252 U.S. 416, 40 S.Ct. 382, 64 L.Ed. 641 ( 1920)
By a treaty of 1916 the United States and Great Britain undertook the regulation and Protection of birds migrating between Canada and various parts of the United States. An act of 1918 gave effect to the treaty by establishing closed seasons and other rules. The State of Missouri brought a bill in equity to prevent a game warden of the United States from enforcing the act, and appealed from the District Court's dismissal of the bill.
MR. JUSTICE HOLMES delivered the opinion of the court. . . .
. . . the question raised is the general one whether the treaty and statute are void as an interference with the rights reserved to the States.
To answer this question it is not enough to refer to the Tenth Amendment, reserving the powers not delegated to the United States, because by Article II, §2, the power to make treaties is delegated expressly, and by Article VI treaties made under the authority of the United States, along with the Constitution and laws of the United States made in pursuance thereof, are declared the supreme law of the land. If the treaty is valid there can be no dispute about the validity of the statute under Article I, §8, as a necessary and proper means to execute the powers of the Government. The language of the Constitution as to the supremacy of treaties being general, the question before us is narrowed to an inquiry into the ground upon which the present supposed exception is placed.
It is said that a treaty cannot be valid if it infringes the Constitution, that there are limits, therefore, to the treatymaking power, and that one such limit is that what an act of Congress could not do unaided, in derogation of the powers reserved to the States, a treaty cannot do. An earlier act of Congress that attempted by itself and not in pursuance of a treaty to regulate the killing of migratory birds within the States had been held bad in the District Court. United States v. Shauver, 214 Fed. Rep. 154. United States v. McCullagh, 221 Fed. Rep. 288. Those decisions were supported by arguments that migratory birds were owned by the States in their sovereign capacity for the benefit of their people, and that under cases like Geer v. Connecticut, 161 U. S. 519, this control was one that Congress had no power to displace. The same argument is supposed to apply now with equal force.
Whether the two cases cited were decided rightly or not they cannot be accepted as a test of the treaty power. Acts of Congress are the supreme law of the land only when made in pursuance of the Constitution, while treaties are declared to be so when made under the authority of the United States. It is open to question whether the authority of the United States means more than the formal acts prescribed to make the convention. We do not mean to imply that there are no qualifications to the treatymaking power; but they must be ascertained in a different way. It is obvious that there may be matters of the sharpest exigency for the national well being that an act of Congress could not