Research

Midriff Islands of the Sea of Cortés

Seri Indians call themselves the Comca’ac, and for centuries have lived along the coastal region northern Sonora, México, and on various eastern islands in the northern Sea of Cortés, such as Isla Tiburón and Isla San Esteban. For many years Dr. Gary Nabhan (Director of the Center for Sustainable Environments at Northern Arizona University) has studied the ethnobotany and ethnozoology of these people.The Comca’ac were hunters and gathers, living on the local biota such as the numerous sea turtles, island lizards, and agave plants. Although the modern climate, faunal communities, and floral communities have been studied at length, what is not understood is the recent past – those climates and environments that lead to the present system.

There are many unusual plants and animals that are endemic to the various islands in the Sea of Cortés. The San Esteban Island chuckwalla lizard (Sauromalus varius) is found on only a few of the islands, as is the spiny chuckwalla (S. hispidus) and the spiny-tailed iguana (Ctenosaura conspicuosa). When did they arrive there? Were they always there or were they introduced to the island by the Comca’ac? Is it possible that some of the islands had a pre-human population of unusual and endemic animals that soon became extinct due to over-exploitation by the arriving humans? Have the Comca’ac transplanted select species of lizards to some islands as a food resource in reserve.

Isla Tiburón is separated from the mainland at Bahía Kino by just a few kilometers of shallow water. During the Ice Age when sea water was locked up in glaciers covering the high elevations of major mountains worldwide, much of Canada and northern USA, and northwestern Europe, sea level was lowered over 120 m. Isla Tiburón was then a peninsula jutting out into the gulf.

South and west of Isla Tiburón is the small island of Isla San Esteban. Separated today from Isla Tiburón by about 18 km and water reaching 265 fathoms deep, Isla San Esteban has been remote for tens of thousands of years, possibly since the end of the Pliocene at about two million years ago. The present fauna of Isla San Esteban is significantly different from that of Isla Tiburón. How and when did this insular fauna evolve?

In January 2001, Gary Nabhan, Lori Monti, Sandy Swift, and Jim Mead visited Isla San Esteban and Isla Tiburón to assess the possibility of recovering a sub-fossil and fossil record of the amphibian, reptile, bird, and mammal history of the islands. With the aid of the Comca’ac and their pangas (boats), the crew visited various areas to look for caves and rock shelters that could preserve a record of past communities.

One shelter produced an exciting deposit of owl pellets. Although only the burrowing owl is recorded from the island today, the pellets have the distinct characterization of being produced by the barn owl (Tyto alba; not recorded from Isla San Esteban but known from Isla Tiburón). The random test sampling produced pellets from obviously modern roosting in the cave, but some pellets were highly degraded and the bone appearing ‘much older’; there is evidence of some depth in the deposit. The pellets contain a wealth of skeletal data.

The European-introduced rat (Rattus) was found only on the surface, and only as a rare occurrence. The pellets were dominated with bones from the chuckwalla, spiny iguana, birds (including the non-local elf owl, Micrathene whitneyi), and bats (including the unusual fishing bat, Myotis vivesi). The cave and its deposits illustrate that a tremendously interesting subfossil (and hopefully fossil) record exists on Isla San Esteban.

In December 2005, QSP student Caitilin Mccraken accompanied Dr. Nabhan to the Seri villages of Punta Chueca and Desemboque and participated in a number of activities with the Seri. The chuckwalla captive breeding exhibit in Punta Chueca was of particular interest to Caitilin, since her Master's thesis is a study of the cranial morphology of the common chuckwalla lizard (Sauromalus ater) of the Mohave and Sonoran deserts. The San Esteban Chuckwalla or Painted Chuckwalla (Sauromalus varius) is endemic to Islas San Esteban, Lobos and Pelicanos and are deserving of special protection. The exhibit encourages the Seri community to remain involved in the protection and celebration of its reptilian neighbors. The captive breeding has been a great success and had reached its maximum holding capacity. Therefore, Dr. Nabhan, Cailtilin and the Seri participated in the organization, removal, and relocation of two chuckwallas from the exhibit.

The Seri village of Desemboque, Sonora, Mexico.

Guadalupe, one of the last and most talented sea turtle hunters. "Lupe" was instrumental to learning about the ethnozoology — an encyclopedia of information.

Agaves were harvested on Isla San Esteban and brought back for use in Punto Chueco.

The chuckwalla, Sauromalus varius, on a rock near the beach line on Isla San Esteban.

A view west from Sargento, near Desemboque, to Isla Tiburón. The large columnar cactus, cardon, (Pachycereus pringlei) are common.

QSP student Caitilin McCracken aided in the removal of a chuckwalla from the Seri exhibit