Tracking Hummingbirds

By Mark Roberti

Researchers are using RFID to learn how deforestation affects pollination.

  • TAGS

Ecologists are increasingly concerned that deforestation and development are disrupting the habitats and movements of the birds and insects we depend on to pollinate plants for our food supply. But studying pollination isn't easy. It's hard to track insects, which are small and often don't live long.

It's also hard to track hummingbirds, which play an important role in pollinating a variety of tropical and temperate plant species. But Adam Hadley, a postdoctoral researcher in the Department of Forest Ecosystems and Society at Oregon State University, and his team are doing just that, thanks to radio frequency identification. "Habitat loss affects many pollinators, including birds," Hadley says. "With hummingbirds, we get a better idea of how deforestation affects their movements."

The antennas are placed like "halos" over flowers so they are perpendicular to the transponders when the birds visit.

Hadley and his team initially employed small radio transmitters, similar to those used to track migrating deer, elk and other large animals. They shaved a few feathers off the tiny birds and glued a transmitter to each bird's back. But this required the team to follow the birds with radio receivers. Moreover, the transmitters often fell off the birds' backs, and the batteries died after roughly two weeks.

A member of the team had heard about RFID transponders that could be implanted in animals. The team purchased glass-encapsulated 134 kHz transponders just 8 millimeters long and weighing only 0.033 grams, from West Fork Environmental, an Olympia, Wash., company that offers research products and services.

The transponders have a read range of just 10 centimeters, which makes it impossible to track the birds in real time. Hummingbirds vary in length from 8 centimeters to 15 centimeters, depending on the species, so the researchers had to observe them at an aviary to determine the best placement of antennas to capture data consistently without affecting how the birds hover around flowers. They learned they had to place the antennas like "halos" over flowers so the antennas would be perpendicular to the transponders when the birds visited. Small birds must be able to hover within the antennas while feeding; otherwise, transponders on long-billed species will be too far away to be read.

One big advantage of RFID over radio telemetry systems is that readers can be placed permanently in flower patches frequented by hummingbirds, so the birds can be tracked as they return to the same feeding spots year after year. In addition, with RFID, the birds only need to be captured once to implant the tags, rather than repeatedly to affix new devices to their backs.

So far, roughly 300 birds have been implanted with the tiny RFID transponders, which has enabled the researchers to collect a wealth of data in Costa Rica, where the study is taking place. "We are still analyzing all the data," Hadley says. But it's clear that it will provide some meaningful insights into the feeding habits of the hummingbirds and the impact that deforestation has on those habits."

Antenna photo: Evan Jackson | Hummingbird photo: iStockphoto