The Broad-tailed Hummingbird (Selasphorus platycercus) is a small, colorful bird found in the western United States during the spring and summer months. In the fall, as temperatures drop and food sources become scarce, these hummingbirds embark on a remarkable journey south to their wintering grounds in Mexico.
Hummingbirds are well known for their incredible flying abilities. Their tiny bodies and fast-beating wings allow them to hover in midair and fly backwards or upside down. This makes them perfectly adapted for the long migration flights they undertake each year. For the Broad-tailed Hummingbird, the journey south can cover over 3,000 miles as the birds travel from breeding grounds as far north as Wyoming and Montana to winter habitats in central and southern Mexico.
Understanding where these tiny birds go each winter has long fascinated ornithologists and bird enthusiasts. By tagging individual birds with trackers and conducting field observations across the western U.S. and Mexico, scientists have pieced together details on the migration routes and overwintering areas used by Broad-tailed Hummingbirds.
Fall Migration
Broad-tailed Hummingbirds begin leaving their breeding grounds as early as late July, though the peak migration period occurs between mid-August and early September. The timing likely depends on a mix of factors including food availability, weather conditions, and hormonal changes.
As they prepare to migrate, Broad-tailed Hummingbirds enter a period of hyperphagia where they consume extra calories to store fat for the long journey ahead. A bird’s pre-migratory weight gain can increase its body mass by over 40% in some cases. This additional fat provides critical energy reserves that allow the tiny birds to fly for extended periods without stopping to feed.
To fuel up, Broad-tailed Hummingbirds seek out food-rich mountain meadows and forest openings that provide nectar from late-blooming flowers such as red columbine and trumpet gentian. They also consume more insects during this period as a source of fat and protein.
Once migration commences, the Broad-tailed Hummingbirds head south following mountain ranges such as the Rocky Mountains in a meandering path. The birds make frequent stops to rest and refuel, visiting a succession of high-elevation flower meadows along the way.
Researchers have discovered key migration stopover sites in places like the Gila National Forest in New Mexico, the Huachuca Mountains in Arizona, and the Chiricahua Mountains between Arizona and New Mexico. At these oases, the tiny travelers find plenty of food to sustain them on the next leg of their journey.
The Broad-tailed Hummingbirds fly during the day, traveling anywhere from 25 to 300 miles at a time depending on wind conditions and the availability of stopover habitat. While they typically fly close to the tree canopy, some impressive feats have been recorded, such as a female Broad-tail that was tracked flying nonstop over the Gulf of Mexico at an altitude of 1800 feet!
At night, the birds conserve energy by entering torpor, a state similar to hibernation where their metabolic rate and body temperature drop. They roost in trees and rely on their camouflaged plumage to hide from potential predators.
Arrival on the Wintering Grounds
The majority of Broad-tailed Hummingbirds complete their fall migration by mid-October, arriving on their wintering grounds in the highland forests of central Mexico.
Research by scientists who attached geolocators to migrating Broad-tailed Hummingbirds shows that the birds travel to and winter in the Transverse Volcanic Belt region that spans several Mexican states including Michoacán, México, Puebla, Veracruz and others.
Within this volcanic mountainous area, the hummingbirds seek out pine and pine-oak forests at elevations between 5,000 and 9,500 feet where flowers are still abundantly blooming. Favorite winter locations include forest clearings, canyon slopes, and the edges of mountain meadows.
The hummingbirds aggressively defend small territorial feeding areas against intruders once they arrive. The abundance of flower nectar in their winter habitat means they no longer have to conserve energy through torpor and can actively feed throughout the day.
Some research indicates there may be differences in migration timing and wintering sites based on a bird’s age and sex. For example, adult males appear to arrive earlier on the wintering grounds to claim prime habitats. Immature birds and females migrating with young hatchlings may winter farther south in locations like El Salvador and Honduras.
The Wintering Period
Broad-tailed Hummingbirds spend roughly half the year, from October through March, at their wintering sites in Mexico.
This winter period is a time of relative stability after the huge exertion of migration. The hummingbirds mate on the wintering grounds and females build up reserves in preparation for the energetically expensive nesting season.
