That rumbling from grassy meadow? Likely leopard frogs

Something is coming up from the bottom of Minnesota lakes and ponds, and it is green and brown and spotted.

Enter the leopard frog, common in Minnesota. Its maximum body size is about 4 inches. These frogs usually get active in late March after spending the winter in watery depths. Almost immediately they become conspicuous by starting out for temporary meadow ponds for breeding, often crossing highways as they go. Warm, foggy or rainy nights impel them to move in great numbers; many are killed by the traffic. In the fall, large numbers cross the roads again on warm, wet evenings as they move toward their winter homes.

Now is when we hear a new sound coming from flooded grassy meadows. The sound is the low, guttural croaking of male leopard frogs, calling to females. The deep snoring of the male leopard frogs in breeding ponds, a sound somewhat like that of a person rubbing his thumb over a wet balloon, can be heard from late March until early May. Several thousand eggs constitute a single mass, which is usually placed around dead twigs or grass stalks, from a few inches to a foot beneath the surface in shallow water. Then, males fertilize the eggs.

Weather conditions have a marked effect on the period of development of the eggs and tadpoles, but about three months are required for the passage of the two stages until the one-inch long new frogs leave the ponds.