The Lake Pontchartrain Causeway in Louisiana serves as a unique aerial highway for brown pelicans, known for their distinctive features like a seven-foot wingspan and elongated reddish beaks. These pelicans exhibit a specific flying behavior alongside the bridge, seemingly gliding effortlessly next to vehicles moving at high speeds. The reason for this behavior is their utilization of updrafts created by the bridge, a phenomenon called a "declivity current."
The wind blowing over Lake Pontchartrain hits the causeway, deflecting air upward and generating an updraft at the roadway deck level. Pelicans take advantage of this phenomenon to conserve energy in their flights to and from feeding grounds. They appear to ride the air cushion produced by the bridge, covering the entire 24-mile length without flapping their wings. Pelicans, with their large wings, are expert soarers, employing various environmental factors such as wind speed and air pressure to enhance their flying efficiency.
Other bird species, like purple martins, cormorants, and gulls, also benefit from the Causeway. Purple martins nest under the bridge, while cormorants and gulls perch on utility buildings, using the reflected heat for warmth. The article highlights the conservation success story of brown pelicans in Louisiana, which faced local extinction in the 1960s due to pesticides but were reintroduced through the efforts of scientists who brought pelicans from Florida. The presence of these birds on the Causeway is considered a special sight and a testament to successful conservation efforts over the past few decades.
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https://www.nola.com/news/northshore/pelicans-surf-along-causeway-guardrails/article_eafbf192-84a7-11ee-b416-3bac029fbc52.html