Common yellowthroats in North Dakota on the James River

I found a sunflower patch right above the James River in North Dakota that’s attracting lots of common yellowthroats foraging for insects. Not only am I getting lots of photos, but I’ve also enjoyed the chance to observe how these little birds hunt for insects. They nab bugs from the bottoms of leaves as well as on the stalks of the sunflowers. I wonder if these birds were here all summer, or are they migrating south?