Why do some hummingbirds migrate and others don t?

Hummingbirds are found naturally only in the Americas. Of the over 300 species of hummingbirds, some migrate seasonally while others are year-round residents in their breeding range. The factors that determine whether a species migrates or not includes food availability, climate, competition, and evolutionary adaptations.

What is bird migration?

Bird migration refers to the regular, seasonal travel of bird species from one region to another to find more favorable conditions for feeding and breeding. Migration allows birds to take advantage of abundant seasonal food resources and breeding habitats. Many species migrate north in the spring to take advantage of longer daylight hours and the surge in insect populations. In the fall, they migrate south to warmer climates with adequate food supplies.

Why do some hummingbirds migrate?

Hummingbirds migrate for a variety reasons related to resources and survival:

• Food availability – Nectar from flowers is the main food source for hummingbirds. Some species migrate to follow the bloom period of flowers and shrubs and to take advantage of new nectar sources. The availability of flower nectar and small insects is strongly influenced by seasonal weather patterns.
• Climate – Many hummingbirds cannot survive cold winters and freezing temperatures. Species like rufous hummingbirds and ruby-throated hummingbirds migrate south to warmer climates in Mexico and Central America where they can find enough food and don’t need to deal with extreme cold.
• Breeding – Some species migrate north in spring to take advantage of longer daylight hours and the abundance of flower nectar and insects, which allows them to breed and nest successfully.
• Competition – In tropical areas, there is more competition year-round among hummingbird species for limited food resources. This may have driven some species to evolve migratory behavior to take advantage of seasonal food resources elsewhere.

Why do some hummingbirds not migrate?

Here are some key reasons why some hummingbird species do not migrate:

• Adequate year-round food – In tropical regions there are flowering plants and adequate insect populations for food year-round, allowing some hummingbirds to establish permanent residency.
• Moderate climate – Species like Anna’s hummingbird and Allen’s hummingbird live along the Pacific coast where the climate is mild year-round, allowing them to survive winters without migrating.
• Elevational migration – Some tropical highland species move up and down mountain slopes to follow flower blooms at different elevations, avoiding the need to long-distance migrate.
• Evolutionary adaptation – Resident hummingbirds have evolved adaptations like torpor (temporary reduction in activity and metabolism) to help them survive periods of resource scarcity.

Different migration strategies

Not all migratory hummingbirds have the same migration patterns and strategies. Here are some of the key differences:

The farther north a species breeds, the more likely it is to migrate long distances south. Ruby-throated hummingbirds nest as far north as Canada and undertake a 2,000 mile migration to Central America.

Western hummingbirds like rufous hummingbirds migrate medium distances north and south following flower blooms. Tropical mountain species like the white-eared hummingbird may only move a few miles up or down in elevation seasonally.

In some species like the calliope hummingbird, northern populations migrate south while southern populations remain year-round residents. Migration distance depends on how far they need to travel to find suitable habitat conditions.

Physiological adaptations for migration

Hummingbirds have many physiological adaptations that allow them to fly long distances during migration:

• Lightweight – Hummingbirds weigh only 2-20 grams. Their small size helps minimize energy needs during flight.
• Hovering ability – They can hover and fly backwards, which helps them take advantage of any food source during migration.
• Fat stores – They build up fat reserves equal to 30-50% of their body weight to provide energy for migration.
• Rapid metabolism – Their rapid heartbeat and breathing allow them to metabolize fat quickly to fuel energetic flight.
• Aerodynamics – Their streamlined body and wing shape make them very aerodynamically efficient fliers.

These adaptations allow hummingbirds to fly hundreds of miles nonstop over land, deserts, mountains, and even the Gulf of Mexico during their seasonal migrations.

Navigation ability

One of the most remarkable things about hummingbird migration is their ability to navigate over vast distances between their breeding and wintering grounds. They use a combination of physiological cues:

• Mental map – They have an internal magnetic compass and mental map to chart their migration route based on landscape features.
• Celestial cues – They use the sun and patterns of polarized light for guidance during daytime migration.
• Stars – On clear nights they can orient themselves using stars.
• Landscape – They use mountains, coastlines and other landmarks for navigation during migration.

Young birds likely imprint on the migration route and celestial cues their very first journey with guidance from experienced adults. They can find their way back to the same wintering sites each year through their mental map and compass system.

