Why do some hummingbirds not migrate?

Hummingbirds are well known for their annual migrations, with many species traveling thousands of miles between their breeding and wintering grounds. However, some hummingbird species and populations do not migrate at all and instead remain resident year-round in the same area.

Summary

Here are quick answers to key questions about non-migratory hummingbirds:

• Some hummingbird species like Anna’s and Allen’s hummingbirds have populations that are resident year-round in parts of their range.
• Factors like abundant food, suitable habitat, and moderate climates allow them to survive the winter in their breeding areas.
• They may minimize energy expenditure by going into nightly torpor and having smaller broods.
• Range expansions have allowed species like Anna’s hummingbird to colonize more northerly areas.
• Climate change may further facilitate range expansions as winters become milder.

Reasons Some Hummingbird Populations Do Not Migrate

There are several key reasons why certain hummingbird species and populations are able to reside year-round in areas where others migrate away for the winter:

• Sufficient food resources – Access to adequate nectar and insect food sources throughout the year allows resident hummingbirds to meet their high metabolic demands.
• Moderate climates – Milder climates reduce thermoregulation challenges and lower metabolic costs for overwintering.
• Behavioral and physiological adaptations – Entering torpor at night and having smaller broods in the breeding season helps minimize energy expenditures.
• Expanding ranges – Warming climates have facilitated range shifts, allowing species like Anna’s hummingbird to colonize more northerly wintering grounds.
• Urban habitats – Gardens, parks, and feeders in urban and suburban areas provide food and shelter.
• Lack of migratory instinct – Some populations may simply lack the inherent drive to migrate seasonally.

Examples of Non-Migratory Hummingbird Species

Some specific hummingbird species with resident populations that do not migrate include:

Anna’s Hummingbird

• Native to the Pacific Coast, it is one of the most northerly distributed hummingbirds.
• Introduced to areas like British Columbia and Washington, where populations are now permanent residents.
• Sufficient natural food and increasing urban feeders allow year-round residency.

Allen’s Hummingbird

• Coastal California and Pacific Northwest populations are non-migratory.
• Mild climate and abundant food sources allow winter residency.
• May enter torpor to conserve energy on cold nights.

Rufous Hummingbird

• Though mostly migratory, some Pacific Northwest and Alaska populations overwinter.
• Access to feeders critical during winter months.

Buff-bellied Hummingbird

• Native to Mexico, small populations now resident year-round in Texas.
• Attracted by winter-blooming flowers and urban feeders.

Ecological Factors Facilitating Residency

Several ecological and climatic factors make it possible for some hummingbird populations to forego migration and take up year-round residency:

Abundant Food Resources

Access to plentiful nectar sources and adequate insect prey allows resident hummingbirds to meet their high metabolic needs throughout the year.

Urban Habitats

Gardens, parks and artificial feeders concentrate food resources, providing critical winter support.

Moderate Winter Climates

Milder climates decrease thermoregulation costs and reduce risk of starvation from cold exposure.

Microclimates

Hummingbirds may seek out favorable microclimates within their range, moving altitudinally to avoid extremes.

Physiological Adaptations

Entering torpor overnight and having smaller broods minimizes energy demands.

Limited Migratory Instinct

Some populations may lack the inherent drive or orientation mechanisms to migrate seasonally.

Advantages of Residency Over Migration

There are some key advantages resident hummingbirds gain over migratory populations:

Lower mortality – Avoid risks associated with migration such as starvation, predation, and collisions.

Earlier breeding – Can start nesting earlier than migratory birds returning to breeding grounds.

Reduced competition – Residents have exclusive access to resources in their territory during winter months.

Year-round territory – Can maintain and defend high-quality territories and food sources.

Lower energy costs – Save energy from not migrating long distances seasonally.

Less stress – Avoid physiological stresses associated with long migrations.

So by avoiding migration, resident hummingbirds can enhance survival, breeding success, and access to resources. These benefits promote stable, year-round populations.

Trends and Threats

Some current trends related to non-migratory hummingbirds include:

Climate change – Warming temperatures may allow further winter range expansions. However, climate extremes could threaten food supplies.

Urbanization – More bird feeders and gardens provide habitat but also increase hazards.

Pesticides and pollution – Environmental contaminants put hummingbirds at risk due to chemical sensitivities.

Habitat loss – Development destroys natural areas, countered by increasing gardens.

Competition – Invasive species may compete with hummingbirds for food and nest sites.

Careful monitoring is needed to understand how environmental changes influence overwintering hummingbird populations. Maintaining natural areas and reducing pesticide use can support their year-round residency.

Conclusion

While most hummingbirds migrate seasonally, some species like Anna’s and Allen’s have populations that reside year-round within their breeding range. Mild climates, sufficient food supplies, access to feeders, and adaptations like torpor allow these hummingbirds to survive the winter and gain advantages over migratory populations. However, habitat loss and climate change threaten the future of these overwintering populations. Continued research and habitat conservation will help ensure the success of non-migratory hummingbirds.