Each week on the blog we pull back the curtain on our Wildlife Ecology & Conservation graduate students’ seminar class. This post is by master’s student Elysia Webb.
Dr. Lisa Davenport had a mystery on her hands: her birds kept disappearing.
During most of the year, the Orinoco geese and black skimmers happily nested and fed on the banks of the Amazonian rivers in Parque Nacional de Manu, Peru. But when the drenching rains of the wet season fell in November, they vanished. When the rains subsided in April and the rivers shrank, they reappeared just as suddenly. Especially mystifying was that the Orinoco goose, “the only true forest goose,” was classified as non-migratory. To figure out where the birds went, Dr. Davenport decided to track them.
Bird tracking techniques, which were developed to measure how avian diseases could affect humans, revealed bird “flyways,” or travel paths. While the flyways of Asia and North America are well-mapped, bird migration within the Amazon is poorly understood and researched. Though bird banding research is helpful in studying bird movement in the United States, it doesn’t work as well in the Amazon because the birds there are rarely recaptured by scientists, and bird bands are rarely returned by hunters who catch banded birds.
Understanding patterns of bird movement across the landscape is a pressing issue because of the threats facing the Amazon: Proposed mega-dams will alter the flow of water, petroleum leases will cause deforestation and pollution, and the channelization of waterways will change how water is distributed. For the wildlife that depend on the forest and its water, these changes will have significant impacts. Many fish and birds are important food resources for the people of the region, and they will be impacted as well if migration patterns shift.
Though the Amazon rainforest doesn’t have four seasons, there are important seasonal differences in water availability. North of the equator, the peak flow of water occurs in June and July. South of the equator, peak flow is in January and February. Because of these water differences, the rainforest is a diverse mosaic of habitats. The differences in water also appear to be the driving cause of migration for the black skimmer and Orinoco goose in Manu National Park.
Until recently, the question of “where do the birds go?” was impossible to answer. Now, with advances in technology, wildlife tracking is much easier than it once was. Telemetry units have become smaller and more efficient, so birds are no longer too small to be tracked (some units are so lightweight that they can be applied to dragonflies and beetles). Battery life used to severely limit data collection on long-distance migration, but recent advancements in solar-powered transmitters makes years-long tracking possible.
Using these improved technologies, Dr. Davenport was able to capture geese and skimmers at her field site and outfit them with lightweight transmitters. The transmitters communicate with orbiting satellites, and send regular progress reports back to the researcher. “It’s like the birds are sending letters home,” says Dr. Davenport. The emailed data is highly accessible, and can even be checked from a cell phone.
The “letters home” from the Orinoco geese showed some surprising patterns. This supposed non-migratory bird was clearly migratory, with many individuals flying from Peru to Bolivia during Peru’s wet season. The transmitters showed that the geese migrate at night, possibly to avoid predators such as hawks and eagles, or to take advantage of cool, nighttime air. Two of the birds tagged were a breeding pair and the data showed that they made the journey to Bolivia together, suggesting that mates may stick together longer than the breeding season. The skimmers, on the other hand, showed a much greater contrast. Some skimmers took the same paths as the Orinoco geese, and even ended up in the same park in Bolivia. Others flew over the Andes Mountains in the highest passes to access the Pacific coast. That the skimmers could fly so high was astonishing, and such a migration was thought nearly impossible.
Dr. Davenport’s research is ongoing, but the data is already changing the way we view bird migration in the tropics. Some sites, such as the park in Bolivia, might be disproportionately important to migratory birds. If these crucial stopovers are disturbed, it could be fatal to thousands of birds. Conservation funding should prioritize such sites.
Some patterns of avian migration might even apply to the neo-tropical area of southern Florida, where birds might move to take advantage of seasonal resources. As the human population of the tropics and neo-tropics continues to grow rapidly, migratory birds will suffer the consequences. Understanding their flyways and stopovers will help mitigate human-wildlife conflicts of interest, and preserve these species for generations to come.