States have been allowed to divide their hunting period for most species and groups of birds into 2 or sometimes 3 nonconsecutive segments in order to take advantage of species-specific peaks of abundance. Generally, special seasons focus on those species considered to be more lightly utilized than others. Special seasons are usually, but not always, in addition to the regular season. Special seasons currently exist for some teal, wood duck, sea duck, and resident Canada goose populations. There are a number of other regulatory tools.
Closed seasons occur when a species' abundance is insufficient to withstand harvest.
For example, canvasback seasons, which currently are open, have been closed in the recent past. Permits are effective regulatory mechanisms that allow hunters to take a limited number of birds of a certain species. Recent examples of the use of permits have been with some Canada goose populations and with tundra swans. Quotas are defined as predetermined apportionments of a limited resource. Recent examples of quotas have been with some Canada goose and sandhill crane populations.