By Roger Clay, Wildlife Biologist
The alteration or disappearance of habitat is the main problem faced by wildlife species across the country. What if you are a species that covets some of the same limited habitat coveted by people? You could be in trouble and may need to change some of your ways.
A species that exemplifies this dilemma is the least tern. The least tern is the smallest North American tern and nests in Alabama before venturing south to spend the winter months. Terns are related to the gulls, but are sleeker with more pointed wings. They dive into the water to capture small fish.  In Alabama, least terns are confined to the coastal waters in Mobile and Baldwin counties.
While there may be ample water for least terns to forage, the development and building boom of the Gulf Coast is creating a “housing” shortage. The terns normally nest on open, clean sandy beaches—just as the area’s beachgoers and others favor. As the coast continues to develop, least terns have fewer and fewer places to nest. Even if least terns do find an open beach to nest, there is typically human activity in and around the area that can be disruptive to the nesting birds.
Fortunately the least tern has a couple of factors in its favor. First, the species is a colonial nester. This means least terns nest very close to each other, within a foot or two, so there can be a large number nesting in a relatively small area. Second, least terns will use areas that mimic its natural nesting sites. The use of artificial nest structures is a trait of many bird species. A popular hobby of many property owners is to erect bluebird or purple martin houses. Wrens, wood ducks, woodpeckers, chickadees, and other birds all will use artificial nest structures as long as the birdhouse is the right size and placed in the proper habitat. Even the osprey will use artificial nest platforms, but building an artificial beach for least terns doesn’t seem practical.
One of the unintended consequences of beachfront development has been the construction of artificial nest sites for least terns. The flat, pea-gravel rooftops of commercial buildings serve as substitute nest sites as they mimic the vegetation-free beaches the terns target. An added benefit to birds nesting on rooftops is that they are elevated and away from any foot traffic or other disturbances they would otherwise face on the ground.
Nesting up on a roof does have its drawbacks. Away from the cooling effects of the water’s edge, heat stress to eggs and chicks is greater, and there is no nearby vegetation for chicks to use as shelter. There is also the possibility of flightless young perishing from falls off the edge of the roof. Flooding of nests may occur when water pools in low spots of the roof after heavy rainfall.
Other bird species including black skimmers and nighthawks are also known to use rooftops. As human encroachment grows, the capacity to adapt to changing environments for a species like the least tern will play an even greater role for future survival. For more information on least terns and other birds that use artificial nest structures contact Roger Clay, Alabama Division of Wildlife and Freshwater Fisheries, P.O. Box 247, Daphne, AL 36526.