Hummingbirds have an incredible strategy to survive food shortages
Hummingbirds may be among the smallest birds in the world, but they endure some of the most grueling migrations. Some species travel more than 9,000 km (5,590 miles) annually, relying almost entirely on nectar from wildflowers to fuel their journeys.
This nectar is quickly converted into fat, which serves as their primary energy reserve. However, climate change and habitat loss are making the distribution of wildflowers along the birds’ migratory routes increasingly unpredictable.
To cope with these challenges, hummingbirds rely on a remarkable physiological adaptation called torpor, a temporary hibernation-like state that allows them to conserve energy.
Understanding how and when hummingbirds use torpor is crucial for conservation efforts, especially as environmental changes continue to threaten their survival.
Hummingbird migration and food availability
A recent study led by Shayne R. Halter, a Ph.D. candidate at The University of New Mexico (UNM), provides new insights into how hummingbirds regulate their energy reserves during migration.
The research was conducted in collaboration with UNM Professor Blair Wolf and University of Wyoming Professor Emeritus Carlos Martinez del Rio.
Halter’s research focused on Rufous (Selasphorus rufus) and Calliope (Selasphorus calliope) hummingbirds migrating through New Mexico in the fall.
The goal was to determine the role of fat reserves in regulating torpor usage and how these tiny birds adjust their metabolism in response to uncertain food availability.
Conserving energy to survive
Torpor is a survival mechanism that allows hummingbirds to dramatically lower their metabolic rate and body temperature for several hours, typically overnight. Unlike hibernation, which lasts for days or months, torpor is temporary and allows the birds to conserve energy when food sources are scarce.
“During torpor, hummingbirds are unaware of their surroundings, making them more vulnerable to predation and other risks. For this reason, torpor should only be used when needed,” Shayne Halter explains.
Hummingbirds enter torpor when their body fat reserves are too low to sustain their high-energy needs through the night. Without it, they risk starving before sunrise, when they can begin feeding again.
Halter’s research identified a critical fat threshold that determines when a hummingbird will enter torpor. His findings show that hummingbirds initiate torpor when their fat levels drop below 500 milligrams at night and ensure they wake up with at least 180 milligrams of fat in the morning to sustain them until they find food.
If a bird has enough fat, it will avoid torpor, since staying alert reduces the risk of predation. If food is scarce and fat reserves are low, the bird will enter torpor and adjust its duration to preserve a minimal morning fat reserve.
Climate change and habitat loss
Hummingbirds are facing increasing challenges due to climate change and habitat destruction. The southwestern United States, a critical migratory corridor, is experiencing rising temperatures, prolonged droughts, and unpredictable nectar availability.
Land-use changes, such as urban development and the spread of invasive, non-nectar-producing plants, are further reducing food sources along their migration routes.
“Annual migrations are demanding events for hummingbirds and are often accompanied by high mortality rates. The arid southwest is becoming warmer and drier, and these conditions are already affecting the timing and distribution of nectar sources,” noted Halter.
These environmental shifts may force hummingbirds to rely more on torpor, potentially altering their migration success rates and survival. If nectar becomes too scarce, more birds may struggle to maintain the fat reserves they need to sustain their journeys.
As their environment becomes increasingly unpredictable, their ability to adapt will be tested like never before.
Monitoring the health of hummingbirds
Halter’s study not only advances our understanding of hummingbird physiology but also provides a predictive model for conservation efforts.
By analyzing torpor frequencies, durations, and fat reserves, scientists can assess the ecological health of hummingbird populations and monitor how they are adapting to environmental changes.
A better understanding of how hummingbirds regulate energy during migration can help guide conservation strategies.
Protecting and restoring native wildflower habitats along migratory routes will be crucial for ensuring that hummingbirds have consistent food sources. Identifying key stopover sites where hummingbirds refuel and ensuring these locations remain rich in nectar-producing plants could further support their survival.
Researchers can also use Halter’s predictive model to determine how climate change might affect hummingbird migration patterns and energy balance in the future.
By providing critical data on how much energy hummingbirds need to survive and how they adapt to changing conditions, this research offers valuable insights for conservationists working to protect these tiny but resilient birds.
Future of migrating hummingbirds
Hummingbirds are an incredible example of nature’s adaptability. Despite their small size, they undertake some of the most demanding migrations in the animal kingdom. Hummingbirds ability to strategically use torpor to survive periods of low food availability is a testament to their resilience.
However, as climate change and habitat loss continue to threaten their food supply, these birds may be forced to adapt in ways that could impact their long-term survival.
By understanding their energy needs and the role of torpor in their survival, we can take meaningful steps to protect these remarkable birds for generations to come.
The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.
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