Oregon Vesper Sparrows are a declining and at-risk subspecies unique to the Pacific Northwest. This June, spent time in the field placing miniature GPS tags on Oregon Vesper Sparrows to discover their migratory routes and wintering grounds. We thought you might be interested in the process!
First, the GPS tags must be programmed. They have room to store up to 80 GPS locations – but we have to choose how often they take a “fix”. We select the frequency of these fixes so that we can record locations along fall migration routes, during the overwintering season, and (if we get lucky with the battery life) along spring migration routes.
Next we make little harnesses so the birds can comfortably wear the GPS tags like a backpack. The loops you see on either side of the GPS device go around each of their legs.
This work involves hauling around a lot of gear! In the field we need a scope to sight the birds, poles to set up mist nets, and all of the supplies needed to band and tag the birds.
When we arrive at our field site near Howard Prairie, we search for singing males, and try to get a good look at their legs to see if they have colored bands. If their legs are banded, that tells us they have been previously captured. We prefer to put the GPS tags on unbanded birds to increase the percentage of the population we are actively tracking. We specifically targeted males because they are easier to find, and easier to capture.
Next, we set up a mist net near a good perch where the male might fly, and place a speaker playing a Vesper Sparrow song under it. The song is likely to be perceived as a rival male in his territory, and there’s a good chance he will fly into the net while trying to chase away the “intruder.”
Once captured, we extract the bird and put him in a cotton, breathable sack. This helps him remain calm while we get our gear ready.
We bring the sparrow back to a mobile work station. Our first task is to attach a unique combination of colored bands to his legs. The bands let us identify each individual later with binoculars, without having to recapture them.
Next, we fit the sparrow with a tiny GPS tag. We weigh each bird and measure the harness sizes, so that we can use the best fitting harness for the size of each individual bird. The harness loops go around each leg so that the tag sits like a backpack, with the antenna sticking out away from the body and towards the tail.
Finally we release the male Vesper Sparrow and watch to make sure the tag isn’t impeding his normal behavior, such as perching, flying, and singing.
All that’s left is to hope he comes back next year! Because the battery weight needs to be light for a bird of this size, the tag is too small to transmit data; instead the data are stored on the device. This means each bird must be recaptured next year to retrieve the recorded GPS locations.
It’s suspected that Oregon Vesper Sparrows from the Rogue Basin winter in the Central Valley of California, but no one knows for sure. This is the first time this subspecies has been tracked throughout their annual cycle. The precise location information we will gain is critically important. This tagging project builds on nearly a decade of KBO’s work contributing to Oregon Vesper Sparrow range-wide research projects, in partnership with American Bird Conservancy and Center for Natural Lands Management, to better understand this subspecies’s population size and trends, as well as whether their populations are limited by factors related to the summer breeding grounds, overwintering grounds, or survival during migration. With a better understanding of where in the annual life cycle birds are experiencing threats, and how specific summer and winter geographies are linked, we can better identify conservation actions to halt and reverse the declining trend for Oregon Vesper Sparrow.
As this year’s nesting season draws to a close, we wish the sparrows good luck on their upcoming journey south. We hope to see many of them back at our meadow next summer!
KBO’s 2020 field efforts are supported by the Carpenter Foundation, Oregon Wildlife Foundation, and Oregon Zoo’s Future for Wildlife Fund.
Written by Nate Trimble and Sarah Rockwell