The US oil slick could become an environmental disaster if it engulfs major breeding and nesting grounds - such as the Breton National Wildlife Refuge off Louisiana.
Herons are among the species living in the Louisiana wetlands. The National Audubon Society, a US conservation group, has warned of a possible "catastrophe for birds".
The coastal marshes are also home to the clapper rail (pictured) and the mottled duck. Recovery efforts would be difficult or impossible if oil accumulates in their habitat, conservationists say.
Reddish egrets have seen their numbers dwindle because of habitat loss in the region. They have nowhere to go if their feeding and nesting grounds are covered in oil.
Migratory birds such as the Caspian tern, which are nesting in the area, could also suffer from the oil slick.
Several species of sea turtles are at the peak of their nesting season and may become coated in oil as they pass through the Gulf to nest on Alabama beaches.
Conservationists say endangered sperm whales, who hunt for prey at deep water in the northern Gulf of Mexico, may also be at risk if they come up in the slick. Other vulnerable sea mammals include dolphins.
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