The crossdomain.xml file allows access by some Adobe clients to the APIs at ebird.org. (See http://www.adobe.com/devnet/articles/crossdomain_policy_file_spec.html for more information.) We currently use a single policy file for all of ebird.org. This file is located at http://ebird.org/crossdomain.xml.
We are more than happy to add your domain to this file. Please contact ornith-is-admin@cornell.edu to request this.