Books these days are going to the dogs. You might even say that the surprise success of Elizabeth Marshall Thomas’ The Hidden Life of Dogs has given the dog-book category a new leash on life. This month’s pick of the litter: Animal Happiness, a collection of essays by Vicki Hearne, an animal trainer, poet, and philosopher who has been called ”the most important animal thinker since Konrad Lorenz.” Though Hearne’s book includes everything from parrots and orangutans to ornamental carp, she writes most fetchingly about dogs. ”My own happiness (has) a lot to do with Airedales,” explains Hearne, who is also narrative consultant for the National Pit Bull Terrier Defense Association and Literary Society. Pit Bull Literary Society? Not so startling a concept when you consider that there are more dog books out there than you can shake a stick at. Teaching Rover to heel his inner puppy? Most bookstores feature a sizable self-whelp section, including such pup-psychology titles as When Good Dogs Do Bad Things, The Body Language and Emotion of Dogs, and How to Talk to Your Dog. Want a pedigree with serious mental wattage? Stanley Coren’s The Intelligence of Dogs, due out this spring, ranks 79 breeds by intelligence. Then there’s photographer William Wegman’s humorous new series of picture books featuring his famous weimaraners in fairy-tale regalia. If every dog book has its day, The Hidden Life of Dogs is the current leader of the pack. An anthropologist and novelist, Thomas writes as if she’s Margaret Mead casting a sequel to Beethoven’s 2nd. Now, I’m as guilty as anyone of anthropomorphic foolishness, but my short-haired pointer has a hidden life so obscure she seems to have misplaced it. And when Thomas describes a wanderlusting Siberian husky as ”a husband,” ”Odysseus,” and ”a civil engineer,” it’s tempting to dismiss her observations as, well, doggerel.