The Anna’s hummingbird (Calypte anna) is a medium-sized hummingbird native to the west coast of North America. Known for its iridescent emerald and rose plumage, the Anna’s hummingbird is one of the most common backyard hummingbirds in its range. But does this colorful hummingbird migrate like many of its relatives?
Quick Answer
The answer is yes and no. Most Anna’s hummingbirds are permanent residents that don’t migrate. However, some populations do migrate short distances seasonally.
Anna’s Hummingbird Overview
With a body length of 3-3.5 inches and weight of 3-6 grams, the Anna’s hummingbird is slightly larger than other common hummingbirds like the ruby-throated hummingbird. The male Anna’s hummingbird has a distinctive iridescent rose-pink throat and crown, with emerald green back plumage. Females lack the colorful throat patch and are overall grayish-green in color.
The Anna’s hummingbird is named after 19th century collector Anna Massena. It was first classified by ornithologist John Gould in 1852 based on a specimen collected in Santa Barbara, California. At the time, it was thought the Anna’s was a subspecies of the Allen’s hummingbird. It wasn’t recognized as a full species until 1983.
The Anna’s hummingbird breeds from November to June and often raises two broods per season. The female builds a small cup-shaped nest out of plant down and spider webs, laying two tiny white eggs. Incubation lasts 14-19 days and the chicks fledge in another 18-23 days.
Year-Round Population
Most Anna’s hummingbirds living along the Pacific Coast do not migrate and instead maintain year-round territories. Their range extends along the coast from southern British Columbia to Baja California. In this region, abundant natural food sources allow the birds to survive the winter – there is no need to migrate elsewhere for food.
These resident Anna’s hummingbirds are trapliners, visiting a network of flower patches each day to feed. By not tying themselves to a single area, the birds can track sporadic blooms of different plants through the seasons. Winter-blooming plants like ribbonwood, cherry, currant, and manzanita provide essential sustenance when many flowers have finished blooming for the year.
The Anna’s hummingbird has also adapted well to urbanization and readily visits feeders and non-native garden flowers. This supplemental food from humans supports year-round populations even in areas like San Francisco with cool, rainy winters. Provided enough flowers and feeders are available, Anna’s hummingbirds can withstand cold temperatures and precipitation.
Seasonal Movements
Some northern and mountain populations of Anna’s hummingbirds do migrate short distances (under 500 miles) when food gets scarce in the breeding range. Migrants generally move to lower elevations or more southern latitudes after breeding.
In British Columbia, Anna’s hummingbirds nest as far north as Vancouver Island and the Gulf Islands. But most birds retreat south to winter along the coast or in northern Washington. Banding studies show birds summering on Vancouver Island fly as far as California in the winter.
Farther south in Washington, Oregon, and California, higher elevation breeding birds migrate downslope to escape severe winter weather. The birds summer in mountain meadows but winter in lower foothills and valleys. These movements are usually less than 125 miles.
Not all migrating Anna’s hummingbirds travel the same distances. It depends on the severity of the weather and available food supply. Some birds may only go far enough to escape freezing temperatures and snow. Banding data has recorded winter movements ranging from 35 miles to over 600 miles.
Fall Migration
The timing of fall migration for Anna’s hummingbirds depends on the breeding location:
- British Columbia: August to mid-October
- Mountain West: Mid-August to early November
- Pacific Coast: Late July to December
Young birds just fledged from the nest often migrate earlier than more experienced adult birds. The males and females generally migrate around the same time in the fall.
Spring Migration
In spring, the northbound migration happens over a broader time period:
- British Columbia: Mid-February to late May
- Mountain West: Early March to late May
- Pacific Coast: February to April
Adult males usually lead the way in spring, returning to the breeding grounds before the females. Early return gives the males an advantage in setting up the best territories.
How Do Anna’s Hummingbirds Migrate?
When migrating, Anna’s hummingbirds fly alone during both day and night. Their small size and high metabolism require frequent stops to rest and refuel. Males and females develop their own migration routes rather than traveling together.
Hummingbirds rely on specialized orientation instincts to navigate their biannual migrations. Scientists hypothesize they may orient themselves by the sun’s position, patterns of polarized light, or the earth’s magnetic field. Landscape features and smell may also aid navigation over familiar routes.
Fuels for Migration
To power their migratory flights, Anna’s hummingbirds feed on high energy nectar and small insects:
- Nectar – The main source of quick energy. Provides simple sugars.
- Insects – Essential source of fat and protein. Spider webs are also gathered for nutrients.
