Project Report: January 2004
Twenty-four headstarted iguanas (12 males and 12 females), with surgically implanted temperature-sensing radio-transmitters, were released on Anegada in October of 2003. Releases took place in early October, during the peak of the wet season, as food resources are most abundant at this time. Twelve iguanas, six from each sex and size class, were released in each of two habitats: coastal sand scrub in Windlass Bight (Faulkner site), and inland limestone woodland (Middle Cay site). Both habitats are centrally located within the remaining core iguana area and within the protected RAMSAR site.
The release was a big event on Anegada. The staff of the British Virgin Islands National Parks Trust (BVINPT), the Anegada District Officer, and local residents participated in the release. In attendance were members of the UK Foreign Commonwealth Office, the UK Dept. of International Development, and the BVI Governor's Office. The event was covered locally in the BVI newspapers; international coverage included CNN.com and the Associated Press.
After the initial release in October, the iguanas were manually tracked for the first three weeks. One animal was found dead on Middle Cay two days after the initial release, due to complications from the surgery. A receiver was left with Rondel Smith of the National Parks Trust so that he could continue to monitor the iguanas once a week.
The first follow up trip was in late November. Two weeks before this trip, Anegada experienced record rainfalls for November, and most of the island was flooded. This event is important for two reasons. First, the iguanas were able to survive in an extreme environmental condition. Second, the food sources were extremely abundant. The animals were again manually tracked for almost three weeks. A second mortality occurred due to unknown reasons, only the transmitter was recovered.
All the remaining animals were recaptured, weighed, and measured. The lizards from the Middle Cay release site gained significantly more weight than the animals from the Faulkner release site. A decrease in weight was recorded in four individuals, all from the Faulkner release site.
The suture sites on all the remaining iguanas have healed completely. Ticks were found on all the animals from the Middle Cay site, but were completely absent from the Faulkner group. The number of ticks and attachment sites were recorded for each animal.
Animal locations were recorded every other day with a GPS. There was not a significant difference in the distance moved between the two locations. The shortest and longest distances moved by animals on Middle Cay are 13.01m and 390.58m. The same distances for the Faulkner site are 22.34m and 322.00m.The farthest distance one animal has moved in a single 24-hour period is 286m.
All the iguanas appear to have established a rough home range. One interesting note is that the largest male and the smallest female on Middle Cay are most often found together, within one meter of each other. Many of the iguanas appear to be demonstrating retreat site fidelity. Many animals at the Faulkner site are using deadwood piles along the fence line as retreats. However one male has dug a burrow and is repeatedly seen using it. Most of the animals on Middle Cay are using rock crevices.
The RX900 unit has collected a vast amount of data on the released iguanas. The unit is constantly, spending one minute on each individual frequency. The unit completes a scanning cycle every 22 minutes. Each time a frequency is detected, the unit records:
- Which group of antennas picked it up (left or right)- gives some directional information
- the strength of the signal - gives some distance information
- the pulse period - gives internal body temperature
- the time and date
The remote antenna station easily picks up the animals released in the coastal sandy scrub area. Many of the animals on Middle Cay are detected, but not as often as the coastal group. A preliminary analysis of the temperature data shows that these animals get up to 40 °C (104 °F) and as low as 23.3 °C (74 °F).
Focal animal observations for behavior data are being conducted to determine if the iguanas are exhibiting natural behaviors and can adapt to living in the wild after spending the first 4-6 years of their life in captivity. Focal observations are conducted between 0830 and 1640. I am making notes on diet, habitat use, activity periods, and interactions with wild adults and other released iguanas. This data will ultimately be used to construct energy budgets for the released iguanas.
We plan to replicate the project again in 2004 and 2005. The ISG is currently proposing to add a third and smaller size class to the group to be released later this year. Incrementally decreasing the size of headstarted animals released in this way will allow us to determine the optimum size for release over time. The animals released in 2003 will continue to be tracked and monitored periodically.