Threats faced during migration

Hummingbirds face many hazards and threats during their seasonal migrations including:

• Lack of food/habitat along migration route
• Inclement weather – storms, wind, rain, cold temperatures
• Predators – Hawks, falcons
• Collisions with buildings and structures
• Exhaustion and starvation

Up to 50% of birds die during their first migration. Hummingbirds benefit from traveling in loose flocks during migration for protection. Stopover habitats along migration routes with adequate food are critical for them to rest and refuel. Urban development that destroys stopover habitats places migrating hummingbirds at greater risk.

Impact of climate change

Climate change could impact hummingbird migration in some of the following ways:

• Flower and food source availability changing in their breeding and wintering grounds
• Mismatch between migration timing and flower blooming
• Hotter temperatures causing dehydration and heat stress
• Stronger storms disrupting migration routes
• Drying of stopover habitats along migration route

Hummingbirds may need to shift their migration timing and routes to match up with new resource availabilities created by climate change. More research is needed to understand how climate change will impact different hummingbird species and their migratory behaviors.

Importance of migration

Seasonal migration is critically important for hummingbirds for the following reasons:

• Allows them to breed in highly seasonal northern habitats with abundant summer food resources
• Gives them access to warmer climates with adequate food in winter
• Reduces competition for limited resources by moving to take advantage of seasonal booms
• Enablesescape fromextreme weather conditions and freezing temperatures
• Provides access to a wider diversity of food sources throughout the year

Without migration, most hummingbird species would not be able to survive or effectively reproduce. Their small size and high metabolism requires taking advantage of seasonal food resources across a variety of habitats and climate zones.

Unique aspects of hummingbird migration

Hummingbird migration has some unique characteristics compared to migration in other birds:

• Small body size – The smallest bird to complete long-distance migrations
• Hovering flight – Allows them to take advantage of any flower nectar source
• Fat storage – Up to 50% of body mass stored as fat fuel
• Rapid metabolism – Fast heartbeat enables fat burning mid-flight
• Backward flight – Helps maximize nectar intake from flowers
• Torpor – Reduced body temperature and metabolism to conserve energy
• solo travelers – Most species migrate individually rather than in flocks

These traits enable their long-distance migration despite the challenges posed by their tiny size and high energy needs. No other migratory bird can match the energetic demands that tiny hummingbirds achieve during their seasonal travels.

Research techniques

Scientists study hummingbird migration using some of the following key techniques:

• Banding – Tiny numbered bands placed on legs to identify individual birds and date and location they are spotted
• Radio telemetry – Tiny radio transmitters attached to track migration routes
• Stable isotope analysis – Chemical analysis of feathers to determine geographic areas birds originated from
• Citizen science – Bird watchers report hummingbird sightings to projects like eBird and Journey North
• Doppler radar – Detects movement of birds during migration events

Advances in miniaturization of tracking technology have allowed more detailed study of individual hummingbird migrations. Combining multiple techniques provides the most complete picture of their migration timing, routes, distances, and connectivity between populations.

Conservation importance

Protecting hummingbird migration is an important conservation priority for the following reasons:

• Prevent declines of species that migrate long distances
• Maintain genetic connectivity between populations
• Provide adequate stopover habitat along migration routes
• Understand impacts of climate change on migration patterns
• Educate public about threats faced by migrating birds

Partners in Flight estimates that over 40% of hummingbird species in North America are declining. Conservation strategies focused on protecting habitats along their entire migration route are crucial to stabilizing and recovering hummingbird populations.

How to help hummingbird migration

Here are some ways that people can help support hummingbird migration:

• Provide nectar feeders for food at stopover sites
• Plant native flowers and shrubs that bloom through the migration seasons
• Avoid pesticide use which reduces insect food supplies
• Keep cats indoors to reduce predation on migrants
• Participate in citizen science projects to track migration timing and movement
• Support habitat conservation of protected lands used during migration

Even simple actions by homeowners like providing sugar water, reducing pesticide usage, and planting a diversity of native plants can make a difference for migrating hummingbirds.

Conclusion

The phenomenon of hummingbird migration provides unique insights into the ecology, physiology, and conservation of these specialized nectar-feeding birds. Their migratory habits have evolved to take advantage of seasonal food resources across a variety of habitats and climate zones. Ongoing research continues to reveal the remarkable capabilities of hummingbirds to navigate and sustain energetic flight over immense distances during their migrations. Maintaining healthy landscapes along their migratory routes is crucial to ensuring that these iconic New World migrants can continue their extraordinary seasonal journeys for generations to come.