During migration, the birds need to build up fat reserves. Fat provides more energy per unit of weight than carbohydrates from nectar. Excellent vision and hovering ability allow hummingbirds to hunt insects mid-flight.
Rest Stops
Anna’s hummingbirds break up migratory trips with frequent rest stops, every 25-125 miles. At rest stops they spend time feeding intensely on nectar and insects to replenish energy. Some migration stopovers last a few days or longer if the habitat offers abundant food.
Suitable rest stops provide shelter from weather plus enough flowers, tree sap, and small insects to sustain the birds. The hummingbirds prefer meadows, yards, parks, and other open areas with adequate nectar supplies. Native plants like Indian paintbrush, larkspur, andsnapdragons draw in migrating Anna’s hummingbirds, as do non-native flowers like fuchsias.
Evidence of Migration
How do researchers know which Anna’s hummingbird populations migrate? Marking individual birds allows scientists to track seasonal movements. Banding and population surveys provide most of the migration data.
Banding
Hummingbird banding involves gently trapping the birds in small cages and then fitting a tiny numbered band around one leg. Banding provides identification so birds can be recognized if re-caught or recovered later. By banding birds at set nesting locations and then recapturing them at different wintering sites, biologists can map migration routes and distances.
For Anna’s hummingbirds, banding has revealed both migratory and non-migratory populations. In California, banded adult female Anna’s hummingbirds were found returning to the same wintering grounds each year. Yet banded birds in British Columbia turned up hundreds of miles away in California during winter.
Population Surveys
Comparing breeding season and winter season population surveys is another method used to study hummingbird migration. For the Anna’s hummingbird, breeding bird surveys indicate populations increase during summer in the mountain West and Pacific Northwest compared to winter totals. The surge in summer birds likely represents migrants arriving from southern wintering areas.
Christmas Bird Counts coordinated by citizen scientists also reveal winter movement patterns. For Anna’s hummingbirds, the counts show greater winter populations in California and the Southwest versus the Northwest – mirroring the southward shift for some migratory populations.
Climate Change Impacts
How might climate change affect Anna’s hummingbird migration? Warmer temperatures may allow the birds to expand their breeding ranges farther north. Harsher winters could force currently non-migratory populations to migrate. For birds that already migrate,climate change may shift the timing of movements.
Research in Arizona indicates Anna’s hummingbirds are migrating earlier in spring and delaying fall migration. From 1975 to 2000, the birds advanced spring arrival in Arizona by an average of 10 days. This matches trends seen in other species – earlier spring greenup of vegetation prompts earlier nesting. Delayed fall migration is likely a response to warmer weather and greater food availability later into the autumn months.
Threats from Climate Change
Although Anna’s hummingbirds may benefit from expanded range and longer nesting seasons, climate change also poses threats:
- Reduced summer water supplies in key breeding areas
- Increased risk of drought and wildfires damaging habitat
- Hotter summers taxing birds near their physiological limits
- Phenological mismatch between flowering plants and nesting
- Unfavorable weather events during migration
Researchers predict the Anna’s hummingbird’s breeding range will shrink by more than one-quarter by 2080 due to warming temperatures and drought. Climate models show increasing summer heat and water deficit decreasing suitability across the Southwest. This is concerning since the Southwest represents a large portion of the Anna’s current range.
Unique Traits for Survival
The Anna’s hummingbird has several behavioral and physiological adaptations to help it survive in both summer and winter environments:
- Cold tolerance – Drops body temperature and enters torpor to conserve energy on cool nights
- Heat resistance – Efficient evaporative cooling from rapid breathing prevents overheating
- Generalist diet – Feeds on wide variety of flower types, nectar and pollen
- Cognitive skills – Excellent spatial memory helps locate sparse and variable food sources
These traits equip the Anna’s hummingbird for life along the variable Pacific Coast climate as well as seasonal migration. The bird’s natural resilience indicates it may have some success adapting to the regional changes predicted under climate change. Supporting Anna’s hummingbirds by planting native flowers appropriate for warmer, drier conditions can further aid their populations.
Conclusion
In conclusion, the Anna’s hummingbird exhibits partial migration. Populations in the northernmost and highest elevation portions of the range migrate south and to lower elevations in winter. Further south along the Pacific Coast, Anna’s hummingbirds mostly do not migrate and instead maintain year-round territories. Climate change may induce greater migratory behavior as the climate warms. For all populations, providing sufficient flower nectar, insects, and clean water, whether through native plantings or artificial feeders, will support these charismatic hummingbirds through the seasons.
