Writing for the majority, Justice William O. Douglas cited the ad coelum doctrine. “In a world without airplanes, this doctrine seems at first glance reasonable. But, air travel makes the doctrine unfeasible. As Douglas correctly noted in his opinion, the ad coelum doctrine “has no place in the modern world. The air is a public highway, […] Were that not true, every transcontinental flight would subject the operator to countless trespass suits.”
Douglas went on to argue that the Causbys and other landowners own “at least as much of the space above the ground as they can occupy or use in connection with the land.” Douglas didn’t elaborate on when this enjoyment of airspace ends, he didn’t have to. Whatever the limit, it was clear that at least a partial taking had occurred when planes flew 83 feet above the ground around Causby’s property, causing deadly disturbances to the farm’s avian residents.
Given that every day tens of thousands of flights take place in American airspace some sections of the air should be treated like public roads. In other contexts, such as the Fourth Amendment, the Supreme Court has twice considered whether police officers need a warrant to observe private property from aircraft and both times ruled that police officers do not need a warrant to search a private residence from the air.
In 1986, in California v. Ciraolo, the Court ruled that officers did not need a warrant to search a backyard for marijuana plants from an airplane at 1,000 feet. Chief Justice Warren Burger wrote that Dante Carlo Ciraolo could not reasonably expect privacy in his backyard, and therefore a warrant wasn’t required.
Then, in Florida v. Riley (1989) the Court ruled that police could use a helicopter hovering at 400 feet to look for marijuana plants in a backyard without a warrant. Like in Ciraolo, the Court ruled that Riley did not have an expectation of privacy, in part because at 400 feet “any member of the public or the police could legally have observed respondent’s greenhouse.”
In a prescient dissent, Justice William Brennan offered a far‐fetched thought experiment for 1989, but which now seems more like soothsaying: