16 USC 718a - Prohibition on taking

(a) Prohibition 

(1) In general 
Except as provided in paragraph (2), no individual who has attained the age of 16 years shall take any migratory waterfowl unless, at the time of the taking, the individual carries on the person of the individual a valid Migratory Bird Hunting and Conservation Stamp, validated by the signature of the individual written in ink across the face of the stamp prior to the time of the taking by the individual of the waterfowl.
(2) Exception 
No stamp described in paragraph (1) shall be required for the taking of migratory waterfowl
(A) by Federal or State agencies;

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(B) for propagation; or
(C) by the resident owner, tenant, or sharecropper of the property, or officially designated agencies of the Department of the Interior, for the killing, under such restrictions as the Secretary may by regulation prescribe, of such waterfowl when found damaging crops or other property.
(b) Display of stamp 
Any individual to whom a stamp has been sold under this subchapter shall, upon request, display the stamp for inspection to
(1) any officer or employee of the Department of the Interior who is authorized to enforce this subchapter; or
(2) any officer of any State or political subdivision of a State authorized to enforce State game laws.
(c) Other licenses 
Nothing in this section requires any individual to affix the Migratory Bird Hunting and Conservation Stamp to any other license prior to taking 1 or more migratory waterfowl.