'Devil birds' moving in at Lake Merced Biology

Several Great-Tailed Grackles perch in a tree at the Southern end of Lake Merced on Wednesday Nov. 21, 2012, in San Francisco, Calif. The mysterious flying aliens known as Devil Birds have been spotted in San Francisco's Lake Merced. The Great-Tailed Grackle has expanded its breeding range into the San Francisco Bay Area. less Several Great-Tailed Grackles perch in a tree at the Southern end of Lake Merced on Wednesday Nov. 21, 2012, in San Francisco, Calif. The mysterious flying aliens known as Devil Birds have been spotted in San ... more Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 5 Caption Close 'Devil birds' moving in at Lake Merced 1 / 5 Back to Gallery

A gang of cantankerous flying aliens known to some avian aficionados as "devil birds" have been spotted flitting around San Francisco's Lake Merced acting like they belong.

The crow-sized creatures, which ornithologists know as great-tailed grackles, are native to Latin America and the southern United States, but the aggressive birds have recently been moving west, gobbling up the eggs of other birds and threatening to make a nuisance of themselves.

As many as six males and two females have been seen at Lake Merced, the largest concentration of the species ever recorded in San Francisco, according to the experts.

"They are often vilified as devil birds," said David Cruz, a local photographer and founder of Natures Lantern, a local nature photo and video sharing site. "It is a unique bird that many San Francisco residents have yet to see."

The birds, known scientifically as Quiscalus mexicanus, have in recent decades expanded their range from Texas and parts south of there to Northern California, most likely because of human-caused changes in their habitat. The first sighting in California was along the Colorado River in 1964. The birds have since colonized much of urban Southern California and parts of the San Joaquin Valley.

Great-tailed grackles have been seen in the Bay Area before. A pair of them gained fame in 1986 when they dive-bombed workers attempting to cut down their nesting tree. The birds, affectionately named Jose and Rosalie, first showed up in the late 1970s, but could not establish a nest and eventually disappeared, said Joseph Morlan, an ornithology instructor at City College of San Francisco.

Many local birders are secretly hoping the latest gaggle of grackles will have better luck.

"It's a big deal in the sense that few other birds have spread in North America so aggressively," said Morlan, one of the foremost birders in California. He said only the Eurasian collared dove has spread across the country more rapidly.

Great-tailed grackles are lowland species, which favor lakes and marshes and like to nest over or near water. The males are black with a violet-blue iridescence and can grow 17 inches long. The females grow to about 13 inches and are mostly brown.

The gregarious birds are sometimes considered pests because they thrive around humans, raiding crops and poaching tidbits. The Aquatic Park duo lived on french fries offered by the owner of a local fast-food stand. To the dismay of those who live around them, the birds like to gather together before dawn and after sunset for little concerts, producing a sound that one ornithologist said was less melody than a cacophony of "otherworldly shrieks."

The color, smarts and brazen attitude of great-tailed grackles have led to many myths about their supernatural qualities, poisonous beaks and evil eyes. The real threat, however, is more to other birds than to people.

"They also (prey on) the nests of other birds and if nesting at Lake Merced in large numbers may have an impact on other marsh nesting species," said Morlan, the co-author of "Birds of San Francisco and the Bay Area" and "Birds of Northern California." "They are known to eat eggs and nestlings of other species and occasionally eggs of other individuals within the colony."

Morlan said there is little that can, or should, be done to stop the birds from establishing a resident colony in San Francisco.

"They are simply adapting to changes in the environment," he said. "Ultimately all life must adapt to these changes if they are to succeed. It's called natural selection. Changes in range and adapting to changes in environment like these are powerful examples of evolution in action."