Wood frogs (Rana sylvatica) are the first to start calling around Duluth. The wood frog call is usually described as 'quark-quark-quark' or duck-like. Wood frogs are easily recognizable by a dark mask and white lip line. In overall color they range from light to dark brown and sometimes are pink or reddish.
To see when frogs begin to call across North America see the map at Journey North Spring 2011 - First Frogs
Next week I'll give some tips on identifying wood frog eggs (along with photos).