The next installment of Dr Justin Gerlach’s important work to save one of the world’s most threatened bat species.
Conservation in the Seychelles islands faces the same issues as almost any other small island group – development, population fragmentation, invasive species and climate change. The islands were not settled until 1772 so we have had only a short history of human disturbance. Impacts must have been severe in the early 1800s when over 99% of lowland forests were cut down for the establishment of coconut plantations. What disappeared in those times will probably always remain unknown as the first visits by biologists did not occur until the middle of the 1800s. The Seychelles sheath-tailed bat was one of the species discovered by those early visits, being described in 1869.
Invasive species followed the first explorers and settlers and now rats and cats are well established on almost every island. Invasive plants made their appearance with the creation of plantations, escaped spices now create havoc throughout the islands. Cinnamon is the most obvious problem species, along with timber trees, weeds and coconuts. The latter species should be growing only along the beaches but were planted to 400m above sea level, these now dominate many areas, forcing out many of the endemic plants and associated animals.
Development has only relatively recently been a significant conservation issue in Seychelles. Currently there is a great expansion in housing and in hotel building, often in previously isolated areas. Dealing with economics and social issues is a new experience for most conservationists in Seychelles. We also know very little about the effects of population fragmentation in the islands. With the sheath-tailed bat all known colonies number 1-32 bats, so they are clearly very seriously fragmented. Our first priority must be to stabilise populations and encourage them to increase again.
Within the roosts that are still occupied we have tried to monitor the number of bats present. The main roost on Silhouette, the La Passe roost, usually contains several dense clusters of bats. Determining how many bats are in those clusters is almost impossible. Many hours have been spent watching them, counting and re-counting. Often a group will be counted and will then move, as the bat move you realise that what you took to be one bat is actually three. By the time you have realised this the other bats have regrouped and the count is confused again. Only by hours of patient observation have we been able to chance on the times when the bats spread out and reveal their true numbers. In 2006 we installed a CCTV camera in the roost. This now enables us to observe and record their behaviour and make much more accurate counts. This has given us many new insights into their lives although we still have technical problems with the infra-red part of the system that is supposed to reveal their night-time activity in the roost. If all goes well we should be able to sort this out in the next few weeks. This will be an exciting season for research on this species as it has been speculated that they have a breeding season in April in addition to the main breeding season in December. With the camera working properly we may be able to prove that idea.
If you wish to find out more about Justin’s important work or support the conservation of this critically endangered species, please visit the Nature Protection Trust of Seychelles website or email Justin directly at JstGerlach@aol.com.