Hummingbirds are energetic creatures, constantly burning fuel to power their rapid metabolism and hovering flight. Maintaining a body temperature over 100 degrees Fahrenheit requires a constant caloric intake. They must consume roughly their own weight in nectar and insects daily. When winter cold dramatically reduces natural food sources, these tiny birds must employ strategies to survive the season. For the majority of species, this means embarking on long avian journeys.
The Necessity of Migration: Travel Routes and Timing
Most North American hummingbirds, such as the Ruby-throated and Rufous, undertake long-distance migrations to warmer regions to solve winter food scarcity. The Ruby-throated Hummingbird breeds across the eastern U.S. and Canada, departing between August and September for wintering grounds in southern Mexico and Central America. This journey often requires a non-stop flight of up to 2,000 miles, with many crossing the Gulf of Mexico. The Rufous Hummingbird breeds in the Pacific Northwest and Alaska, performing a longer migratory circuit of nearly 4,000 miles. Both species must double their body mass before departure to store the fat reserves that fuel these flights.
Surviving the Cold: The Torpor State
For migrating species or any hummingbird facing a sudden cold snap, survival depends on a physiological adaptation called torpor. Torpor is a temporary, deep state of inactivity that significantly lowers the bird’s energy expenditure, similar to a nightly mini-hibernation.
A hummingbird’s normal daytime body temperature of over 100 degrees Fahrenheit can drop by as much as 50 degrees during deep torpor. This dramatic temperature reduction slows biological functions, allowing the metabolic rate to decrease significantly. The heart rate, which exceeds 500 beats per minute while resting, may drop to fewer than 50 beats per minute. To wake up, the hummingbird generates heat internally through arousal, rapidly vibrating its flight muscles to warm its blood supply and regain full function.
Regional Differences: Where Some Stay Put
While most species migrate, a few, notably the Anna’s Hummingbird along the Pacific Coast, are year-round residents, even in the northern Pacific Northwest. Their ability to forgo migration is due to milder coastal climates and the availability of non-native, winter-blooming flowers often found in suburban environments. Anna’s Hummingbirds still rely on torpor to survive the coldest nights, but they also adapt their diet. In addition to nectar, they actively forage for small insects for protein and nutrients. They may also use sap wells created by sapsucker woodpeckers as a supplemental source of sugar water.
Providing Winter Resources
Readers who wish to support wintering hummingbirds must ensure that any resources provided are safe and consistently maintained. The correct nectar solution is a simple mix of one part white table sugar to four parts water, which should be boiled and cooled before use. Avoid adding red dye, honey, or any sugar substitutes, as these can be harmful to the birds.
Preventing the sugar water from freezing is a primary concern in cold weather. This can be accomplished by rotating two feeders, using commercial heating elements, or wrapping the feeder with insulated material. Feeders must also be cleaned regularly, ideally with a mild solution of white vinegar and water, to prevent the growth of mold and fungi.