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Extended Entries to the ASDM Scrapbook

Saving the Birds of Isla Rasa

by Peggy Pickering Larson

One of the world's densest avian nesting populations would have been irreparably lost in the 1960's had it not been for a small number of U. S. and Mexican conservationists, a concerned benefactor, and the President of Mexico. It was one man, however, who originally recognized the threat to the birds, publicized it, and drew together the individuals and forces that ultimately resulted in Isla Rasa, the nesting site of the birds, being officially declared the first Migratory Waterfowl Sanctuary in the Sea of Cortez. That man was Lewis Wayne Walker, ornithologist, photographer, author, and Associate Director of the Arizona-Sonora Desert Museum from 1954 through 1970.

Isla Rasa lies approximately 400 miles south of the head of the Sea of Cortez. The island is less than a square mile in extent and at its highest point not quite 100 feet above sea level. Yet three bird species, totaling more than a million individuals, nest there annually. Heermann's gulls migrate from California's coast and from as far south as Panama to reach Isla Rasa by April first. They arrive in dense flocks, pick out their tiny plots, and almost immediately lay eggs. Soon the valleys' floors are covered with incubating gulls. About ten days later Elegant and Royal terns arrive, migrating from the California coast and from as far south as Central and South America. They linger in the tidal lagoons and each day their numbers increase. The birds grow restless and flocks of thousands rise, swoop low over the valleys, and return screaming to the lagoons.

A night comes when a tern flock numbering thousands of individuals descends on land already claimed by the gulls. Through sheer numbers they dispossess the gulls and start laying their own eggs. At dawn the terns control a plot perhaps fifty feet in diameter, with the evicted gulls circling the new colony and robbing any unprotected tern eggs on the periphery. Due to predation, the colony shrinks, but with darkness additional terns arrive and the colony expands.

Shrinkage and expansion continue. By the time growth stops, the first eggs laid-now in the center of an acre or two of terns-begin to hatch. The precocious young band together, move through those that are still incubating, and hide in the rocks where they are miraculously found and cared for by their parents. The hollow center of the colony is invaded by predaceous gulls.

Gull nests occur just 18 inches apart, while tern nests are separated by a mere 8 to 9 inches. Lew Walker reported that when he first visited Isla Rasa there were eight tern colonies, each occupying approximately one to two acres, these totally surrounded by masses of gulls. Isla Rasa is the primary nesting area for both Royal and Elegant terns and the island is the main breeding location for the Heermann's gull. It is estimated that Gulf of California islands, primarily Isla Rasa, provide nesting habitat for 90 per cent of the North American populations of these three species.

Lew Walker began exploring Baja California and the Sea of Cortez in the late 1930's, but his trips were suspended while he served as a Marine in the Pacific. Upon his return he resumed his travels. At that time roads in Baja were dirt tracks and the waters of the Gulf little known except by Mexican fishermen. Lew wrote of one of his earliest trips in the Gulf, "We went for seven weeks without seeing another boat."

He first visited Isla Rasa in 1946. In Bahia de Los Angeles he hired a boat "homemade from flotsam of the Gulf" and its turtle-fishing owners to take him to Isla Rasa. The boat, powered by currents, oars, and a sail full of holes, arrived at the island a day and a half later. The masses of birds thrilled Lew. Upon his return to the U. S. he sold an article and photographs, "Sea Birds of Isla Raza," to National Geographic Magazine. In 1947 he returned to the island and to his amazement found very few nesting birds. Their absence was a puzzle, but a clue was present, "Human footprints were plainly evident where they had not been erased by the winds."

In 1948 Lew attempted to return to Isla Rasa, but when approximately ten miles from the island, a storm blew up, and his party took shelter at Isla Cardonosa. During the night their small boat sank in 15 feet of water, immersing cameras, film, and motor. They managed to raise the boat, and after three days were successful in getting the motor running. They watched flocks of birds heading to Isla Rasa but could not reach the island, and were fortunate to finally return to Bahia de Los Angeles.

