Image: J. GILARDI, ¿ 1992
Two football-shaped bunches of feathers nap peacefully on a branch inside a low, gray building at the Bronx Zoo in New York City. These St. Vincent Amazon parrots, miles from their natural habitat and oblivious to the plight of their relatives on an island in the Caribbean Sea, live a protected life at the World of Birds exhibit. But private collectors prize such animals¿each might command over $10,000¿helping to create a demand that often outstrips the supply of legally available birds and fuels illegal trafficking. This demand, on top of natural hazards and the St. Vincent Amazon parrot's small range, has put the species at risk for extinction.
Now, in one example of the growing field of conservation genetics, scientists are compiling information that will aid these birds in a variety of ways. Conservation genetics is an umbrella term for a variety of sciences, including ecology, molecular biology and population genetics. It involves the use of detailed genetic information to better manage a species' population and, in many cases, to try to coax it back from the brink of extinction.
Parrots have more endangered species than any other bird family. The St. Vincent Amazon parrot, found only on St. Vincent Island, was first listed as endangered in 1970. The World Conservation Union (IUCN) specified habitat loss, hunting, hurricanes and trade as causes for their decline. "Historic information suggests they were all the way down to sea level on the entire island. But currently they are in a very small chunk of forest left way up in the mountains," says James Gilardi, director of the World Parrot Trust, a charity that works for the survival and welfare of parrots. "So they're sitting on this little remnant of habitat and they've been chased out of the rest of their range and, consequently, they're exposed to more sorts of perturbations in a more severe way."
The parrots' numbers in the wild hit a low point in the mid-1980s, Gilardi says, after they suffered through back-to-back natural disasters: a volcanic eruption followed by a hurricane. The most recent census found higher numbers of wild birds, approximately 800, and IUCN has since reclassified the parrots as merely "vulnerable." Still, that places them at a "high risk of extinction in the wild in the medium-term future." Birds in captivity are spared the hazards facing their wild counterparts. Scientists are trying to increase this captive population, though not for reintroduction purposes. Instead, they want to ensure a healthy, diverse population of captive birds as a reinforcement to those in the wild.
George Amato of the Wildlife Conservation Society and a graduate student, Michael Russello, initially started working with the St. Vincent Amazon parrots when a consortium of parrot enthusiasts on the island approached them with a seemingly simple question: Is there an uncomplicated way to tell which birds are male and which are female? Because St. Vincent Amazon parrots are what are known as sexually monomorphic, it is impossible to tell males from females just by looking at them. Understandably, this led to difficulties in breeding attempts. Many methods of sex determination are invasive, costly and possibly dangerous to the birds, so "[breeders] used to just watch the birds and then remove pairs they thought would be a good match," Russello explains. "In one case, they removed two males and waited for them to breed."
Amato and Russello applied a straightforward polymerase chain reaction (PCR) test to determine the sex of all the captive St. Vincent Amazon parrots living in St. Vincent and Barbados, a total of 79 birds. The simple test required only a feather tip for analysis. It also provided detailed genetic information about the birds that had never been available. According to Amato, the subsequent step in the process was to try to determine how, exactly, the individuals in the captive population were related to one another. With such information now in hand, Amato and Russello hope that it can be used to implement management strategies to ensure a genetically diverse population that is better able to withstand threats to its survival.