I think most the zoos in Holland really do do their best to be productive and not just entertainment. Something I stumbled upon a week or two ago was this: Blijdorp, a zoo in Rotterdam, which belongs to one of the best conservation projects in Europe, is now also striding to help the rainforests in Congo and whilst doing that protecting the natural habitat of the gorilla.
They are doing this by collecting old mobile phones and working together with a company which gives a certain amount of money for each collected mobile and recycles the wolfram used in the mobile. The reason Blijdorp is collecting mobiles to be recycled, is because the metal in it is escavated in the rainforests of Africa and by recycling it there is less need to destroy more forest. Also, the total amount they get from the company is spent on helping the gorillas in Congo.
There are different ways of handing in your old mobiles: there are dispensers in the zoo itself, or you can send of for special enveloppes to send your old phones to them and without postage costs.
Personnally I think this really simple way of raising money in a way everyone can join in, is a fantastic project and hope more zoos all around the world will take notice and also find ways like this to help nature a little bit more!
Here is a link for the Dutch among us who are interested:
Diergaarde Blijdorp - Mobieltjes voor gorilla's