Jeremy Irons narrates this National Geographic documentary that examines the declining population of lions in Africa, by focusing on one lioness in a remote part of Botswana. After losing her mate, she and her three cubs stake out territory on an island also inhabited by aggressive buffalo. The scenery is lovely, and the lead lioness is a beautiful animal; footage of her hunting buffalo in the water is thrilling. (The sensitive should be forewarned: There's some on-camera killing, including that of baby animals.) But Last Lions, directed by Dereck Joubert, also employs popular cheats of the genre, such as creative editing, the use of slow-motion photography and appending a soapy narrative. Can't beasts just be the magnificent creatures they are, without some filmmaker adding a family melodrama and descriptors like "single mother"? A well-made documentary that sticks to the facts can be just as fascinating, if not more educational. Carmike 10, South Hills, ongoing. Starts Fri., April 22, at Oaks.