Migratory birds may seek respite within trees or on buildings considered private property. The Migratory Bird Treaty Act of 1918 prohibits the removal of all listed species or their parts (feathers, eggs, nests, etc.) from such property. However, in extreme circumstances, a federal permit might be obtained for the relocation of listed species (in some states a state permit is required "in addition" to a federal permit). Pursuant to the spirit of the treaty, it is not trivial to obtain a permit; the applicant must meet a certain criteria as outlined in Title 50, Code of Federal Regulations, 21.27, Special Purpose Permits.