in action.