We are very thankful indeed when someone helps the animals by promoting our site. Really many people and sites do. Trying to keep parity with all them, we should host hundreds of banners! The quality of our site would suffer significantly, so we decided to host none.
Why do we not display ADs, it's potential profit for animals
Considering our visitors numbers, it's about very litte money. In return we get something more: recognizability. Web site without any ADs rather sticks in memory. Convenience of our visitors who come for the information, not for ADs, play a role too. And finally considerations of information quality: nobody knows whos ADs will be automatically displayed, and whether we'd like to answer for the advertiser indeed.