Here are a few links that I came up with... they concern birds, but many issues also apply to gliders.
One of these pages mention that fruit juices can also 'raise' the metals from the wire. Since a gliders diet consists of over 50% fruit/veg. couldnt they also pass these particular acids through their system?
Just a thought...

http://www.realmacaw.com/zinc.aspl
http://theaviary.com/s1295-66..aspl
http://www.birdsnways.com/wisdom/ww14eii.asp
http://www.parrotsociety.org.au/articles/art_006.asp
http://www.wingedwisdom.com/ww14eii.asp
http://www.wingedwisdom.com/ww14eiii.asp

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