There is a noticeably pungent odor along the Buffalo Bayou at Waugh Drive. The acrid smell of ammonia is especially strong on the jogging path under the bridge. It is there that you will find Houston's foremost colony of bats.

Since at least 2003, and possibly earlier, a colony of Mexican Free Tail bats have taken up residence in the Waugh Drive Bridge. The original, long span bridge was built between 1922 and 1924 to replace an earlier low water crossing. It was named for Private Tom T. Waugh who died in World War I. His father, T. L. Waugh was city's street and bridge commissioner. The current bridge is a modern structure with a box beam design using large concrete slabs with beams separated by expansion joints. The expansion joints are 3/4 to 4 inches wide and 16 inches deep, and those cracks provide an ideal nesting place for the bats. The bridge, which spans the length of the bayou gorge, provides ample room for the 250,000 to 300,000 bats who make up the colony. 

Although this colony is much smaller than the 1.5 million bats of the colony in Austin, the Houston Waugh Drive bats are unique in that they apparently do not migrate. Mexican Free Tail bats (Tadarida brasiliensis) usually arrive in March and return to Mexico in November. The Waugh Drive colony is here all year around.

The best time of year to see the bats is in July and August. The bugs in Houston are at their best in late summer, and the bats have had their "pups" so both mothers and babies are foraging for mosquitoes and insects along the bayou. Shortly before dusk, the activity of the colony begins under the bridge. For the next hour or so, bats can be seen swarming under the bridge. However, unlike the dramatic exits of other colonies, such as those in Austin or at Carlsbad Caverns, the Waugh Drive colony does not exit in a black cloud against the dimly lit sky. Rather, these bats head right down the bayou toward downtown, catching food on the wing that inhabits the trees and brush on the banks of the bayou.

The best place to see the bats is at the Waugh Bat Colony Observation Deck on the south bank of Buffalo Bayou at Waugh Drive and Allen Parkway. The deck, donated by the Lyondell Chemical Company and dedicated in May, 2006, provides a convenient spot from which to await the bat activity each evening.