I was out for a bit yesterday and found this guy singing. I found quite a few other Horned Larks perched and singing too. Horned Larks are one of our earliest breeding birds in Montana and I would guess that it is the earliest nesting passerine here. Tony Leukering noted the Colorado Breeding Bird Atlas noted fledgling Horned Larks in Colorado as early as April 7th, meaning that the nest was initiated in early March and he suggests that there may be a few pairs that nest even before that.
The earliest I have observed fledged Horned Larks in Montana was May 6th, although this was in Valley County and there are most certainly birds further south in the state around Billings that nest earlier than that. Although probably not quite as early as in Colorado, I would bet that the birds around here might not be too far behind that. The photo below shows the female and that recently fledged chick I observed in May.