Examples:

The Department of the Interior and States are co-trustees for migratory birds.

Federal land management agencies (other than Interior) are co-trustees with Interior, Commerce, and/or States and possibly Indian tribes for most living natural resources on Federal lands.

The Departments of the Interior and Commerce can be co-trustees for certain natural resources: sea turtles are the trust responsibility of Commerce in the water and Interior on land. States are co-trustees with Interior and Commerce for sea turtles both at sea and on land.