I think one of the biggest issues is overmowing in the fields around Vancouver. I've noticed a lot of unnecessary mowing and haying in perfect fields for killdeer nesting. I'm sure that development and human footprint activity aren't helping.
Last year I could easily identify at least 20 killdeer around my place on any given day. Now I'm lucky to see 2 in one week. That same killdeer at WSUV seems to keep showing up, too. I haven't seen any big gatherings of them there, just that one.
Please keep an eye out for killdeer populations. If you see them somewhere, make a note of it (preferably here!). I consider killdeer to be an important indicator species of field habitat around here...which is disappearing.