This article is copyright Winston-Salem Journal and appeared in the 8/7/15 Bird’s-Eye View column by Phil Dickinson. It is reproduced here with permission of the Journal.
Wood Thrush declining; groups try GPS tracking
By Phil Dickinson
On a sunny spring morning, an ethereal, flute-like song echoes from somewhere deep in the woods. I pause to listen. Sure enough, every few seconds an “ee-oh-lay” bursts forth. Every bird-lover I know revels in the tune of the Wood Thrush, even though the singer may remain hidden among the leaves.
How long will we hear this song? Due largely to loss of woodland habitat, numbers of this speckle-breasted cousin of the robin have declined by roughly 55 percent in the past 50 years. Future climate changes could imperil this species even further.
Fragmentation of our forests has occurred both where the bird breeds in the eastern United States and where it winters in Central America. Conservation efforts on behalf of the Wood Thrush must take a hemispheric approach, including stops along its migratory flyway.
The problem is that we know very little about the specifics of the thrush’s seasonal movements. Forsyth Audubon teamed up with National Audubon Society’s International Alliances Program and the Smithsonian Institution’s Migratory Bird Center to see if we could discover where some local birds traveled. The idea was to catch birds and attach GPS locator tags to them to monitor their movements.
In Spring 2014, Audubon volunteers scouted local woodlands for Wood Thrushes. Bethabara and Pilot Mountain State Park’s Yadkin River section seemed to have the largest populations and became the focus of our tagging efforts.
Peter Keller, a Smithsonian field biologist, arrived in May to begin trapping. Numerous volunteers were awake and out the door before dawn to assist in carrying equipment, setting up nets and recording data.
Females and young males were banded, but only adult males received backpacks carrying the GPS tags. They were big enough to carry them without hindrance and thought most likely to return to the same nesting areas.
About 50 birds were banded. Of these, 22 received backpacks – 17 at Pilot Mountain and 5 at Bethabara. The tags would record movements during the next 12 months, logging 50 GPS points during migration and the winter season. The data would be precise – within a few meters. We would know exactly where the birds stopped.
One problem – the tags record data but do not transmit. These birds are too small to carry signal transmitters used to track hawks. We would have to recapture tagged birds to retrieve the data! We needed them to return to the same area this past spring.
This May, we returned to Pilot Mountain and Bethabara with another Smithsonian biologist, Tim Guida. How many GPS tags could we recover? Much can happen to a bird in a year and, even if it returns to the same location, we might not catch it. Smithsonian hoped for about 20 percent.
Similar trapping efforts in Indiana, Minnesota and Delaware achieved recovery rates of 20-30 percent. However, we recovered only two GPS tags (9 percent) and netted only four other birds banded in 2014. A tagging effort in New York also had a low result (13 percent). Interestingly, we captured 44 unbanded birds.
Habitat changes due to a prescribed burn at Pilot Mountain may have affected our recovery rate by causing tagged birds to move elsewhere. Bethabara’s relatively small size could have a similar impact. There probably is no single reason.
Results from one tag thrilled local Audubon members. This Pilot Mountain thrush wintered in Belize, where five local members had traveled to work in partnership with Belize Audubon (Bird’s-Eye View, February 7, 2014). The other GPS tag was damaged, and attempts to recover that data continue. It could be valuable to know if that bird also has ties to Belize.
Calandra Stanley works for the Smithsonian Migratory Bird Center. She reports that Indiana results showed a high degree of migratory connectivity. Birds captured there all wintered in southern Mexico. On the other hand, Minnesota and Delaware birds spread to different countries.
Nevertheless, the Belize connection provides inspiration for the two Audubon chapters to continue collaborating in some fashion to protect our birds. Over the next few months, the chapters and the International Alliances Program can figure out what form that cooperation might take.
To hear the Wood Thrush’s song, see Wood Thrush at All About Birds.
Audubon magazine tells the entire story in wonderful detail in the September-October 2015 issue. Wood Thrushes Connect Bird Lovers Across Borders
Ron Morris’ column published in the Journal on April 17, 2104 is also about the Wood Thrush. Wood thrush one of the most gifted singers
Kim Brand’s post on the NC Audubon blog on July 28, 2014 shares more information about Forsyth Audubon’s efforts to help the Wood Thrush. Studying Migrating Wood Thrush in North Carolina