Spotlight on Zoo Science - August 6, 2004
Mapping the Habitat of a Jewel
National Zoo scientists map habitat to rediscover a treasure in Myanmar's lowland forest.
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A male Gurney's pitta on the forest floor. Image by P. D. Round/ BirdLife. |
Gurney’s pitta (Pitta gurneyi) is the rather dull name of a brilliantly colored bird also known more poetically as the “jewel thrush.” Its history is a tale of a treasure found, then lost, and found again, and again. First described from southern Myanmar (Burma) in 1875, it appeared frequently in collections from southern Myanmar and adjacent areas in peninsular Thailand. But after scientists had not seen it for 50 years—from 1936 until 1986—it was on the verge of being declared extinct.
In 1986, however, a tiny population, numbering at least three dozen or so pairs, was discovered in a lowland, semi-evergreen rainforest region of Thailand. This habitat, known as “Sundaic forest,” was, and continues to be, rapidly lost and fragmented, thanks largely to clearing for rubber and oil palm plantations. By 2003, perhaps only 20 or 30 of the birds remained in Thailand, and, because the last confirmed sighting in Myanmar was in 1914, scientists believed that it had been extirpated there.
In 2003, though, a team of Burmese and British ornithologists, working with 
BirdLife International and led by Jonathan Eames and U Htin Hla, rediscovered Gurney’s pittas during a month-long survey of Sundaic forest in an area of Myanmar called the Tanintharyi Division or the Tenasserim. They found the birds at four different sites, at one of which were ten to 12 pairs.
But the onset of the rainy season and the lack of accurate maps on the distribution of remaining lowland forests handicapped the survey and made a full-scale assessment of the remaining population impossible. Having made this incredible find, the team knew that more extensive studies were needed to determine the status of the species and its habitat in Myanmar.
At about the same time, National Zoo scientist Peter Leimgruber and his graduate students had finished a countrywide forest-cover assessment of Myanmar, based on comparisons of Landsat satellite imagery from the 1990s and 2000s. Leimgruber and his students had spent three years analyzing more than 86 satellite images to determine the condition of Myanmar’s remaining forests.
Their analyses revealed that Myanmar, a recognized biodiversity hotspot in Southeast Asia, has more remaining forest cover than all of other countries in mainland Southeast Asia combined. These forests may be the last strongholds of many of the larger endangered mammal species of Asia, including tigers and Asian elephants, and—potentially—for the newly re-discovered pitta.
So, BirdLife International joined forces with the National Zoo’s Conservation GIS Lab to map remaining Gurney’s pitta habitat and to repeat a survey the following year.
Gurney’s pitta has very exacting habitat requirements. These birds need flat, lowland forest, that is, forest below 160 meters (525 feet) in elevation on slopes that are less than ten degrees. Here, the secretive birds, which live mostly on the ground, feed on earthworms, insects, and snails that they find on the forest floor. They build nests just a meter or two (3 to 8 feet) above the ground, usually in thorny trees, but young appear to heavily preyed upon, by snakes for instance. Three or four eggs are laid at a time, but one study in Thailand found that, on average, only one chick per nest survives.
Using data from BirdLife International’s first survey, Leimgruber and masters’ student Dan Kelly developed a GIS model to identify Myanmar’s remaining lowland forests and the associated Gurney’s pitta habitat. For the analysis, the National Zoo team combined their Landsat satellite data with data on global elevation that was developed during NASA’s Shuttle Radar Topographic Mission. Only satellite maps of forest habitats below 160 meters in elevation and on slopes less than ten degrees were included.
The team found large areas of lowland forests, covering 4,705 square kilometers (1,817 square miles) at the southern tip of the Tanintharyi Division. Of these, 3,496 square kilometers (1,350 square miles) were in areas with slopes less than ten degrees. Based on previously reported population densities, these habitats potentially could support between 5,152 and 8,586 pairs of Gurney’s pittas.
However, much of this habitat is threatened by habitat degradation, mainly from the development of oil palm plantations. In some areas the rate of forest loss was as high as 30 percent in ten years. Many of the remaining habitat areas were in small and fragmented patches of less than one square kilometer (less than half a square mile) in size. The five largest patches had a total area of 1,431 square kilometers (552 square miles) and these ranged in size from 137 to 467 square kilometers (53 to 180 square miles). (See map below.)
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In early 2004, BirdLife’s team returned to the region with the new maps. They found more than 100 pairs of the birds, increasing the known population by more than tenfold. Much of the habitat Leimgruber and Kelly mapped is already in the process of conversion into oil palm, but two of the largest patches are virtually untouched.
One area is adjacent to a proposed national park, and BirdLife has petitioned the Myanmar government to establish the park quickly and to include within its bounds the habitat of newly found Gurney’s pitta populations.
Gurney’s pitta remains listed as Critically Endangered on the World Conservation Union (IUCN) Red List of Threatened Species, and only urgent and sustained conservation efforts will keep this species from going extinct. But the future of this jewel looks much brighter than it did just a few years ago.
Gurney’s pitta is one of about 30 species of passerine birds in the family Pittadae; two species are found in Africa, the remainder live in tropical Asia and Australasia. Pittas are stocky birds, about eight-inches long, with short tails. In most species, males boast dazzling colors and even the more drab females are strikingly marked. Thirteen of the species are on the Red List, and little is known about most of them.
—Peter Leimgruber
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