It is true. And here's why, as stated by Jim Spencer in a recent article:
Back in the gloomy, turkey-starved days of the 1930s, 1940s and 1950s, everybody thought turkeys were on a slick downhill road to extinction. Finding a gobbler track in the mud was an event, and if you went hunting and actually heard a turkey gobble, that constituted a successful hunt. Nobody realistically thought they’d actually kill one, and if the stars somehow aligned perfectly and the unthinkable happened, it was picture-taking time in the street in front of the newspaper office.
Given that degree of scarcity, if a hunter by some stroke of good fortune managed to locate a gobbling turkey, you can bet your last ThermaCell cartridge he was going to work that bird conservatively — as in yelp softly three times and then don’t call again for at least an hour. They figured, and rightly so, that turkey hens were as scarce as turkey gobblers, and the gobbler didn’t have many more prospects than did the hunter.
Also, they figured the less they called, the lower their odds of hitting a sour note. Because the common theory of that day held that a hunter’s calling had to be flawless if he was to have any remote chance of success, the standard procedure for the old-timers was to call very infrequently.