2012 IIF Grant Report and photos submitted by Tarren Wagener and Glenn Gerber
Background. The Turks and Caicos Iguana, Cyclura carinata, is listed as Critically Endangered on the IUCN Red List of Threatened Species due to introduced mammals and habitat alteration. Inter-island translocations have been a key conservation strategy for the species. Six inter-island translocations have been conducted to date (four using iguanas from Big Ambergris) and all have been successful. However, additional islands suitable for translocation (good habitat, protected, and free of mammals) are now scarce despite a surplus of animals threatened. Consequently, intra-island translocation strategies that complement human needs must be found. Big Ambergris Cay supports the largest remaining population of Turks and Caicos Iguanas, and presents a unique opportunity to determine the effectiveness of intra-island translocations while also mitigating specific threats facing the island’s iguana population. Fortunately, many of the recommendations concerning iguanas set out in the Big Ambergris Cay Strategic Environmental Impact Assessment have been adopted, including small building footprints, use of low speed golf carts, dirt roads, and most importantly, a restrictive covenant that forbids anyone from bringing cats, dogs, or other pets to the island. As a consequence, Big Ambergris is the first island to be developed in the Turks and Caicos Islands (TCI) that stands a chance of preserving its iguana population. The goal of this project is to establish a successful intra-island translocation program that can be used to mitigate the impacts of human development on the iguanas. This goal will be accomplished by determining translocation effectiveness on Big Ambergris by age (adult versus juvenile), sex (male versus female), and season (dry/pre-reproductive versus wet/non-reproductive). A secondary objective is to document homing behavior and post-translocation stress levels in the Turks and Caicos Iguana as these factors could negatively impact translocation efforts on island.
Methods. In April 2011, two study sites were chosen for the project duration. Study sites were assessed for relative iguana abundance through systematically-timed surveys during which the number of iguanas encountered were recorded and estimated by sex and age class. In addition, a survey of the plant species present at each site was conducted. The two study sites were both composed of karst habitat with cactus-scrub vegetation. The first study site was the loyalist “ruins” and the second the “tents.” At both study sites, there is a road that bisects the core area, and they are both located on the same side of the island, to the east of mid-line. They are located approximately 0.8 km apart and are oriented north and south of each other.
In each of the field seasons (Fall 2011 and 2012), 12 individuals were captured and processed at each site (3 adult males, 3 adult females, and 3 juveniles), for a total of 48 individuals across both sites. Subjects were captured with a noose pole, bled for stress analyses, weighed, measured, sexed, assessed for body condition, and individually marked with a unique bead tag sequence attached to the dorsal crest and a PIT tag placed sub-dermally on the proximal dorsal surface of the left rear leg. All subjects were also outfitted with externally-attached radio transmitters (Holohil Systems, Ltd. Model BD-2 (1.2 g) using 5200 marine caulk on the lateral surface of the tail base immediately behind the left rear leg. All subjects were released at their point of capture within 24 hours of processing. Following release, all individuals were located at least twice daily for 14 days, with hours of tracking standardized to ensure an even distribution over the active hours of the subjects. A Trimble GeoExplorer handheld datalogging GPS (Global Positioning System) was used to record iguana locations, along with animal ID, date, time, habitat, and behavior notes. After 14 days of tracking, subjects were recaptured, bled, weighed, measured, and translocated to the alternate study site, that is, from the ruins to the tents and vice versa in an effort to control for social density effects. For example, when the three adult males from the ruins were translocated to the tents, three adult males from the tents were translocated to the ruins. In sum, there was a net gain of zero adult males at each study site. Following translocation, all individuals were located at least once daily, and most often twice, every 1.5 days. At the end of 14 days, all animals were recaptured, transmitters were removed, and animals were released at their capture location.
Movement and Behavior. More than 1,200 locations were recorded across the baseline movement portion of the study for all subjects. Each subject had at least 24 locations during this period. Apart from one male at one study site that displayed wide-ranging movements, all animals displayed limited and consistent movement patterns throughout the baseline study period. During the translocation period, there was a total of more than 830 locations collected across all animals, and at least 15 locations per individual.
2011 — Five of 12 adult iguanas (3 males and 2 females) homed back and were located using the exact retreats identified in the first portion of the study. Two males and one female homed from the ruins to the tents, and one male and one female homed from the tents to the ruins. From the release date, the shortest homing time was ~3 days; the longest was 15 days. There were also individual differences related to the onset of homing behavior. At least one individual left immediately and stayed true to a homing direction throughout. Other individuals remained at the translocation site for several days, and then departed. None of these individuals moved in any direction other than generally towards “home” or generally between “home” and the translocation spot.
Individuals that did not home, though moved, exhibited several strategies. Several individuals made multiple forays in the direction of home but returned in-between the forays to a “home base” at the translocation site. Forays would be of varying distances and times (including overnights), but most often in the general direction of home. Other individuals took off from the core area and established a “home base” that would slowly change further from the translocation area and towards home, without backtracking. One individual established a home base on top of the first ridge from the translocation site for more than ten days without moving. However, at the end of the study period, he moved towards the shoreline and back towards the translocation site, and was ultimately re-captured in the translocation study site.
