19 November 2009

Yesterday on our way out to the end of Tranberg Rd. (a.k.a., Refuge road) we stopped to chat with Sharon Grimes, a local naturalist who was conducting turtle surveys several times each week for Claudia Lombard while she is participating in one of life's most fundamental and oldest processes - her first child is due in several weeks. Claudia is also busy with an exotic vegetation eradication project on Green Cay. According to Mike Evans, Green Cay is home to only one of several small populations of the St. Croix ground lizard. Many blame the mongoose for the extirpation of the St. Croix ground lizard from St. Croix and other locations in the Caribbean, but then mongoose are blamed for most everything bad that happens to native island populations. This reaction results primarily from correlative observations - mongoose were introduced to an island and then some time later species X declines. If life were only this simple, then we biologists would be out of a job. The equation contains many more variables and interactions among those variables than is often recognized. For example, rats have been introduced everywhere we humans have migrated since we left our African homeland. On Green Cay rats have altered the vegetative structure of the island by pruning new shoots and seedlings thus reducing the canopy cover of the native trees and shrubs allowing invasive grasses (e.g., Guinea grass) and shrubs to take over and reducing ground lizard habitat. The equation, at its bare minimum, must include rats, native vegetation, exotic vegetation, humans, ground lizards, and various forms of interactions among these variables. I left out mongoose, because there is no evidence that they have ever been present on Green Cay. All these variables plus some more and their interactions (e.g., native habitat destruction resulting from human disturbance - building roads and houses) must also be included in the St. Croix formula. I would never argue that mongoose have had no impact on ground lizards, sea turtles, nor ground nesting birds. However, I will argue that to claim that the mongoose is the only or even most important factor influencing the survival of these species is much too simplistic.

We captured two mongoose and a land crab in 25 traps. These numbers are similar to the success rate we experienced last November but much lower than previous trips. I have also not yet seen mongoose running across the road. We use the same trapping techniques that we always do, yet capture far fewer animals. This leads me to believe that the population is lower than it has been in the past. At this point in time I will reserve my speculations as to the cause of these differences to a later date.