As fall approaches and most hummingbirds migrate south, some hardy individuals make the decision to tough out winter in their breeding grounds rather than make the long journey. This phenomenon piques the interest of many birders and scientists alike. In this article, we’ll explore the key factors that motivate some hummingbirds to stay behind when others head to warmer climates.
Key Reasons Some Hummingbirds Stay Behind
There are a few primary reasons why certain hummingbirds decide to stick it out in their summer breeding territories even as temperatures drop:
- Availability of food – Some hummingbirds are willing to endure the cold if there are enough energy-rich food sources available. Feeders stocked by humans and ornamental flowers that bloom into fall and winter can help sustain them.
- Territoriality – Male hummingbirds are very territorial and may stay behind to defend a prime feeding territory. Their evolutionary drive to mate and pass on their genes may override their instinct to migrate.
- Age and size – Older, larger hummingbirds are better equipped to survive cold conditions. Younger ones and smaller species are more likely to migrate.
- Changing climate – Warmer fall and winter temperatures due to climate change allow more hummingbirds to overwinter in regions further north than they historically did.
Next, let’s go into more detail on each of these key factors influencing some hummingbirds to stick around on their breeding grounds through the winter.
Availability of Food Sources
Access to adequate nutrition is one of the most important considerations for hummingbirds when deciding whether to migrate or not. Hummingbirds have very high metabolisms and must consume up to half their body weight in nectar each day to survive. They are also at risk of starving to death if they go more than a few hours without feeding.
In the wild, hummingbirds meet their extreme nutritional needs by feeding on nectar from flowers. However, many of these natural nectar sources disappear in the fall and winter as blossoms fade. Some hummingbirds choose to migrate south rather than face scarce food. But others are willing to tough it out in their breeding grounds if some flowers are still in bloom or feeders are available.
Certain fall-blooming flower species like lantana, fuchsia, petunia, and snapdragon provide critical fuel for hummingbirds staying behind. Backyard bird feeders also enable northern hummingbirds to make it through harsh winters. A constant supply of fresh sugar water simulates the natural nectar they depend on.
With the right man-made food sources available, a hummingbird’s odds of surviving a northern winter and avoiding a long migration improve. Access to adequate nutrition outweighs cold temperatures and inclement weather for some individuals.
Key Winter Flower Species for Hummingbirds
Flower | Bloom Time | Color |
---|---|---|
Lantana | Summer to Fall | Red, yellow, orange, pink |
Fuchsia | Summer to Fall | Pink, purple, red |
Petunia | Spring to Fall | Variety of colors |
Snapdragon | Spring to Fall | Variety of colors |
Territoriality
Hummingbirds are very territorial, especially mature males. They become possessive of feeding areas that provide adequate nutrition. Sometimes this territorial nature outweighs their migratory instincts.
By staying behind on their breeding grounds, male hummingbirds can maintain prime real estate instead of returning in spring to find their old territory occupied. Their competitive evolutionary drive to secure food, attract females, and reproduce may override their motivation to migrate.
There is also evidence that hummingbirds remember feeder locations from previous seasons and will return to defended areas. This offers another incentive for certain individuals to stay put instead of migrating and having to reestablish food sources in spring.
However, staying behind does introduce risks for territorial male hummingbirds. They become vulnerable to freezing nights and icy storms. And if an adequate food source disappears, they can face fatal consequences.
Territorial Behavior of Male Hummingbirds
- Aggressive chases and attacks on intruders
- Vocalizations and display dives to ward off competitors
- Little energy spent on self-maintenance when defending territory
- Increased risk-taking, including flying in poor weather
Age and Size
An individual hummingbird’s age and size also factor into its decision to migrate or overwinter in its breeding territory. Older, larger hummingbirds are better equipped to withstand challenging northern winters compared to younger ones.
With age comes experience and resourcefulness. Older hummingbirds know to conserve energy on cold nights by entering torpor. This is a hibernation-like state where their metabolic rate and body temperature drop. Younger hummingbirds have not yet mastered torpor and are more vulnerable in winter.
Larger species like ruby-throated hummingbirds have a thermal advantage and can store more fat to get through long periods of inactivity when flowers are not blooming. Tiny species like calliopes are better off migrating south where they can actively feed year-round.
While tiny calliopes and other small species migrate almost universally, larger varieties like rufous and Anna’s hummingbirds are regular overwinterers in the north. Their greater size and fat storage make winter survival possible, especially with flower buds and artificial feeders providing nutrition.
Hummingbird Species Most Likely to Overwinter
Species | Average Mass | Overwintering Frequency |
---|---|---|
Rufous | 3.2 g | Common |
Allen’s | 3.1 g | Common |
Anna’s | 4.9 g | Common |
Ruby-throated | 3.4 g | Occasional |
Calliope | 2.4 g | Rare |
Changing Climate
Climate change is also a factor enabling more hummingbirds to overwinter in northern regions that were historically too cold. Rising temperatures mean more days above freezing and an earlier spring bloom.
Research comparing historical and current hummingbird distribution shows range expansion northward that correlates with warmer average temperatures. For example, Anna’s hummingbirds have moved over 600 miles north in California since the early 1900s.
Milder winters allow flowering plants to bloom earlier and support early-arriving migrants and overwintering individuals. With a changing climate, northern breeders like ruby-throats can survive on a combination of artificial feeders and early flowers.
However, climate change also introduces new challenges like erratic weather. Early warm spells may be followed by deadly cold snaps before birds have migrated. And drought conditions can reduce natural flowers. Supporting overwintering birds with backyard feeders is increasingly important in the face of a changing climate.
Average U.S. Temperature Increase Since 1901
Region | Temperature Increase (°F) |
---|---|
Northeast | 2.4 |
Southeast | 1.5 |
Midwest | 1.5 |
Northern Plains | 2.3 |
Southwest | 2.7 |
Northwest | 1.7 |
Conclusion
While most hummingbirds migrate south to overwinter, some individuals make the remarkable decision to stay behind in their breeding territory. This phenomenon is made possible by a few key factors like food availability, territorial instincts, age, size and a warming climate.
Providing clean feeders with fresh sugar water is the best way to support overwintering hummingbirds. Promoting fall-blooming flowers and protecting habitat are also important to ensure these unique birds can survive the cold months ahead.
The choice certain hummingbirds make to endure rather than migrate speaks to their incredible adaptability and evolutionary drive. Their willingness to overcome severe challenges in order to breed and pass on their genes is inspiring. By supporting overwintering hummingbirds, we can help ensure the future of these captivating creatures.