The migration is underway. The birds have begun to leave Maine. For the next two weeks, the trickle will turn into a torrent. Where will everyone go?
Good question. Birds are disappearing from the planet at an alarming rate. In North America alone, almost three billion birds have disappeared in the last 50 years.
Collisions with man-made structures and outdoor cat predation account for much of the decline, but habitat loss is likely the main cause. For migratory species, both their summer and winter habitats must be conserved if we want to stem the trend.
That’s how Emily Filiberti found herself interning at a nature reserve in Jamaica a few years ago. Filiberti is now a graduate student at the University of Maine. She spent this summer in Wisconsin tracking golden-winged warblers, a species that is disappearing even faster than most other birds. That’s where she made an amazing discovery.
Last spring, Filiberti and his team captured some of the golden-winged warblers in the research area and equipped them with Nano Tags. These tiny transmitters are part of the Motus Wildlife Tracking System, a technology less than a decade old that takes advantage of miniaturized electronics. The transmitters are so small that they can be attached to the butterflies.
Suddenly, the receiving station picked up the signal from a different species, a female redstart that had been tagged in Jamaica. In fact, she had been tagged two months earlier by her old supervisor, at the exact same place where Filiberti had studied.
Eight days later, the station picked up the signal again. This bird was not just passing through. It was probably nesting. Using a handheld antenna and immense patience, Filiberti managed to track the redstart back to its nest, and even catch a glimpse of two speckled eggs during a time when the bird was out for a snack.
So, there it was, an individual bird whose exact winter and summer territories were known, 2,000 miles away. The odds against such a discovery are incalculable.
First, redstarts have one of the widest breeding ranges of any warbler in North America, stretching west across the continent from Newfoundland to British Columbia, and south almost to the Gulf Coast. That’s a lot of real estate. Second, migration is dangerous. Many birds do not survive the journey at all. Third, how often can the same researcher study both sites at each end of the migration?
Maybe that’s the future. Traditional bird banding is still valuable, but technological advances make it possible to track some birds via satellite, using GPS transmitters. Motus technology is a game changer. With enough receiving stations set up along migration routes, the exact route taken by tagged birds becomes clearer.
Amber Roth is Filiberti’s advisor at the university. Amber is using Motus technology to study some of Maine’s most vulnerable species.
Grassland birds are in steep decline. When bobolinks leave the fields of Maine, they migrate to the grasslands of Argentina. The signal from a tagged bobolink was picked up at 13 different stations during its journey south. The bird disappeared when it crossed the Caribbean, but the signal sounded again when it made landfall in Colombia.
This type of monitoring increases the ability of scientists to follow bird populations. Each field guide displays distribution maps for each species, showing the full extent of where the birds breed, migrate and winter.
What the books don’t show is different geographic populations migrating to different places. For example, East Coast birds may winter in the Caribbean islands, while West Coast birds head to Central America. Knowing such details improves our chances of conserving particularly important bird areas.
We can also track the migration patterns of males, females, and chicks to see if there are any significant differences. Such differences are particularly notable in certain species.
For example, adult male sandpipers often leave their breeding grounds before females, who then leave before the young.
As you would expect with such a small transmitter, the signal is not strong. A tagged bird must be within 15 kilometers of the receiving station to be picked up, and much closer if hills and trees get in the way. At short ranges, biologists can use a handheld antenna to locate a stationary bird, as Filiberti did.
How exciting it will be if this little redstart returns to Jamaica and calls the station upon arrival! We are cheering it on.