It may be a little late for spring burns, even in Wisconsin, but I'm pretty sure it is too early to worry much about ground nesting birds. Some of the sparrows, meadowlarks, bobolinks, etc., may be arriving by now (at least here in MO), but nesting will not really occur in earnest for another month or so, and eggs and nestlings for a while after that. And birds will re-nest if they are disturbed, especially so early in the nesting season.

The decision to burn in late winter/spring or late summer/fall depends on your site and your management goals. The conventional wisdom is that spring burns favor warm-season grasses and fall burns favor forbs, but I'm sure that is an over-simplification.

The thing about spring vs. fall burn favoring grasses or forbs should hold true if burns are carried out the same time of year over a period of years.

not too late in wisconsin to burn.

when the maple trees flower is too late. unless ur trying to do something specific...like kill out a specific cool season grass like canary reed grass. then i would burn even later than that general rule of thumb.

froggy