Wikipedia does have a pretty liberal copyright policy, but with reference to the source, if I remember correctly.
I just looked up Wikipedia's
policy on external use, which follows:
"Wikipedia's textual content is copyrighted, but you may reuse it under the terms of our licensing requirements, summarized below.
Text in Wikipedia, excluding quotations, has been released under the GNU Free Documentation License (or is in the public domain), and can therefore be reused only if you release any derived work under the GFDL. This requires that, among other things, you attribute the authors and allow others to freely copy your work. (This is a summary, see the licence text for the exact details.)
If you are unwilling or unable to use the GFDL for your work, use of Wikipedia content is unauthorized. Small quotations of Wikipedia content, with its source attributed, may be permissible under the "fair use" clause of U.S. copyright law. See Wikipedia: Citing Wikipedia for information about the proper citation of articles. No permission is needed to create a hyperlink to Wikipedia or its articles."
All three examples that I found this afternoon were entirely unattributed.
I have no particular objection to something like "Wikipedia aptly describes this species as 'a drab, unobtrusive foliage-gleaner fond of dense thickets'". These entries, however, were engaging in wholesale copying. Aside from issues relating to copyright and plagiarism, there are several good practical reasons to avoid this:
1. Propagation of error. These things will commit us to tracking the external wikipedia page, lest we continue to spread errors introduced over there. (And they're bigger than we are, so they will attract more vandals and kooks.)
2. Problems of style. The narrative style of the wikipedia articles on the nightjar and leaf warbler had been dismembered to fit the various pieces into our opus format. A variety of wikipedia styles were present (such as the citation tag), while a bunch of things we take for granted (that other species link to the opus entry, for example) were missing. Fixing these things, especially where taxonomic differences will inevitably appear, is almost as much trouble as writing a new entry from scratch.
In short: borrowing paragraph-length material from wikipedia is a bad idea, and I will continue to delete on sight unless convinced otherwise.