The fourth season of The Andy Griffith Show opens with one of the series' finest episodes, as well as the favorite episode of co-star Ronny Howard (now better known as film director Ron Howard). "Opie the Birdman" poignantly details the efforts by Opie Taylor (Howard), son of Mayberry sheriff Andy Taylor (Andy Griffith), to take care of several newly hatched robins after accidentally killing the mother bird with his slingshot. The rest of the season maintains the high standards of this opener, with such classic episodes as "Ernest T. Bass Joins the Army," featuring Howard Morris as the titular rock-throwing village idiot; "A Black Day for Mayberry," in which Andy and his nervous deputy Barney Fife (Don Knotts) prepare for the arrival of a top secret gold shipment from Denver; "Up in Barney's Room," the saga of the acrimonious falling out and tearful reconciliation between Barney and his landlady Mrs. Mendelbright (Enid Markey); "Barney's Side Car," or how a man can be corrupted by a WWI vintage motorcycle; "Divorce. Mountain Style," in which the rambunctious Darling family once more descend upon Mayberry, with a pre-Gilligan's Island Bob Denver along for the ride; "The Return of Malcolm Merriwether," another visit from Mayberry's favorite English valet (Bernard Fox); and the unforgettable "Citizen's Arrest," chronicling a war of nerves between Barney and indignant gas station attendant Gomer Pyle (Jim Nabors). Speaking of Gomer, this would be the last year that this remarkable character would appear regularly on The Andy Griffith Show. The series' season finale, "Gomer Pyle, U.S.M.C.," serves as the pilot for the popular military sitcom in which Jim Nabors would headline from 1964 through 1970. Season four of The Andy Griffith Show found the series still flourishing in the ratings, ranking as America's fifth most popular program.