“Warbler!” The call was excited, but not so loud as to scare away the bird. I turned my attention briefly toward my friend’s voice and then pivoted to see what he was looking at.

A small yellow bird was flitting about at the base of some nearby scrub, illuminated by springtime sunshine. I pulled up my binoculars for a closer look. The undersides were yellow, but it was mostly brown on its wings and back. A warm chestnut cap stood out above a bold yellow eyebrow. As it continued to look for insects, its tail was in constant motion.

The palm warbler (Setophaga palmarum) was just passing through the Chesapeake region, on its way to breeding grounds in Canada.

My friend and I were part of a small group searching for early migratory birds. From the moment we got out of our cars, the full rush of spring was upon us. Fields of brown were greening up, the forest was leafing out and bird song filled the air. The smell of soil coming to life was a perfect complement to the abundant sunshine.

We walked along Goose Pond Trail, a short walk that divided a wooded area from an open meadow in the Patuxent National Wildlife Refuge near Laurel, MD. It was perfect for birding, allowing us to hear and see birds in distinct habitats by simply turning left or right.

Other birders had reported successful trips to the refuge in recent days, and we were confirming their sightings with every step.

Tens of thousands of birders now use the eBird app designed by the Cornell Ornithology Lab. Checklists are submitted year-round, giving scientists large datasets to analyze and post online. Later that day, I tallied the species I saw at the refuge. It took just a few minutes to enter the day’s sightings.

The U.S. Geological Survey, along with its sister agency in Canada, conducts an annual Breeding Bird Survey. Add in the legendary Audubon Christmas Bird Count and now the eBird data, and scientists have a wealth of information on birds and their locations throughout the year. Using these data, professionals are able to determine the range and migration patterns of hundreds of avian species in North America with newfound accuracy.

These robust citizen-scientist efforts, combined with user-friendly tools, enable birders to know when and where they are likely to see various species. You can even find hotspots like Patuxent in April. The location was especially apt. The USGS scientists studying birds are located at the Patuxent Refuge, a unique partnership with the Fish and Wildlife Service, which oversees the nation’s wildlife refuges.

The palm warbler I saw was easy to spot even though it was partially obscured by the rapidly greening scrub. The bird advertises its presence by its constant tail-wagging. As it does so, it shows off its yellow undertail.

During migration, palm warblers can be found in every state from the Mississippi Flyway to the Atlantic Flyway. Here in the Chesapeake, we typically see the “eastern” population in April. These birds are distinguished from the larger “western” population by their russet-streaked yellow undersides. The more numerous group has the same streaks but is mostly white underneath. Both subpopulations can be seen in the Chesapeake region during the fall migration, which typically extends from late September through early November.

Palm warblers build their nests by hollowing out a small cup in sphagnum moss at the base of a conifer tree in the bogs and boreal forests that stretch from Maine to Alberta. As the female sits on the nest, her yellow or white underside is hidden, revealing only browns and rusty reds on top. The camouflage works, keeping the female and her eggs safe from predators. With a clutch of four to five eggs, palm warblers are able to maintain a stable population.

During the winter, palm warblers head to the Atlantic Coast, from the Carolinas down through Florida, the Gulf Coast, the Caribbean and into Central America.

As we witnessed on our field trip, palm warblers eat insects. They usually feed on the ground, foraging for their dietary staple. During the winter, especially during cold snaps when bugs are less active, palm warblers will also eat berries and fruit. Regardless of the season, the distinctive tail-wagging is always present.

I love birding’s rewarding mix of art and science. The beauty of warblers like the palm captures my imagination. Looking at a bird and knowing that it is on its way to Canada provides depth to the heart-jumping immediacy of catching a glimpse of a wagging tail.

On this lovely day, the palm warbler rewarded me anew as it lifted my heart and sparked my mind. It was a mighty feat for a tiny bird, helped along by a hidden flock of birders pecking out data onto the worldwide web.