December 22, 2015
Thank to Lauren Flesher for this guest student blog post. Lauren describes how Ruby-throated Hummingbirds are expanding their winter range into the southeastern United States.
Hummingbirds, with their small size, striking colors, brilliant iridescence, and rapid hovering flight, are often thought of as flying jewels. Ruby-throated Hummingbirds, found throughout eastern North America, are especially beloved by backyard birdwatchers. But by winter, most hummingbirds will have left their nectar feeders behind, having migrated south to Central America and Mexico. In fact, Ruby-throated Hummingbirds are known for their amazing migration across the Gulf of Mexico, a 500-mile journey that takes 20 hours of non-stop flying. That’s quite a feat for a bird that only weighs a few grams! But over the last 25 years, some hummingbirds have found a way to avoid that strenuous flight by wintering in the warmer parts of the southeastern United States. The wintering range of the Ruby-throated Hummingbird has expanded dramatically in the last several decades with the range shifting nearly 200 miles northward. These hummingbirds can now reliably be found in winter from the Gulf Coast states up the Atlantic Coast to South Carolina.
To better understand the winter ecology of these hummingbirds at the northern edge of their new winter range, researchers intensively studied birds in one South Carolina backyard. They studied the birds passing through and wintering in the area for four years, gathering data on age, sex, and frequency of return. The research team banded 416 hummingbirds with minuscule identification rings, each with a specific sequence of numbers, so that individual birds could be identified. At the end of the study period, the researchers had accumulated interesting results.
The likelihood that an individual would return to the study site for more than one winter was about 19%, a higher return rate than what had been previously documented at study sites farther south. Among females, the return rate was even greater, reaching more than 31%. Some individuals returned every winter during the study period, while others returned only once or twice. None of the hummingbirds present during the winter lived in the area during the summer, suggesting that the summer residents had migrated south and the winter residents were from breeding populations farther north. Furthermore, during winter more males than females were present, especially among juvenile birds. This suggests that different sexes and ages winter in different places, a strategy used by many bird species, but a pattern not previously documented in Ruby-throated Hummingbirds.
The researchers predict that wintering Ruby-throated Hummingbirds will continue to move farther north as the climate continues to warm. Wintering closer to their breeding grounds not only increases their chances of surviving migration, but also allows them to start breeding sooner. Who knows? Maybe in a few decades we’ll never have to spend a winter without hummingbirds.
Reference: Cubie, D. 2014. Site Fidelity, Residency, and Sex Ratios of Wintering Ruby-throated Hummingbirds (Archilochus colubris) on the southeastern U.S. Atlantic Coast. The Wilson Journal of Ornithology 126: 775-778.
Lauren Flesher is senior at Cornell University studying sustainable agriculture. Her area of study includes the development of methods for avian conservation in agroecosystems, and the mitigation of avian pest damage.