The sex of wild turkeys should be determined by looking at the breast feathers.

MALE- Breadt feathers are black tipped

FEMALE-Breast feathers are brown or buff tipped

The males usually have a beard on their chests. At some point it becomes obvious because of the plumage but the beard may be the easiest way to tell.

http://www.agfc.com/hunting/Pages/Huntin...

http://dnr.wi.gov/files/pdf/pubs/wm/WM02...

By examining their undercarriage and if they have a dick then it makes them male.