Not 100% sure of Cisticola ID, but it's my best guess.
Perching on ground is a behavior for A. sitchensis identified in Hudson and Armstrong field guide of Alaskan odonates.
male & female
Apparently these warblers can be quite common locally, but I had never seen so many -- so active -- in one place.
This yellow warbler looked a little different than the others flitting around. It has a chestnut patch above the eye -- perhaps a sign of gradation with the more southern mangrove subspecies which has a very conspicuous chestnut head?
Not absolutely confident that these are yellow (and not grey) wagtails, but I think there's enough yellow on nape and back.