The Secretary of the Interior is authorized to cooperate with the Secretary of Agriculture of Puerto Rico, the Governor of Guam, the Governor of American Samoa, the Governor of the Commonwealth of the Northern Mariana Islands, and the Governor of the Virgin Islands, in the conduct of wildlife-restoration projects, as defined in section 669a of this title, and hunter safety programs as provided by section 669g(b) of this title, upon such terms and conditions as he shall deem fair, just, and equitable, and is authorized to apportion to Puerto Rico, Guam, American Samoa, the Commonwealth of the Northern Mariana Islands, and the Virgin Islands, out of the money available for apportionment under this chapter, such sums as he shall determine, not exceeding for Puerto Rico one-half of 1 per centum, for Guam one-sixth of 1 per centum, for American Samoa one-sixth of one per centum, for the Commonwealth of the Northern Mariana Islands one-sixth of 1 per centum, and for the Virgin Islands one-sixth of 1 per centum of the total amount apportioned, in any one year, but the Secretary shall in no event require any of said cooperating agencies to pay an amount which will exceed 25 per centum of the cost of any project. Any unexpended or unobligated balance of any apportionment made pursuant to this section shall be available for expenditure in Puerto Rico, Guam, American Samoa, the Commonwealth of the Northern Mariana Islands, or the Virgin Islands, as the case may be, in the succeeding year, on any approved project, and if unexpended or unobligated at the end of such year is authorized to be made available for expenditure by the Secretary of the Interior in carrying out the provisions of the Migratory Bird Conservation Act [16 U.S.C. 715 et seq.].