War-Maid of Mars" is a very misleading title. Incredibly, this ERBian-sounding story is a direct sequel to "Duel on Syrtis," (see here) which I had thought was a one-shot with a nasty ending. Kreega, the "owlie" (Martian) who defeated a human hunter and looked forward to Martian liberation in "Duel...," is alive and well, still based in Syrtis, and leading the struggle for liberation in "War-Maid..." although, of course, he is not the title character!
Thus, among Poul Anderson's many short series, these two Martian stories could be published as a single volume. What would make a good title?
I do not buy feathered, owl-like Martians, although Anderson would probably have been able to rationalize such organisms inhabiting the Martian environment as it was understood at the time he wrote the story. They sound like the Martians of the first Nicholas van Rijn story, "Margin of Profit," which, when that story was rewritten to fit into the Technic History, were reconceptualized as extra-solar colonists of Mars.
I say yet again: Anderson either systematically examines every possible answer to a question and implication of a concept or at least generates a very good impression of doing so!