Galapagos tortoise movements on other islands
Some initial success led to increased funding for the Galapagos Tortoise Programme, and the movement study was extended to two other islands. The programme has now deployed 47 GPS tags onto tortoises from four different species on three different islands. These include the small flat, arid and hot island of Espanola to the southeast of the archipelago, Santa Cruz with its variety of lowlands, uplands and permanent human habitation including extensive farmland, and an urban area, and the majestic Alcedo volcano on Isabela Island which rises to 1100m above sea level and is among the most pristine areas of Galapagos. By tagging tortoises over a range of ecological and environmental conditions, the data will help resolve long standing questions about animal movement in general not just in Galapagos tortoises.
Weighing up to 300kg, giant tortoises are by far the largest terrestrial animals on Galapagos, some 10 times larger than the land iguana, the next largest animal. Very large animals such elephants and hippos are often collectively referred to as Megavertebrates. Due to their size, the megavertebrates often play particularly important ecological roles compared to smaller species, since they eat large quantities of vegetation, trample, dig, and generally stir up their habitat.
In addition to their "bulldozing" activities, Galapagos tortoises may be the gardeners of Galapagos due to their prodigious consumption of fruits and seeds. The tortoises eat fruit whenever it is available, and their relatively benign digestive system means that most seeds pass through the digestive track unscathed and are planted intact in a rich pile of nutritious dung. Data from the Galapagos Tortoise Programme show that a single pile of tortoise dung may contain over 6000 seeds from up to nice species of plants. Research also shows that seeds may remain in the digestive tract of tortoises for over a month, during which time a Galapagos tortoise may move many kilometres. In fact, it is likely that Galapagos tortoises move more seeds from more species over larger distances than any other vertebrate group on Galapagos making them truly "the gardeners of Galapagos".
Galapagos tortoise ecology: The Gardeners of Galapagos
Ultimately, the behaviour of animals is thought to have evolved to maximise reproductive success. So in a migratory system like that of the Galapagos tortoises in which some individuals migrate and others do not, an important question is which strategy is better? Is it better to wait out the dry season, hunkered down and conserving energy, or is it better to migrate into more favourable conditions, or are both equally good? Why do some females migrate all the way to the coast to lay their eggs, and others travel only half way down the slope? These kinds of questions are behind a recently launched pilot study of tortoise nesting and the survival of eggs and hatchlings. Before getting to complex evolutionary strategies, more basic data collection is necessary first. Team members of the programme are now assessing the distribution of reproductive tortoises in nesting areas, seasonality of nesting, incubation temperatures at different nest sites, weight and size of eggs, fate of eggs, and finally the fate and movements of hatchlings using radio-telemetry.
If scientific results are to be useful for conservation, they must be made available to decision makers and the general public in compelling ways. The Galapagos Tortoise Programme works closely with the Galapagos National Park Service and science outputs are available to feed directly into management. Many children on Galapagos rarely visit the national park and despite living in an archipelago that is 97% park, urban living is the norm. Therefore exposure to tortoises and their environment is limited. Therefore the Galapagos Tortoise Programme has initiated an outreach component for school aged young people on Galapagos, in collaboration with the Galapagos National Park, the Ecology Project International and the Houston Zoo. The aim is to inspire the next generation of conservation leaders through a combination of hands on practical activities within the framework of the research programme, coupled with curricula activities in class to back up field experiences. To facilitate deeper understanding of the secret lives of Galapagos tortoises, all of the tortoise tracking data available to the general public via an online repository of animal tracking data called www.movebank.org, from which the data can be downloaded in several forms, including GoogleEarth tracking files.
Outreach and education
Human beings have long been fascinated with the spectacular phenomenon of long distance animal migration. Be it thundering herds of wildebeest a million strong doggedly walking across the Serengeti plains, or little arctic terns flying from pole to pole and back each year, or monarch butterflies dancing their way from Mexico to Canada over three different generations, migration inspires the imagination. Aristotle wondered where the European songbirds went in winter, but recognised that they fattened up before they disappeared. Centuries later in 1835, a young Charles Darwin pondered why Galapagos tortoise trails on San Cristobal Island often continue for kilometres, usually up and down hill and frequently ended at water holes. The locals told him it was because the tortoises migrate over large distances. Though islanders continued to see seasonal differences in tortoise distribution, Darwin's early observations were never confirmed in detail, and the movement patterns of Galapagos tortoises remained obscure. Realising the potential significance of long distance migration in a giant terrestrial reptile for both conservation and science, in 2009 the Max Planck Institute for Ornithology funded a pilot study to fit GPS tags onto ten tortoises on Santa Cruz Island in the heart of the archipelago and document their movements over two years.
Tortoise GPS tag basics
The tags, made by a German company called e-obs Digital Telemetry, combine five basic components: a GPS unit, an Accelerometer (like the one in a smart phone), a memory chip to store data, a radio beacon to enable radio-tracking, and a wireless communications device with which to upload the stored data to a handheld "base station". These are all connected to a battery back and embedded in a block of tough, hopefully tortoise proof, epoxy. The tag is glued onto the carapace (shell of the tortoise) with non-toxic plumber's epoxy. The tags collect and store a GPS fix ((latitude, longitude, date and time data) every hour to provide a detailed picture of tortoise movements around the clock. The accelerometer unit monitors change in orientation of the tag on three axes (up and down, side to side and left to right) during a short pulse (four seconds) every five minutes, which gives a measure of activity.
It is an odd concept to attach a state of the art GPS tracking device onto a giant tortoise who was perhaps alive when Lincoln was President of the USA, and Charles Darwin published "On the Origin of Species by Means of Natural Selection".
Sure enough, giant tortoises migrate up and down the slopes of the extinct volcano that is Santa Cruz. During the dry, cool season, from June to December, the tortoises tend to be found in the uplands of the island where it remains humid year round and therefore plants continue to grow throughout the year. Tortoises seem to like feeding, often for hours on end, on grasses and small herbs. Then as the hot rainy season begins, the tortoises migrate down into the lowlands, often to sea-level; a journey of up to 10kmthat may take three weeks to complete. The tortoises seem to be drawn to the lowlands because the rains produce a rapid bloom of highly nutritious thick vegetation. The tortoises feed for several months, during which time they also mate, until the dry season returns and the vegetation desiccates, and which the males begin returning to the humid highlands, while the females remain in the lowlands to lay eggs. After nesting females also move into the highlands, though intriguingly, some females stay year round in the lowlands. Furthermore, unlike most migratory species, it is only adult Galapagos tortoises that migrate, though the reasons for this are not yet clear.
Tortoise movements on Santa Cruz
Tortoise movement and migration
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