2015 Fiji Islands Canopy Surveys
Assessment of epiphytic breeding site usage by Fijian Banded Iguanas (Brachylophus sp.)
Report submitted by Kim Lovich, Robert Fisher, Jone Niukula, Nunia Thomas, and Adam Clause
Fijian Iguanas (Brachylophus sp.) live in rain forests, mostly arboreal, and lay their eggs in small soil deposits in the forest. When they come to the ground during egg laying they are exposed to predation risk from invasive non-native mammals. The two largest islands in Fiji (Viti Levu and Vanua Levu) comprise about 85% of the land mass and iguanas are extremely difficult to detect on these islands. The few recent records for Viti Levu are from very good patches of primary forest, and observations have been tied to logging tracts, sometimes while logging is occurring. There were no recent records for Vanua Levu Island. How Fijian Iguanas persist with mongoose on these islands has been an important question. We hypothesized that perhaps iguanas can find suitable egg laying sites above ground and avoid predation risk. It’s possible they are utilizing soil that is captured in leaf baskets of the basket ferns (Drynaria sp.) high up in the tree canopy. The objectives of this project were: 1) to find any recent records for iguanas on Vanua Levu Island, and 2) to climb trees on Vanua Levu and Viti Levu Islands in forest patches were iguana detections were confirmed, to determine if they are utilizing any elevated soil habitats, particularly in these ferns.
During June and July 2015, we conducted a two-week expedition across Vanua Levu Island to identify the priority sites for attempting to find iguanas in trees. We drove across the island searching for good iguana habitat and interviewed villagers about the lizards. The island is about 170 km long, and we drove about 750 km over these two weeks. In 2014, we had previously surveyed the far western portion of Vanua Levu with IIF funding, so we did not revisit that section. The goal was to find recent reliable iguana sightings, as the only museum specimen from the island was from the 1800s. Once we found suitable habitats, we then conducted night surveys to search for iguanas and to further refine potential climbing locations.
One thing we saw in the canopy during our night surveys of Vanua Levu was an abundance of rats. This was surprising because on Viti Levu, and most other islands, you typically do not see so many rats in the canopy during night surveys. At the last survey area (Drawa Forest tract), we met with the village to discuss our goals and survey needs, as we did everywhere we travelled. We reviewed photos of various native reptile species to get a sense of how well the villagers knew the fauna. In Drawa, the locals showed us an amazing new species of skink (Emoia sp.) that was not in our field guide and occurred on trees around the village! We also found another skink in this village which had not been seen in Vanua Levu since its discovery in 1996, living on some of these same trees.
For our interviews, we focused on villages around good forest patches and also visited logging camps. Our interviews identified several places where people had seen iguanas historically, and those sites were also independently verified by loggers. Unfortunately, all of those sightings were from the late 1980s to early 1990s, and none recently. Fortunately, one hunter we met had collected an iguana last year in the Nabou Forest area. He brought the iguana to his village and kept it as a pet for several months. This iguana was independently confirmed by several other people that saw it, but no photos exist. We consider this record to be highly reliable. Although we found areas that seemed like suitable habitat, we did not detect any iguanas.
During December 2015, we conducted a two-week expedition that focused on climbing trees in areas with the most reliable iguana records from our previous field visits and interviews — one week each on Vanua Levu and Viti Levu. We used a single-rope climbing technique on the RAD (Rapid Ascent and Descent) system to access the canopy. Trees were selected based on size and presence of 1–3 searchable large clumps of epiphytes. Additionally, we were able to search four large trees for any evidence of iguanas (adults, eggs, etc.) that were freshly felled by loggers. We were unable to detect any sign of iguanas, even though we searched the epiphytes extensively. Unfortunately, we also detected rats and their tunnels in the epiphytes. This was quite surprising as these forest patches were pretty isolated from villages and the epiphytes were high in the trees.
Between two forest patches on the two islands we detected 16 species of reptiles and amphibians, representing about 60% of the known species from Fiji. This included a Fiji Barred Treeskink (Emoia trossula); a first record in at least 100 years for Vanua Levu as it was thought to be extinct on both large islands due to predation by mongoose. The skink we found was 16 meters high in an epiphytic fern, indicating this species is persisting as a canopy species in the presences of predators, whereas elsewhere it is commonly found low on trees or the ground. Overall, the canopy ferns did not contain the soil levels we had anticipated when we initiated this project, so we are still uncertain how to detect iguanas apparently still existing in small numbers in the mature canopy forest.
In summary, we have three places where we feel certain iguanas still persist in old growth forest on Viti Levu, but we were only able to find one place in Vanua Levu after an intensive 2-week expedition around the island (the pet noted above). We found no evidence of iguanas being reported in any areas that were exposed to wholesale logging, or in secondary forest. Only places that were “sustainably logged”, using best management practices, were possibly occupied still. These areas still maintain some canopy trees even though others are selectively taken. To build in-country capacity, we trained 19 people from various government, NGO, and university positions in Fiji on the techniques for rope-aided canopy access. We helped the University of the South Pacific (USP) acquire a climbing equipment set, so that they can continue to work with us in Fiji to survey for iguanas and other species in the tree canopy.
Future. We intend to continue exploring ways to detect iguanas in the primary forest on the major islands. We are considering the possibility of training dogs to find iguana eggs and nests, and at least confirm their presence in forest patches. Dogs might be able to specifically determine where an iguana is, and we can then follow up with canopy climbing to locate them in the trees. Without some way to refine and localize our search efforts, determining presence in the larger forest landscape is untenable currently. If future epiphyte searches still do not result in finding iguanas, it is possible they are using tree holes to nest like monitor lizards. If not holes, we can only assume they are continuing to come down to the ground for egg laying. This ground exposure must be what is limiting their numbers, in addition to the presence of rats in the canopy which was unexpected. We are very confident from the work on Monuriki Island that rats are major predators on iguana hatchlings. Possibly recruiting a student from USP to really focus on this question will be the best way forward.
The trip to Vanua Levu was very informative, but also quite startling. The paved road across the top of the island was now almost completed — foreboding that trade, logging, and mining will greatly increase, and thus the search for the iguanas on this island becomes more urgent.