The study of bird migration is being transformed by new technologies. Satellite transmitters and geolocators are now smaller and less intrusive. These tools are tracking birds from breeding to wintering grounds, revealing extraordinary insights into the diversity of migration patterns.
Combined with the torrent of information being gathered and entered into online databases by volunteer birdwatchers, the knowledge gained should drive more effective conservation on the ground and ward off extinctions.
The strength of the latest technologies was highlighted in presentation after presentation at the fifth North American Ornithological Conference (NAOC), a gathering of 1,500 international bird scientists, held this month at UBC. Ornithologists spend hours in the field tracking bird behaviour, food requirements, mating strategies, and migration journeys, all aimed at solving the riddle of why birds do what they do. Their findings help answer the question: what causes population declines?
One reason birds are studied is because they are excellent ecological indicators: widely distributed, rapid responders to habitat and climate changes, and often more easily observed than other animals. It is known that over half the neotropical birds (those that migrate between North America and the tropics) have suffered population declines in the last few decades.
Yet it is still a mystery where many spend their time after the northern breeding season. Peter Marra of the Smithsonian Institute in Washington, D.C., was one of several presenters to emphasize the need for more research into the full lifecycles of migratory birds, as an essential tool for making environmentally sound decisions about global land use and resource exploitation.
There has been an evolution in migration technology. The simplest surveys use only a pair of binoculars, like the Breeding Bird Survey (BBS), on the go in North America since 1966, and Project Feeder Watch since 1987. Both programs involve thousands of volunteer, “citizen science” participants, watching and counting birds, and have contributed enormous amounts of data, much of which is now online.
Bird banding is more complex, but has been in use for more than 100 years. Volunteers join professionals working long hours during migration season to catch birds in mist nets, fit leg bands, and collect biophysical data. Yet birds disperse widely, and of the 64 million birds that have been fitted with little metal leg rings in North America, only 4.4 million bands have been returned and only a tiny proportion of birds recovered alive.
Inevitably, there are questions that cannot be answered by field observation or bird banding, and require other technologies. NAOC presentations showed that scientists commonly use weather radar, radio and satellite telemetry, and light-level geolocators.
Weather radar allows observation of migratory birds at night and can answer questions about large-scale bird movements. Andrew Laughlin, a graduate student at Tulane University, was able to decipher the seasonal movements of tree swallows by locating huge roosting flocks in winter among the cane fields of Louisiana. They showed up as 20-kilometre-wide, doughnut-shaped echoes on the radar screen.
Jill Deppe of Eastern Illinois University used tracking towers to pick up signals of Swainson’s thrush and other migrant songbirds fitted with automated radio-telemetry systems (ARTs), as they crossed the 1,000-kilometre-wide Gulf of Mexico, a formidable feat for any bird. Typically, ARTS have a tiny transmitter and aerial, fitted to the bird’s back or tail. For larger birds, such as raptors, cranes, geese and some shorebirds, heavier satellite systems can be used, that track over even longer distances.
Exciting discoveries have been made, especially of shorebirds, such as the non-stop, 11,500-kilometre flight of a bar-tailed godwit from Alaska to New Zealand, and the repeated journeys between Virginia and the Mackenzie River delta of a whimbrel named Hope. The bird must be caught to be fitted with a transmitter (tricky with a large bird like a sandhill crane) and care must be taken that the instrumentation does not cause the bird distress or bias the research by impeding its behaviour in any way. Birds are not recaptured and sometimes continue sending data long after the expected end date.
While still expensive, transmitters are much lighter than previously; ARTS can weigh less than a gram, and a typical satellite transmitter is about three grams, compared with prototypes of 170 gram two decades ago.
The light-level geolocator, a tiny device pioneered by the British Antarctic Survey, weighs less than 1.5 grams, and determines a migrating bird’s position by the level of natural light. They are smaller and cheaper than satellites, and very long-lasting, though they require recapture of the bird to obtain the data. Much hope, however, is being put in the geolocators ability to answer the many questions remaining about life cycles and migration destinations, at a cost affordable throughout the Americas.
The conservation of birds, and by association many more species which share their habitats, depends upon strong scientific knowledge of their life cycles. With such mobile creatures, some with declining populations, there is a clear need for studies that do not intrude on the bird’s behavior or health. As demonstrated at NAOC, the emerging technologies used by the new generation of scientists appear to be headed in the right direction.
Anne Murray is an independent writer and naturalist and the author of two books on the natural history of Boundary Bay: A Nature Guide to Boundary Bay and Tracing Our Past ~ A Heritage Guide to Boundary Bay, both available at bookstores or online from www.natureguidesbc.com.