The 1947 footprints were later explained when Lew met a Mexican fisherman who reported that motor-equipped boats had visited Isla Rasa earlier that year and removed thousands of eggs to be sold for food in Santa Rosalia and other ports. Some minor egging had been conducted in other years, but as transportation became easier and markets grew, annually the eggers increased in number. Men invaded the island during the nesting season, relentlessly sweeping up the eggs, which were tested in buckets of salt water. Eggs that floated were partially incubated and thrown away. Those that sank were fresh and carefully packed to be sold for food in nearby ports.

As Lew returned to Isla Rasa year after year, he documented the astounding decrease in the bird population in direct ratio to the increase in human marauders. There were years when reproduction, which should have been close to a million, was cut to several thousand. Isla Rasa's days were numbered. Lew shifted into high gear.

Dr. Joseph Wood Krutch was a Desert Museum Trustee and Lew's good friend. A San Francisco industrialist and Board member of the California Academy of Sciences, Kenneth Bechtel, admired Dr. Krutch's natural history books and contacted him. Their friendship grew and Bechtel's plane took Krutch, Walker, Arizona-Sonora Desert Museum Director William H. Woodin, and others to Baja California numerous times where the group studied the need for research and conservation. Bechtel established the Belvedere Scientific Fund with Krutch, Walker, Woodin, and well-known scientists named to the board. Lew sought the help of Roger Tory Peterson, renowned ornithologist, author, artist, and an administrator with the National Audubon Society, Dr. George Lindsay of the California Academy of Sciences, and Carl Buchheister, President of the National Audubon Society. In 1961 Peterson, Krutch, Walker, and Mervin Larson from ASDM spent a week on the island producing a film which was widely shown. The desperate need for protection of the birds of Isla Rasa was made known to Mexican scientists in positions of authority.

I n 1964 the deteriorating situation on Isla Rasa was made impressively apparent when Carl Buchheister, under the auspices of the Belvedere Scientific Fund, surveyed the Isla Rasa bird population. In April he found 21 men encamped on the island, seven boats anchored nearby, and expectation on the part of the eggers to take approximately 400,000 eggs. Buchheister wrote, "In short, these men were removing all eggs as fast as they were being laid, and from the entire island." Not a single chick was to be found. He called it, "One of the most shocking acts of human predation on wildlife that I have ever witnessed." Buchheister returned in June and found that some of the terns had been able to nest a second time with limited reproduction, but he estimated that the nesting and reproduction of the Heermann's gulls for that season was a 99 percent failure!

The conservation interests of the National Audubon Society focused on the tiny island. The Belvedere Scientific Fund sponsored scientific expeditions to the Gulf. It provided funds for biological investigation and later for enforcement of protective regulations. The Arizona-Sonora Desert Museum actively supported the conservation efforts being made. In Mexico Dr. Enrique Beltran, subsecretary of Forestry and Game, and Dr. Rodolfo Hernandez Corzo, Director General of Wildlife, became personally and professionally involved in the project. At last, on May 30, 1964, President Lopez Mateos signed a decree which established Isla Rasa as a Migratory Waterfowl Sanctuary, a move that would ultimately lead to protection of all the islands in the Sea of Cortez.

William H. Carr, Director Emeritus of ASDM, praised Walker, "Lew's successful efforts to interest people in the establishment of the Republic of Mexico's first bird sanctuary on the island of Raza in the Gulf of California, will always remain as a leading accomplishment in the field of wildlife conservation."

Lew's wife, Melanie, stated. "Lew's proudest achievement was the role he played in the creation of this sanctuary." After his death in 1971, Lew's ashes were scattered over the Isla Rasa wildlife sanctuary he loved and was instrumental in establishing.

Retrieved from the Arizona-Sonora Desert Museum web site on 07-24-2024