Brown Booby

Sula leucogaster

Boobies and Gannets are collectively called Sulids (family Sulidae), and can be found globally in many tropical and temperate oceans. The Brown Booby has a world-wide range.

Science recognises four subspecies of Brown Booby:

• S. l. plotus lives in the Red Sea and western tropical Indian Ocean, and east to northern Australia and the central Pacific Ocean.
• S. l. brewsteri lives in the extreme eastern tropical Pacific, including the Gulf of California. And also Tres Marías Island, Clipperton Island, and others.
• S. l. etesiaca lives in the humid regions of the Pacific coast of Central America and northwestern South America south to Colombia.
• S. l. leucogaster lives in the southern Gulf of Mexico, the Caribbean and in the tropical Atlantic Ocean.

Evolution has provided Sulids with special adaptations to accommodate their foraging style. One of which are the closed external nostrils. But also the secondary nostrils beside the mouth that are covered by moveable flaps when the bird plunge-dives into the sea. They also have a spongy bone plate at the base of their bill to act as a shock absorber. This cushions the impact when they hit the water. They also have special membranes to guard their eyes from the impact force of their dive.

These birds can put on a spectacular foraging display when they find dense concentrations of small to medium-sized fish. These are sometimes called bait balls. They often gather by the hundreds or even thousands, over a bait ball, diving at speeds of 50 to 60 miles per hour, and plunging arrow-like to catch their prey. Most dives are relatively shallow, but they may dive more than 70 feet below the surface to secure a meal.

These birds often range up the Pacific coast in Southern California. I found the birds pictured here in Mexican waters during seagoing science expedition in February 2017 to the islands of the Revillagigedos.