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Post date: Jul 5, 2013 11:54:20 PM
I'll start with the exciting news: we've now deployed all of our transmitters! Having added three extras midway through the season, we ended up with a total of 63, all of which are now collecting data around the Gulf of Mexico. Next week we'll be finished with the field season, and the less-glamorous work of sorting and analyzing data will begin.
While writing the last entry, I realized that I had never really described the process of trapping, measuring, and releasing a pelican. Here's how it works:
Step 1- Set a snare on a nest. When a pelican lands, pull the snare closed around its ankle.
Leg snare made of fishing line and nylon string
Elizabeth pulls a snare, catching the target bird (raising its wings near the orange flag) on Raccoon Island, LA
Removing the trapped bird from its nest usually requires two people: one to hold the bird, and one to remove the snare
Step 2- Put the pelican in a bag (in our case, a pillowcase modified with a drawstring). This helps to keep the bird calm and allows us to weigh it using a spring scale.
Most of the pelicans we catch weigh between 2.5 and 4 kg, or 6-9 lbs
Step 3- Take a sample of blood from a vein in the tarsus (lower leg). These samples will be used to check the health of the bird, test for chemical contaminants, and determine its sex. We also take several feathers to analyze for mercury content.
Step 4- Band the bird. The bands we use are made by the U.S. Geological Survey's Bird Banding Lab and provide a unique 9-digit number that will help identify the bird if it's ever found again, alive or dead.
A string of pelican bands
Banding a pelican
Step 5- Measure the lengths of the tarsus, wing, and culmen (upper part of the bill). These measurements, combined with body mass, will help us compare the physical condition of birds between different regions, giving us an idea of how foraging behavior or contaminant load can affect health.
Measuring the tarsus
Measuring the culmen
Step 6- Attach a transmitter.
Transmitters are held in place by knotted teflon ribbon secured with super glue
Step 7- Collect any fish that the bird has regurgitated. Sometimes, in the stress of capture, a pelican will drop the fish in its pouch or gullet, which lets us see exactly what it has been eating.
A single meal for an adult pelican from Shamrock Island, TX: two Atlantic cutlassfish and a selection of smaller prey
Fish dropped near a pelican nest on Shamrock Island, TX
Step 8- Release the bird.
A tagged pelican flies away on Felicity Island, LA
From capture to release, the process usually takes us 15-20 minutes. Once released, tagged pelicans usually spend time away from the nest preening to restore the waterproofing of their feathers, but typically return to their nests within a few hours.
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