Wood ash can be rich in calcium and birds may resort to various
unsual sources for this key nutrient so its a good possibility thats
what they were after, from
http://physrev.physiology.org/cgi/content/abstract/81/4/1567
"Most birds eat insects and/or plants that are relatively low in calcium,
so these cannot fulfill calcium requirements. For some species, restricted
calcium availability limits geographical distribution. However,
many others supplement their diet by eating calcium-rich material such
as bones, owl pellets, mortar, grit, and the shells of snails, crabs,
marine mollusks, and other birds. Boreal chickadees consume ash rich in
calcium; sandpipers eat grit, lemming bones, and teeth; sandwich terns
eat shell fragments; and crossbills in coniferous forests eat bones,
putty, and cement. Graveland provides a table of literature citations
covering 28 species of birds that consume calcium-rich material."
And specific observations at:
http://elibrary.unm.edu/sora/Wilson/v101n02/p0349-p0351.pdf
http://elibrary.unm.edu/sora/Auk/v111n03/p0755-p0756.pdf
Andrew
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