Coyote Creek Field Station Geolocator Study - Linking the Migratory Geography of the Hermit Thrush and Parasite Transmission Sites with the Aid of Geolocator Technology
PHOTO 1: This past winter, SFBBO collaborated with Point Blue Conservation Science (formerly PRBO) and San Francisco State University MS student, Allison Nelson, in an exciting study of the Hermit Thrush, a North American migrant passerine revered for its exquisite song.
Geolocators, tiny devices that help researchers determine the routes and destinations of migratory birds, were applied to 15 Hermit Thrushes wintering at Coyote Creek Field Station.
Point Blue attached 17 geolocators to Hermit Thrushes wintering in the Point Reyes area.
These battery-powered devices record light level data every 5 minutes throughout the year, which can then be translated into latitude and longitude.
After recapturing the birds when they return next winter, researchers will remove the tags, download the data, and estimate the bird's location throughout the year.
PHOTO 2: Hermit Thrushes (Catharus guttatus) that winter in the SF Bay Area may breed in Oregon, Washington, British Columbia, Alaska, or the Yukon territories.
Exact routes and stopover locations of these birds are unknown.
Existing estimations of breeding grounds are based on band recoveries or morphological data collected from museum specimens.
The current study will permit us to more precisely define the migratory geography of the Hermit Thrush.
The map on the left indicates potential breeding destinations of Bay Area wintering Hermit Thrushes. (Note that red lines do not represent actual migration routes.)
PHOTO 3: Geolocators are attached to the bird with a stretchy leg harness.
An aerodynamically designed light stalk lifts the light meter above the feathers, reducing the possibility of interference from shading.
Here, Point Blue researchers Renee Cormier and Diana Humple attach a geolocator to a Hermit Thrush.
PHOTO 4: Geolocators record data but do not actively transmit it.
In order to retrieve the tags and download data, the individual must be recaptured approximately a year later at the same site.
Hermit Thrushes exhibit high site fidelity on wintering and breeding grounds.
This means that they return to the same site each year after a migratory journey that may span over 1000 miles.
The data record shown on the left is that of a bird originally captured at Coyote Creek Field Station in 2006.
It has been recaptured 15 times, in the same three nets, every winter since 2006.
A geolocator was attached to this individual in 2013....we hope it returns again next winter so we can determine where it spent the rest of the year!
PHOTO 5: Geolocators weigh about one gram, approximately the weight of a paperclip, only 4% of a Hermit Thrush's body weight.
PHOTO 6: Birds wearing geolocators are also color banded.
This aids field identification of tagged birds that have returned but that have not yet been captured at the banding stations.
If necessary, staff and volunteers can then "target net" these birds, luring them into mistnets using song playbacks.
PHOTO 7: Throughout the fall and winter, Allison Nelson has been taking blood samples of tagged and non-tagged Hermit Thrushes to use for DNA analysis.
Because male and female Hermit Thrushes are monomorphic, sex could not be determined in the field.
DNA analysis will allow us to determine the sex of the birds.
We can then learn if tagged males and females follow different migratory routes, winter in differing locations, or arrive on wintering and breeding grounds at different times.
Blood samples of birds are usually taken from the brachial vein.
PHOTO 8: In addition to investigating the migratory geography of Hermit Thrushes, Allison is also using DNA analysis to identify vector-borne haemosporidian (blood) parasites that these birds carry.
Parasites such as those of the Plasmodium or Leucocytozoon genera can cause avian malaria or similar diseases.
Parasite data acquired from blood samples of tagged birds will be combined with data from Hermit and Swainson's thrushes sampled at known breeding or wintering locations.
By analyzing these data together, we can estimate potential locations of parasite transmission and determine if certain parasite lineages are unique to Catharus thrushes.
Blood slides have also been prepared for morphological identification of parasites.
All DNA analysis and microscopy will take place in the Avian Parasitology lab of Allison's SFSU advisor, Dr. Ravinder Sehgal.
PHOTO 9: While the current study focuses on Bay Area wintering Hermit Thrushes, Allison also hopes to pursue a geolocator study of locally breeding Hermit Thrushes.
The latter populations are found only at high elevation coastal sites in Santa Cruz or Point Reyes.
Blue markers indicate sites where tags have been attached to wintering birds.
Red markers indicate ideal locations for a geolocator study of breeding Hermit Thrushes.
PHOTO 10: Hermit Thrushes wintering at CCFS are a darker, warmer brown.
PHOTO 11: Hermit Thrushes breeding in the local coastal ranges are a paler gray.
This bird is from a population that Allison Nelson has banded and taken blood samples from in the Santa Cruz mountains.
PHOTO 12: This research can help identify breeding, wintering, and stopover sites vital to our local Hermit Thrush populations.
It can clarify also relationships between populations found in different locations, and will aid disease researchers in the study of avian malaria.
SFBBO, Point Blue Conservation Science, and SFSU look forward to sharing our results after our birds have returned next winter!
Geolocator Study Updates
Oct. 30th, 2013: We captured our first returned tagged Hermit Thrush at SFBBO's Coyote Creek Field Station, a female!
Oct. 17th, 2013: We captured our first returned tagged Hermit Thrush at Pine Gulch!
Nov. 9th, 2013: We captured our second returned tagged Hermit Thrush at the Coyote Creek Field Station!
Dec. 1st, 2013: We captured another tagged Hermit Thrush at Pine Gulch!
Dec. 21st, 2013: We captured two more Hermit Thrushes with geolocators at the Coyote Creek Field Station!
Geolocator Study in the News!
Visit here to see the latest media coverage of this exciting study! Visit SFBBO's Facebook page to see photos of our recent captures!