Coyote_220--We collected about 300 females for analysis of reproductive performance (1980-87) about 1/2 of which came from Montana as far west as the Jordan country.
Peak of whelping was around 15 Apr, annually. However, whelping by individual females occurs for about 50 days around this peak date (20 Mar-10 May). This occurs, because not all females come into estrous (peak is about 15 Feb, annually) at the same time. Gestation is about 63 days in coyotes.
Pups are about 4 weeks old before they come above ground for the 1st time, and will be about 1/2 grown by mid-late July.
I would suspect that these data would be at least reasonably similar to what you might expect to see in the Butte country.
What do you guys in other areas see in your respective areas re: whelping dates?