Geolocators 2.0 - Looking to Further Our Understanding of Prothontoary Warbler Migration

In April 2015, we recovered a single geolocator from a Prothonotary Warbler (aptly named “Longshot”). This small device gave us amazing insight into the migration of the "swamp canary" (read about it here). 

Longshot, pictured here during his recapture in April 2015, wearing the geolocator that he had carried since the previous July.

But in order to learn even more about the migration of this imperiled bird, we deployed eight more geolocators on Prothonotary Warblers earlier this spring. Below, we'll describe the process for attaching these miniature tracking devices to these birds. On our next post, you’ll get to meet the eight special birds that we need your help finding next spring.

We received our shipment of 8 geolocators in May 2016. Each of these tiny devices weighs 0.45 grams, which is about 4% of the body weight of the average Prothonotary Warbler. The general rule for attaching a tracking device to a bird is to stay below 5% of their body weight (in order to not risk negatively affecting it).  Tracking technology miniaturized enough to attach to a bird this small has only been around for the last few years!
  

Eight light-level geolocators arrive at Beidler Forest in May 2016. Learn how these devices work here.

In order to attach a geolocator to a bird, harnesses are made using Stretch Magic (a common type of jewelry cord). Harnesses are tied in a knot creating two loops, and then precisely measured in order to fit around the legs of a Prothonotary Warbler. Once each harness is accurately measured, they are superglued to the geolocator. 

After the knot is tied, each loop must be accurately measured to a specific length. If the length of the loop is just one centimeter off, the harness might not fit the bird correctly.

Once the harness has been measured, the knot is superglued to the geolocator. Pictured here is Aaron Given, Assistant Wildlife Biologist for the Town of Kiawah Island. Aaron helped us get permitted for this project, make harnesses, and deploy each unit. We couldn't have done this project without his help - thanks Aaron!

Once the glue dries, we trim off the excess cord and the geolocator is officially ready to go!

Once the harnesses are made, we hook the geolocators up to computer software, double-check that they are recording light levels, and then the geolocator is ready to go!

A geolocator with harness attached to leads, allowing us to communicate with the individual unit. We use this to calibrate each geolocator, double-check that they are functioning correctly, and most importantly...download the data when we (hopefully) recover them next year!

Now that are units are ready to be put out, we strategically choose the best candidate Prothonotary Warblers out of those that we've color-banded in the past. This is one of the most important reasons we color-band: since we can use the bands to identify each bird uniquely, we can monitor their return rates and breeding success. From this data, we can determine which of our birds have 1) migrated in past years and returned to Beidler and 2) successfully bred this year. These two factors often influence an individual's likeliness to return in subsequent years, and thus are good metrics for determining which birds to use in this project. 

With that in mind, the photo below is a quick overview of the band colors that we've used over the last three years. That way you can learn the colors of each bird carrying a geolocator and you'll be ready to help us find them next spring!

Each bird gets an aluminum band (marked as "A" on right) with a number on it, as well as a unique combination of three colors. Since the bands weigh next to nothing, there is no worry of them hurting or adversely affecting the birds. Using the numbers below each color, we assign an alphanumeric code to each bird.

Contrary to what you  might think, the harness and geolocator do not go over the birds' wings (although sometimes we call it a backpack); instead, they go over the legs and each loop rests up near the bird's hip. 

Putting on the first geolocator.

First gelocator attached! The unit is designed so that the light stock (the lower, white end) points up from the bird, thus allowing it to record light level readings without accidentally being hidden beneath feathers or obstructing the bird's flight.

In our next blog post, we'll introduce to you the eight Prothonotary Warblers that received geolocators in 2016 so that you can join us in looking for them next year when they hopefully return to Beidler Forest!