Their habitat preferences during winter put them in proximity to a number of bird species that nest in the same pine-oak forests during the summer months. These include species such as the Painted Redstart, Red-faced Warbler, Red Warbler, and others.
One advantage of wintering in Mexico’s highlands is relatively mild weather compared to the freezing temperatures farther north. However, nights are still quite cold. To conserve heat, Broad-tailed Hummingbirds enter nightly torpor once again, allowing body temperature and metabolism to fall. They may also nestle into cavities in trees or cacti for added insulation while roosting.
In terms of food, the hummingbirds rely on any flowers still blooming in the dry winter months, visiting favorites like thistle, fuchsia, and poinsettia. They also feed heavily on small arthropods when flower nectar is scarce. Various species of gnats, midges, and small flies provide an abundant protein source.
By migrating south, Broad-tailed Hummingbirds escape the harshest weather and find adequate food to see them through until spring. While the winter period represents a break from breeding activities, the hummingbirds still face threats like predation. Merlins and other falcon species hunt the hummingbirds, as do jays and roadrunners. Mites and lice may also infest their plumage during the winter.
Return Migration in Spring
As days lengthen in late February and March, Broad-tailed Hummingbirds once again become restless to migrate north. The males typically begin migrating first, followed by the females one to two weeks later.
The return trip brings unique challenges as the hummingbirds must fly into prevailing winds and weather patterns. Nevertheless, their stopover sites and routes generally mirror the path used in autumn, just in reverse sequence.
One difference in spring is the importance of timing arrival on the breeding grounds with flower blooms. By migrating in February and March, the Broad-tailed Hummingbirds reach northern meadows right as key nectar plants like Indian paintbrush and larkspur begin flowering.
The arrival period extends from mid-March through May depending on the latitude. Males reach the breeding areas first, while females tagged with trackers have been observed stopping over for up to 10 days to feed extensively and await ideal conditions before the final push.
With precise timing and ample food resources, the hummingbirds are ready to breed as soon as they complete this epic round-trip migration. The wintering period gives them a chance to rest and build critical energy stores before the breeding season gets underway. For researchers, answering questions about where these tiny travelers spend their winters provides one more piece of the puzzle in the remarkable life history of Broad-tailed Hummingbirds.
Key Facts
Broad-tailed Hummingbird Winter Migration
- Migrates between breeding grounds in the western U.S. and Mexico
- Fall migration from late July through mid-October
- Fly during day, rest and enter torpor at night
- Stopover sites located in mountains along the route
- Build up fat reserves by eating more nectar and insects before migrating
- Fly 25-300 miles between stopover sites
Winter Range and Habitat
- Primarily the Transverse Volcanic Belt of central Mexico
- Pine and pine-oak forests at 5,000-9,500 ft elevation
- Forest clearings, canyon slopes, mountain meadow edges
- Milder weather than northern breeding range
Winter Ecology and Behavior
- Defend small feeding territories
- Mate on wintering grounds
- Build up reserves for future breeding
- Eat flowers, nectar, arthropods
- Enter nightly torpor to conserve energy
- Face threats like falcon predation
Spring Migration
- Males leave first in late February/March
- Females follow 1-2 weeks later
- Time arrival on breeding grounds with flower blooms
- Route mirrors fall migration
- Arrive on breeding areas mid-March through May
Conclusion
In conclusion, Broad-tailed Hummingbirds migrate incredible distances each year between their breeding homes and wintering grounds. By banding birds and tracking their movements, scientists have gained insight into the migration timing and routes, habitats used along the way, and winter behavior of these tiny travelers.
Key findings show that the hummingbirds wing their way south along mountain ranges from late summer through fall, fueling up at flower-rich stopover sites. They spend the winter in pine-oak forests of central Mexico where they find adequate food and escape freezing temperatures. Mating, building energy reserves, and entering torpor to conserve energy occupy them until the return trip north in spring. Their yearly journey is an amazing feat of endurance for a bird that weighs less than a nickel. Unlocking the migration secrets of Broad-tailed Hummingbirds provides inspiration and insight into the natural world.