Bird identification?

Hi, so I went walking today and saw a whole flock of brown-gray birds. They weren't something i've seen before, and they don't show up as a common bird species in my area. They were around the same size as an American Robin, but had the slender bill and body of a flycatcher. The call was a grating trill. I guess there isn't any gender dimorphism, because they all were the same colour. I live in Southern Ontario