Frigates and Boobies Feeding Niche

Above photos by Frank Jordan. Red-footed Booby (left) and Magnificent Frigate (right). Half Moon Caye. June 2019.

One of our favorite bird-bird interactions in the tropics is the attempted dominance by Magnificent Frigates over various species of boobies. The one we see most frequently is between Magnificent Frigates (Fregata magnificens) and Red-footed Boobies (Sula sula) on Half Moon Caye, Belize.

Frigates nesting. Half Moon Caye. Photos by Frank Jordan. June 2019.

The Frigates (both Magnificent and Great – Fregata minor – that we have observed) do quite well feeding on their own. They are adept at grabbing flying fish on or above the surface, other species when the opportunity arises, and landing lunchables including nestling shore and sea birds and lizards. They take squid and cnidarians (jellyfish and the like) near the water’s surface without wetting their feathers.

Red-footed Boobies resting. Half Moon Caye. Photo by Abby Trahant. June 3, 2019.
A baby Booby. Half Moon Caye. Photo by Frank Jordan. June 2019.

Red-footed Boobies feed by divebombing shoals of fish at sea – they see them, fold their wings back and dive headfirst like an arrow into the school, then either grab them quickly or swim a bit before capturing prey. They then swallow them for transport back to the nesting colony. They may dive from altitudes of 30 m (about 100 ft) or above, and hit the water at speeds of 100 km/hr (60 mph). Since this is done many times each day, it is wearing on the eyes of the birds, and an expert told us that for this reason most boobies die at sea when they become blind and disoriented after one too many dives!

Magnificent Frigates hanging in the wind. Half Moon Caye. Photo by Bob Thomas (while in his hammock). June 4, 2019.

But what we enjoy is watching the interactions (usually from our hammocks hanging from coconut trees) when frigates hang effortlessly in the winds, facing the sea, with a careful eye out for boobies returning to shore with a load of fresh fish to feed their young. This occurs to some extent all day long, but is most common late in the day. The boobies are well aware of the pirates (hence the nickname “man-o’-war bird”) sitting in wait, so they tend to fly low and rapidly in their attempts to reach their nests.  The frigates, however, dive down and acrobatically engage the boobies, harassing them repeatedly hoping the booby will drop its load of food. If they do, the frigate adroitly snatches it from midair – mission accomplished. If that first line of attack is not bad enough, there are usually a number of frigates hovering around the shared nesting sites for a second onslaught by hungry birds.  

Both photos above by Frank Jordan. Magnificent Frigate (left) and Red-footed Booby (right). Half Moon Caye. June 2019.

Happily for the frigates, this is a successful way to feed – called kleptoparasitism, or parasitizing boobies by stealing their hard-earned food with much less effort than finding their own. Happily for the boobies, their rapid runs through the frigate gauntlet are successful enough for them and their nestlings to have a good percentage of survival. And, happily for tropical biologists, that this is yet another excellent example to observe of behavioral approaches to resource acquisition.

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