Prothonotary Warblers

​By Adrienne Frank and Gary Driscole

​In late winter, Gary Driscole prepares for the coming year of monitoring Prothonotary Warbler (PW) boxes in Dragon Run. He repairs or replaces boxes and checks their placement in the river. The warblers typically return to the Dragon in late April to raise their young; the boxes will be ready for their return. 
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The PW is also known as the swamp warbler. It is a bright yellow bird named after an official of the Roman Catholic Church known as a prothonotary (like a cardinal, only dressed in yellow). The warbler breeds in the swamps and rivers of the eastern half of the U.S. but migrates to Central and South America during our winter.
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Gary has 20 boxes on poles in the water along the main channel of Dragon Run between the Big Island property and Mascot bridge. The boxes are specific to the warbler’s needs in size and location. The pole for the nest box is best placed in the water, and the box is mounted at least 4 feet above and facing the water. The bird’s entrance hole is 1¼ inches across, and the box itself is 8 inches deep and 5 ½ inches wide. The size helps to keep out predators and larger animals in search of a home.
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​PWs have several predators including raccoons and snakes. Luckily, Gary has never seen evidence of these predators in the Dragon’s boxes. However, other factors have affected nesting and eggs. Chickadees begin breeding early in the season and often use the boxes. So Gary counts Chickadee fledglings in addition to Prothonotaries. Occasionally, eggs disappear or have holes in them, and this could be the result of woodpeckers. Weather also contributes to poor nesting outcomes. A cold and rainy spring can affect breeding and also the boxes themselves. Boxes and poles can be knocked over by high water or nests can be soaked and ruined. Wasps and bumble bees sometimes make their homes in boxes and interfere with the bird’s nesting.
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​PWs eat insects and when the spring is cold and rainy the insect population decreases. PWs eat water insects (i.e., mayflies) and caterpillars. A study conducted by Virginia Commonwealth University (VCU) found that PW chicks with mayflies present in their diet were healthier than those without.
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​Gary collects data about the nests by recording nest height, number of eggs, and number of fledglings. Typically, the height of the nest, made with moss, is about 4 inches deep. Sometimes birds build right to the top of the box, making it difficult to look inside. Sometimes, if they must lay their eggs quickly, there is very little moss in the bottom. Typically, there are 4 eggs in a brood and most of them fledge. In the last 15 years, the average number of fledglings was over 60. The lowest number of fledglings was 32 when the spring was cold and wet. The highest number was 74 when some birds had 3 broods and ended their season in August, instead of July.
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VCU has been studying PWs since the late 1980s, and they support boxes along the James River, Northwest River, and other locations in south-eastern Virginia. Over the years, Virginia has become a leader in supporting PW breeding. Each year, Gary contributes data to VCU’s continued research.

​Gary began his adventure with PWs in 2007 when Teta Kain asked Gary if he would consider removing or repairing boxes that were left behind by Mike and Lorna Anderberg who monitored the boxes but moved out of the area. In 2008, Gary entered Basic Training for the Master Naturalist program. One of the speakers was Brian Taber, the President of the Virginia Coastal Wildlife Observatory (VCWO), and he talked about VCU’s research. With Brian’s help Gary began monitoring and sending data to VCU and sharing the data with CVWO and FODR.

In 2017, Gary helped Lesley Bullock and her graduate student Jessica Reese conduct additional research of PWs in Dragon Run. Jessica caught and examined a dozen or so warblers to check their health. She measured size, fat layers, collected feathers, and banded them. Months later, her banded birds were found in Columbia in South America.

Survival of these birds is habitat-related. Coastal areas here and in Columbia face habitat loss due to increased clearing for development and other environmental conditions. Sea level rise, which happens first in the low-land swamps, decreases flora and fauna that the PWs use for survival.  
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Gary will conduct weekly monitoring beginning in April and throughout June,  July, and perhaps into August.  At the end of the season, he will send his data to VCU and will report his findings to FODR.