GEE, Circuit Judge:

 Appellants were convicted of violating two federal regulations promulgated by the Secretary of the Interior pursuant to statutory authority conferred on him by the Migratory Bird Treaty Act, 16 U.S.C. s 703 et seq.  These are designed to conserve migratory game, such as the ducks here concerned, by regulating the means employed in taking them.  The regulations here in point [n. 1] generally forbid the use of live decoys (callers) and the use of grain or the [p. 912] like as artificial bait.  They read, in pertinent part:

1. 50 C.F.R. Subpart C, 20.21(f) and (i).

 No person shall take migratory game birds:
(f) By the use or aid of live birds as decoys; although not limited to, it shall be a violation of this paragraph for any person to take migratory waterfowl on an area where tame or captive live ducks or geese are present . . ..
(i) By the aid of baiting, or on or over any baited area.  As used in this paragraph, "baiting" shall mean the placing, exposing, depositing, distributing, or scattering of shelled, shucked, or unshucked corn, wheat or other grain, salt or other feed so as to constitute for such birds a lure, attraction or enticement to, on, or over any areas where hunters are attempting to take them; and "baited area" means any area where shelled, shucked, or unshucked corn, wheat, or other grain, salt, or other feed whatsoever capable of luring, attracting, or enticing such birds is directly or indirectly placed, exposed, deposited, distributed, or scattered . . ..

 On sufficient evidence, the magistrate found that at the time of the offenses charged, appellants were hunting from a duck blind located less than 300 yards from calling live decoys and cracked corn, with ducks flying directly over the blind to these enticements.  He found as well that appellants either knew (Knerien and Richard) or should have known (Delahoussaye) of the presence of the callers and should all have seen cracked corn located in piles along the levee they traversed to get to the blind.  On these findings, he concluded that the blind was in a baited area and that all appellants should have known it was.

 . . . .  We conclude that . . . a minimum form of scienter the "should have known" form is a necessary element of the offense.

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 We also conclude that a minimum the bait or the callers must have been so situated that their presence could reasonably have been ascertained by a hunter properly wishing to check the area of his activity for illegal devices. There could be no justice for example, in convicting one who was barred by a property line from ascertaining that birds were being pulled over him by bait or callers hidden from his view, and we decline to impute such an intent to the regulations.  One mallard sounds like another, or even like a duck call, and the fact that a hunter hears quacking next door does not tell him that callers are in use there.  The same is true of bait; standing crops attract game quite as well as bait does, and hunting over standing crops is expressly permitted by another portion of the regulations not quoted.  If the hunter cannot tell which is the means next door that is pulling birds over him, he cannot justly be penalized.  Any other interpretation would simply render criminal conviction [p. 913] an unavoidable occasional consequence of duck hunting and deny the sport to those such as, say, judges who might find such a consequence unacceptable.  On the other hand, to require a higher form of scienter actual guilty knowledge would render the regulations very hard to enforce and would remove all incentive for the hunter to clear the area, a precaution which can reasonably be required.  Such a reading is unnecessary to the regulations' constitutionality, and we reject it.  Given the magistrate's findings and conclusions, these observations dispose of appellants' major attacks, that on "area" as vague and that on "should have known" as the standard of scienter.

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 Appellants' convictions are AFFIRMED.