That being said, Maryland Zoo is a gem of an institution, one that is in no way inferior to the National Zoo... just different. For one thing, it's more spread out and feels wilder than its DC counterpart - there are no rows of animal houses here, and the exhibits are interspaced with more trees and rocks. Even without the budget of the Smithsonian to back it up, many of its exhibits are spacious and attractive, and some are truly beautiful. The opening display for the zoo's African Journey trail features a herd of handsome sitatunga antelope - along with hornbills and cranes - frolicking at the base of a thundering waterfall. The collection may be smaller than National Zoo, but in many ways it's complimentary. Many popular animals that you won't find in DC - penguins, polar bears, giraffes, chimpanzees, rhinos - can be found in Baltimore, and vice versa.
Probably one of the best features of Maryland Zoo is its Children Zoo - once rated the nation's best, and still easily in the top ten. Focusing on the wildlife of Maryland (I'm a sucker for native animal exhibits - every zoo should have one), kids can hop on giant lily pads, explore a labyrinthine cave (complete with a wooly mammoth skeleton playground), pet the goats in the barnyard, or watch river otters swim overhead. I'm pretty sure that every child in central Maryland has been photographed at least once in the zoo's giant model oriole and heron nests, situated in the Marsh Aviary exhibit. Many zoos have built bigger or grander kid zoos since, but Maryland Zoo's children zoo in many ways wrote the original book on introducing kids to nature in a zoo setting.
Maryland Zoo has had many conservation success stories over the years. For example, it's renowned for its involvement in the Mountain Gorilla Veterinary Project and had an active and early role in Project Golden Frog, devoted to saving the Panamanian Golden Frog. The zoo is perhaps known best of all for its breeding successes with African penguins. After having shuttered many exhibits a decade ago, the zoo is finally announcing its first new major exhibit in years - a renovated home for its penguin colony (see news link at bottom). Hopefully, it will be the first of many expansions and renovations. The Maryland Zoo may not be the biggest zoo in the mid-Atlantic, but it is certainly one of the best.