It might be small, but the ruby-throated hummingbird sure is mighty. Spending their summer in the eastern United States where they breed, every year the little birds migrate thousands of kilometers south to spend the winter in Central America. They manage this despite weighing in at just 2 to 6 grams (0.07 to 0.2 ounces) each and measuring only 8 centimeters (3 inches) long. Now, a new study has examined the intricacies of this epic flight from this minuscule bird.
The ruby-throated hummingbird is the most common hummingbird found east of the Mississippi river, but it is not a year-round resident. Every winter they embark on a monumental migration from as far north as Canada where they breed, to as far south as Panama where some of the birds winter. and it turns out that some of them could potentially do it without stopping. Researchers trapped and tagged 2,729 birds as they passed through the southern state of Alabama between late August and late October over a 5-year period, and have built on previous knowledge about their epic migration.
What they found was that older hummingbirds tended to get on their travels earlier, which they think is due to the birds being more experienced and socially dominant. “It's interesting that the young of the year migrate after adults and are quite different in their stopover phenology,” explains Chris Clark, who coauthored the paper published in The Auk: Ornithological Advances. “This suggests there are substantial differences between flying south for the first time, as opposed to flying somewhere again as an adult.”
Based on morphometric data – such as size and weight – collected on the little creatures, the team also predict that the older and male birds are probably also able to travel farther than those on their maiden migration and the females. The wing shapes of the males were significantly different when compared to the females, being shorter and more tapered, which increases their maneuverability, and according to the researchers would permit them to travel as far as 2,200 kilometers (1,367 miles) without stopping.
“The most interesting thing, in my opinion, is how some of these birds effectively double their body mass during migration and are still able to perform migratory flights, especially given some of the heftier birds seem to barely make it to a nearby branch after being released,” says Theodore Zenzal, another of the coauthors. For such a small bird, even just a single gram (0.035 ounces) of extra body weight, which is equivalent of an average human who weighs 60 kilograms (132 pounds) putting on an extra 20 kilograms (44 pounds), will make all the difference on whether or not they make the migration.
But there are still questions to be answered. While we know that the little birds are able to fly such massive distances without a break, it is still unknown whether or not they take the most direct route by crossing the Gulf of Mexico, or skirt around the edge. The researchers would also like to delve further into the differences in the migratory behavior between the older and younger birds, and what decisions the age groups make.