Hummingbirds are some of the most fascinating birds in the world. Their ability to hover mid-air and drink nectar while beating their wings up to 80 times per second is mesmerizing to watch. But something that perplexes many hummingbird enthusiasts is why these birds seem to suddenly appear and then disappear again from feeders and gardens.
What causes hummingbirds to migrate?
Hummingbirds are migratory birds that travel vast distances every year between their summer breeding grounds in North America and their overwintering grounds in Mexico and Central America. There are several factors that trigger hummingbird migration each season:
- Declining food sources – As flowers begin to fade and nectar becomes scarce in late summer and fall, hummingbirds are prompted to travel south where nectar-rich flowers are still abundant.
- Changing temperatures – Hummingbirds have high metabolisms and struggle to meet their high energy needs in colder temperatures when fewer flowers and insects are available. They migrate to warmer tropical climates in winter.
- Hardwired instinct – Even hummingbirds raised in captivity exhibit restless behavior and a drive to migrate when summer ends. This suggests migration is an innate behavioral pattern in hummingbirds, triggered by environmental cues.
These factors initiate an incredible migration each fall as hummingbirds depart their breeding grounds and journey hundreds or thousands of miles to their winter homes. Ruby-throated hummingbirds may travel across the Gulf of Mexico, a 500-mile nonstop flight over open water. Rufous hummingbirds migrate up to 3,900 miles one-way from Alaska to Mexico.
When do hummingbirds migrate?
Hummingbird migration timing follows a predictable seasonal pattern:
- Early spring – Most hummingbirds begin arriving back at their northern breeding ranges in March and April as flowers start to bloom.
- Late summer – Adult hummingbirds and their offspring begin migrating south in August and September.
- Fall – Migration peaks in late August through October as food declines and temperatures drop.
- Winter – The few hummingbird species that remain year-round in the U.S. hunker down in November and December when food is most scarce.
- Late winter – Southward migration ends by late December or January when most hummingbirds have arrived at their tropical wintering grounds.
The exact timing varies by species and location. But this general timeline is why hummingbirds seem to suddenly vanish from one area and show up in another almost overnight in spring and fall. Their migration is a rapid transit between seasonal homes guided by food availability, temperatures, and other environmental cues.
Where do hummingbirds go in winter?
When hummingbirds disappear from their northern breeding range each fall, they migrate south to overwinter in specific regions:
- Ruby-throated – Southern Mexico to Panama
- Rufous – Mexico
- Allen’s – Mexico
- Anna’s – Pacific Coast down to Mexico
- Black-chinned – Mexico
- Calliope – Mexico
With hundreds of hummingbird species and subspecies that all migrate and winter in distinct regions, it can be challenging to track exactly where each individual bird travels. Banding programs where tiny aluminum leg bands are placed on hummingbirds provide helpful migration data. One banded ruby-throated hummingbird was tracked traveling between Michigan and Costa Rica over multiple winters.
Why do some hummingbirds not migrate?
Most hummingbirds migrate every spring and fall between temperate breeding habitats and tropical climates. However, some exceptions exist:
- Anna’s hummingbird – A year-round resident along the Pacific Coast and southern Arizona where winter temperatures remain mild and food is adequate.
- Rufous hummingbird – Up to several thousand remain along the southeastern U.S. Gulf Coast where winter temperatures are warm enough to sustain them.
- Calliope hummingbird – Very small numbers may overwinter in sheltered microclimates along southern California and Arizona’s coast.
These non-migratory groups suggest that hummingbirds are opportunistic and may adapt their migration patterns over time based on sufficient food supplies and warm temperatures. Climate change could potentially enable more species to overwinter farther north instead of migrating long distances.
How do hummingbirds know when to migrate?
Hummingbirds appear to rely on a mix of external cues and internal programming to initiate seasonal migrations at precisely the right time:
- Photoperiod – Changing day lengths register in their brains to signal the time for migration. Hummingbirds begin molting and building fat stores when days start shortening in late summer.
- Food availability – Declines in flower nectar and insects motivate hummingbirds to seek out new food sources.
- Weather patterns – Cues such as falling temperatures, rain, and winds provide additional information that winters are approaching.
- Circadian rhythms – Hummingbirds have internal clocks and seasonal cycles genetically programmed to guide migrations.
- Orientation – They can sense geomagnetic fields to help orient themselves during travels between seasonal sites.
Research indicates hummingbirds integrate many different external cues with internal circadian and circannual biological rhythms finely tuned by natural selection to keep their migration timing on schedule. They then exhibit an innate drive and orientation to embark on these epic seasonal journeys.
How do hummingbirds navigate migration?
Hummingbirds have specialized physiological and behavioral adaptations that enable them to accomplish miraculous long-distance migrations:
- Compasses – They can detect magnetic fields and use the sun for orientation during migration.
- Fuel efficiency – Their tiny size, streamlined shape, and highly efficient wings minimize energy needs in flight.
- Fat stores – Pre-migration gorging enables hummingbirds to double their weight, adding fat stores to fuel migration.
- Torpor – Periodic torpor states allow hummingbirds to conserve energy on migration when not actively flying.
- Navigation – They appear to use mental maps, landmarks, and other cues to navigate their way between seasonal sites.
These specialized adaptations make hummingbirds champion migrants capable of navigating thousands of miles between their seasonal homes. Their ability to determine location, direction, and favorable routes is still not fully understood but clearly involves a complex integration of their senses, internal guidance systems, experience, and environmental cues.
How do hummingbirds know where to migrate to?
Hummingbirds likely identify their migratory destinations through some combination of the following:
- Instinct – They exhibit innate drive and direction to migrate to ancestral wintering grounds they’ve never visited.
- Genetics – Migration routes and timing are programmed into their DNA over thousands of generations.
- Learning – Young hummingbirds may learn routes by traveling with experienced adults their first migration.
- Experience – Hummingbirds remember landmarks and map out routes between seasonal sites after previous trips.
- Smell – Odors may provide olfactory maps to guide hummingbirds across oceans and other barriers.
Research shows hummingbirds can orient along migration routes even if displaced far from the course. Clearly, an innate guidance system directs them to pre-determined wintering regions each season. But learning, memory, and odor cues likely help hummingbirds refine routes and target destinations over successive migrations.
Conclusion
In summary, several key factors explain the seasonal disappearance and reappearance of hummingbirds:
- They migrate huge distances between temperate breeding and tropical wintering grounds following ancient routes encoded in their DNA.
- Environmental cues such as food availability, temperature, and photoperiod trigger migration instincts at precise times.
- Specialized adaptations allow hummingbirds to accomplish miraculous migratory feats between seasonal homes often thousands of miles apart.
- Navigation involves a complex integration of genetics, learned mental maps, sensory capabilities, and orientation mechanisms that guide hummingbirds along established routes.
While many details remain mysteries, scientists are gradually revealing how hummingbirds orchestrate these extraordinary seasonal migrations with such accuracy and timing. Unraveling these secrets further can help inform conservation efforts for these captivating birds as their habitats and migratory journeys face growing threats in today’s world.
