Brainerd, MINN. – When Minnesota's 2013 duck hunting season opens at one half-hour before sunrise on Saturday, hunters who have found a hot spot will see a variety of duck species. In some locations of the state, up to a dozen or so species might buzz hunters' decoys on the opener.

But four species dominate Minnesota's opening day kill. They are — in order of abundance in hunters' bags — blue-winged teal, wood ducks, mallards and ring-necked ducks.

Hunters should not expect to bag, or even see, brilliantly colored drakes such as those we observe later in the season, once the birds have completed molting their muted brown feathers. Blue-winged teal drakes, for example, won't be displaying the slate-blue heads and crescent moons in front of the eyes. These adornments are reserved for springtime drakes. Instead, hens and drakes will appear so similar, the average hunter will be unable to distinguish the sex on plumage alone.

Most drake mallards are still in what is called "eclipse plumage," meaning the birds have not attained the emerald green heads, brown chests and white bellies we associate with drake mallards shot a few weeks after the opener. The nickname "greenhead" rarely applies to opening day drake mallards.

Sometimes early season drake mallards can be differentiated from a hen only by the color and length of the bill. A drake's bill is olive green and slightly longer is proportion to its head, whereas a hen sports a bill that is dull orange and brown and a bit shorter in proportion to its head. This is important information since the daily limit on mallards is four, but only two can be hens. A novice duck hunter who has shot what he or she thinks are two hens might, upon closer examination of the bill, discover both kills are drakes.

Ring-necked ducks bagged in early season are also more drab-colored because they generally have not finished molting, either. Also, the rings on the bills of both sexes will he lighter and less distinct than later in the season.

Ring-necked ducks, often called ringbills for obvious reasons, are the fourth most common duck in Minnesota hunters’ opening day bags.

The one exception to the rule of drab early season plumage is the wood duck. Mature drakes generally complete their molt earlier than the species previously mentioned, so their plumage is complete, or nearly so, by opening day. Young drake wood ducks usually complete their molt to adult feathers later in the fall. Yet they sport enough adult plumage to be easily differentiated from hens.

Bill Marchel, an outdoors writer and photographer, lives near Brainerd.