Eight of the juveniles remained in the translocation site and seemed to be establishing home ranges at the end of the study period. Several individuals exhibited wider movements than the baseline movement period. One juvenile made multiple forays towards home, interchanged with returns to the translocation site as previously mentioned for some adults. This individual was last located nearly halfway towards home. Two other juveniles left the core study area as well. One of these did not make forays back and forth but did seem to be establishing a home range outside of the translocation site. As with the adults, no juveniles moved in a backwards direction from home, unless heading back to a translocation spot from a foray.
Many translocated animals chose the exact retreats of study subjects that had been removed and translocated to the alternate study site. This behavior was noted across all sexes and age classes. Several instances of social conflict were observed between returning residents that had homed back, and translocated individuals who had not left the translocation site. Several behavior notes for other individuals did include chasing by resident animals.
2012 — Four of twelve adults (3 females and 1 male) homed back and were located using the exact retreats identified in the first portion of the study. Three females homed from the ruins to the tents, and one male homed from the tents to the ruins. From the release date, the shortest homing time was six days; the longest was 17 days. There were also individual differences related to the onset of homing behavior. At least one individual left immediately, and other individuals remained at the translocation site for several days, then departed. One female at the tents never moved from the translocation site.
Moving individuals exhibited several strategies. Several individuals made multiple forays in the direction of home, but returned in-between the forays to a “home base” at the translocation site. Forays would be of varying distances and times (including overnights), but often in the general direction of home. Other individuals took off from the core area and ventured far off-course from the anticipated homing direction, returning repeatedly to the translocation site prior to attempting a foray in a different direction.
Eight of the juveniles remained in the translocation site and seemed to be establishing home ranges at the end of the study period. Two juveniles lost their transmitters. One was never translocated, and the other seemed to be establishing a home range at the translocation site prior to losing it. Several individuals exhibited wider movements than the baseline movement period. Two juveniles left their respective translocation site and ventured far from the site in the wrong direction from home, both traveling due east to the edge of the island. Only one of these was re-caught during the final capture period and the other was presumed dead from predation or lost the transmitter since nearly a week’s worth of locations indicated no movement.
As in 2011, several translocated animals chose the exact retreats of study subjects that had been removed and translocated to the alternate study site. This behavior was noted primarily for juveniles.
Stress Analyses. During each capture event, all subjects were bled for the stress analyses to determine corticosterone concentrations and leukocyte analysis via the ratio of blood heterophils to leukocytes. Adult animals were bled twice during each capture event. The first sample was taken within three minutes and is considered a baseline sample. The second sample was taken from 30 minutes to 1.5 hours following the first sample, representing a capture-stress reading. In 2011, juvenile animals were bled only once, representing a capture-stress sample. However, in 2012, juveniles were bled twice for both a baseline and capture-stress reading. All blood was kept on ice, and three slides were made from each sample within 1.5 hours of collection. All slides were air-dried, two fixed and a third stained with Wright-Giemsa stain. In 2011, 296 blood smears (produced in triplicate per sample) and 70 plasma samples for the corticosterone analysis were collected. In 2012, 288 blood smear and 112 plasma samples were imported. Analysis of these samples are on-going.
Next Steps. In late 2012 or early 2013, Principal Investigator Wagener will travel to San Diego to work with a GIS specialist and endocrinology department on analyses of all wet season datasets. Work is also underway to solidify dates for the spring 2013 field season (February/March). At that time, 24 adult and juvenile iguanas will be captured, processed, and outfitted with transmitters. All individuals will be located via radio-tracking and GPS at least twice daily for 14 days. At the end of this period, radio-tagged iguanas will be recaptured, bled, weighed, measured, translocated to an equivalent habitat (based on vegetation and iguana abundance) and radio-tracked for 14 more days. Following the second 14-day tracking period animals will be recaptured, have their transmitters removed and will be bled, weighed, measured, and released at their current capture location. The complete project will include four field seasons (2 dry and 2 wet seasons).
Personal communications with both Big Ambergris homeowners and the island manager indicate that plans are underway to begin development on the island again in 2013. These plans call for a hotel and separate bungalow area and will significantly increase threats to the iguana population on-island. Determining the utility of intra-island translocation during the early stages of this development is critical and will allow for an informed conservation strategy to be implemented as these development pressures increase. For example, it may be learned that adult females exhibit less of a homing tendency during the dry season compared to the wet season and that juveniles never exhibit a homing tendency; or, that adult males lose significant body condition and exhibit a large stress response (indicating reduced survivability) following a dry season translocation, but not during the wet season. In sum, these collective results will guide a proactive strategy to mitigate iguana losses from development on-island. By working with the Big Ambergris Cay development team, biologists can work to optimize timing and translocation methods for each construction event. It is also anticipated that the results of this project will extend far beyond Ambergris and the TCI, and will serve as a model for endangered rock iguanas throughout the Caribbean.