Barred Owls (Strix varia) recently expanded their range to include western North America and evidently are competing with federally threatened Northern Spotted Owls (S. occidentalis caurina). To help protect Spotted Owls, the US Fish and Wildlife Service (USFWS) is considering conducting a 3- to 10-y study in which as many as 2150 to 4650 Barred Owls would be killed and, possibly, carrying out long-term management of Barred Owls (Livezey 2010). To assist in these globally precedent-setting considerations, I present information concerning how frequently range expansions of North American birds and other factors may precipitate similar management issues in the near future. A total of 111 bird species (19.5%) recently expanded their breeding ranges into at least 1 new state or province. Fourteen species expanded their ranges into more states and provinces (range = 13–46) than did Barred Owls (n = 12). Thirty-eight states or provinces have at least 10 more bird species than they did centuries ago. Human-caused changes to habitat (n = 84) or climate (n = 5) facilitated 98% of known or suggested range expansions, so it is likely range expansions will continue. If thousands of Barred Owls are killed because they expanded their range and are competing with a species of concern, it seems likely USFWS soon would need to consider whether to lethally intervene in conflicts between many other species of native birds due to the high frequency and large extent of range expansions, probability that range expansions will continue, increases in number of listed species, and further documentation of negative effects between species.
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Vol. 91 • No. 3