“A number of state wildlife agencies as well as FWS claim the right to not only enter private property, but in some cases to plant cameras as well, without either a warrant or the property owner’s permission. For example, a chapter of the FWS policy manual denoting “circumstances where a Service officer may observe and obtain evidence without courts considering it a search” stipulates, “when Service officers enter onto open fields…their observations are reasonable under the Fourth Amendment.”
The open fields doctrine dates back to the Prohibition-era Supreme Court decision Hester v. United States (1924). Revenue agents caught a bootlegger with jugs of moonshine. He was on his property but away from his home. He sued to overturn his arrest, as the officers were on the property without a warrant. Writing for the majority, Justice Oliver Wendell Holmes upheld the arrest, finding that “the special protection accorded by the Fourth Amendment to the people in their ‘persons, houses, papers, and effects’ is not extended to the open fields.”
Decades later, the Court affirmed the decision in Oliver v. United States (1984): Justice Lewis F. Powell Jr. held that “in the case of open fields, the general rights of property protected by the common law of trespass have little or no relevance to the applicability of the Fourth Amendment.” Further, “steps taken to protect privacy,” like fences or “No Trespassing” signs, “do not establish that expectations of privacy in an open field are legitimate in the sense required by the Fourth Amendment.””