I'm planning to apply for a postdoc that asks only for a CV and a research statement describing "educational and research background, areas of interest, and what you would like to accomplish in your postdoctoral training."
Does this mean they don't want a cover letter? Should I be essentially merging the cover letter and research statement in one document? Because in a way it just sounds like they're describing what I would expect to be in a cover letter. Or is the cover letter just expected and I should do that plus a research statement?
Unless this is an online application with nowhere to upload it, you should always write a cover letter. It's not hard, and it brings that little extra. It allows you to tell your story the way you want it.
Even if there is nowhere to upload /send a cover letter, you should add a small "summary" at the top of your CV (one paragraph).