The Cattle Egret: Hawaii’s Beautiful Invader

18 Aug

Most serious birdwatchers (myself included) will never forget the first time they saw a Cattle Egret in flight: they glide effortlessly at relatively low speeds with just a few economical strokes of their large and powerful wings, taking off and landing quickly with the grace and maneuverability of a light bomber plane. I saw my first egrets on the tidal flats of the east shore of San Francisco Bay near Alameda Island where I raced my sailboat as a teen. I never knew a bird so large could be so bright white!

Cattle Egret

A foraging Cattle Egret (Bubulcus ibis) poses for the camera without loosing track of its intended meal.
(Click on image for a larger version.)

Traveling and living abroad in later life, I saw them striding calmly among the tourists on the beaches of Caribbean islands, foraging in the salt marshes and tidal flats of the Red Sea’s eastern shores, roosting in the acacia trees and on the kopjes of the Serengeti Plain of Tanzania, striding hesitantly along the muddy shorelines of cattle ponds in Colorado, and hunting for bugs in the paths of groundskeepers’ gas-powered riding mowers on the newly-shorn lawns of Maui’s vast golf courses.

Cattle Egret

A bird in a hurry: a mature egret displaying breeding plumage.
(Click on image for a larger version.)

As a photographer, I’ve grown to appreciate this bird’s other attributes: it’s a large, bright-white bird with contrasting orange beak and legs, with its patches of caramel-brown breeding plumage, and its willingness to pose fearlessly for the cameras of appreciative humans. With so many of these photogenic birds on Maui and the neighbor islands, it’s hard to keep their snaps out of one’s photo gallery.

Cattle Egret

Cattle Egrets pick up a free meal by following landscape technicians wielding power mowers and hedge clippers, picking off wounded and stunned insects in their wake.
(Click on image for a larger version.)

Cattle Egret

A Cattle Egret doggedly searching for its next meal atop a freshly-trimmed hedge.
(Click on image for a larger version.)

So… here’s some stuff I read online about the species and some stuff I’ve learned by watching Maui’s own Cattle Egrets.

Interesting Stuff I Read Online

The Cattle Egret (Bubulcus ibis) is a member of the family Ardeidae (herons). B. ibis is the ONLY species in the monotypic genus Bubulcus. Not sure WHY there’s just one species of Bubulcus: either all the other species left town, joined other genii, or some slacker taxonomist got bored after naming just one species to this understaffed genus. Only in the field of taxonomy do you find a category with just a single item to populate it.

Cattle Egret

A mature adult Cattle Egret stalking insects as it lightly strides atop a Mountain Apple hedge in Wailea.
(Click on image for a larger version.)

This stocky, substantial-looking bird has a wingspan of nearly 40 inches (~100 cm). With its relatively short, thick neck and characteristic hunched posture, it stands about 25 inches tall (65 cm). It weighs only a bit more than one pound (~510 g). Its plumage is usually pure white, but during the breeding season, adult birds display prominent light-brown, caramel-colored patches on the neck and back (what I’ve seen on Maui); its legs and bill also turn bright orange. The irises of the bird’s eyes reportedly turn bright red as well, but I have never witnessed this on any in-season birds on Maui (see my photos). Immature birds share the white plumage of adults, but sport no mating plumage, although they do have a distinctive black bill.

This bird’s habitation range extends from the tropics and subtropics to the warm temperate zone. Because young birds tend to disperse thousands of miles from breeding and nesting grounds, and because adult populations may range from being wholly migratory to passage-migrant to wholly resident, this species has a geographically large range: approximately 10 million square kilometers (3.8 million square miles). Its global population is estimated to be between 3.5 and 6.5 million. For these reasons, the Cattle Egret is not considered an endangered or threatened species. Quite the contrary: the rapid expansion and establishment of the species over such a large global range has led to its official classification as an “invasive” species.

The Cattle Egret was first introduced to Hawaii in 1959. It is popular with cattle ranchers throughout the world for its role as a biological control of ticks, biting flies, and other cattle parasites, pecking the little nasties directly off the skin of stock animals. It was this perceived benefit to livestock that prompted local ranchers (with the help and blessing of the Hawaiian Board of Agriculture and Forestry) to release the species in Hawaii.

Stuff I Learned Watching Birds In The Field

I live in Kalepolepu, a quiet residential neighborhood in north Kihei. A lot of the small beachfront homes have good-sized lawns with fast-growing grasses, and the nearby beaches are covered with ‘Aki ‘aki grass (a tough variety of buffalo grass). Small lagoons, cut-off ponds of brackish water, and other artificial and natural wetlands dot the neighborhood. All of which makes an ideal habitat for legions of terrestrial insects, frogs, toads, lizards, and small freshwater fish… the main dishes on our cattle egrets’ collective menu. From early spring until late summer/early fall, large numbers of migratory egrets follow behind homeowners and landscape technicians riding their self-propelled lawnmowers, picking off grasshoppers and other lawn-loving insects wounded and stunned by the mowers’ blades. When that first course of the moveable feast is done, the birds fly off to the wetlands, ponds, and garden pools to nab toad and frog tadpoles, as well as mullet and other small bait fish that flourish year-round in their warm, well-aerated water.

At least on Maui, Cattle Egrets don’t spend much time foraging on beaches or in the intertidal zone. In 10 years I have only seen two egrets flying over the open water of Ma’alaea Bay (see my photo, below). For a species that is known to migrate vast distances over open ocean, Cattle Egrets don’t seem to regard the marine environment as anything but a barrier to be overcome on the way to their next meal on terra firma.

Cattle Egret Flying

A rare bird, indeed: a solitary Cattle Egret struggles against a stiff headwind while crossing the open water of Ma’alaea Bay.

B. ibis has a reputation elsewhere in the world as a predator of other bird species: they eat the chicks and eggs of other shorebirds; they kill and eat other species of land birds exhausted from migration; and they chase the chicks of some species of terns, forcing them to disgorge their food. I’ve never witnessed this behavior or heard reports of it on Maui or the other neighbor islands. This may be because there is such an abundance of insect and reptile prey species that is readily obtainable without much of an expenditure of energy on the egrets’ part.

I believe the egrets come to Maui for the same reasons as all the other tourists: the weather’s warm and mild most of the year, and there’s plenty of places on the island to get a tasty meal and a good night’s sleep. So the human and bird tourists all agree: Maui na oka oi …”Maui is number one!” No argument there.

I gotta phase… Laters!

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4 Responses to “The Cattle Egret: Hawaii’s Beautiful Invader”

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