The ruby-throated hummingbird (Archilochus colubris) is one of the most common hummingbird species in North America. These tiny, energetic birds are best known for their iridescent plumage and their ability to hover in midair as they sip nectar from flowers. Understanding the typical lifespan and mortality rates of ruby-throated hummingbirds can provide insight into their population dynamics and conservation needs.
Typical Lifespan
The average lifespan of a wild ruby-throated hummingbird is 3-5 years. However, they have been known to live up to 9 years in the wild. Lifespans are estimated based on recapture studies of banded ruby-throats. The most extensive study, conducted between 1987-1996, found the average lifespan of banded adult males was 3.4 years and banded females was 3.9 years.
In captivity, with ideal care, food, and lack of predators, ruby-throats may live even longer. The longevity record for a captive male ruby-throat is 12 years, 11 months. However, average captive lifespan ranges between 5-8 years.
Mortality Rates Throughout Life
Mortality rates are highest in the first year of life across all hummingbird species. Estimates suggest that only 20-50% of ruby-throats survive to their first breeding season. The survivorship tends to increase once the young birds reach adulthood, but then gradually declines again as the birds age.
High first-year mortality is attributed to the challenges fledglings face learning to forage on their own after leaving the nest. Natural predators, lack of food sources, and cold temperatures in their northern breeding grounds also contribute to juvenile deaths. Adult hummingbirds face threats from predators, disease, weather events, habitat loss, and natural causes.
One 20-year study of ruby-throats in Wisconsin analyzed survivorship and mortality rates across different age classes:
| Age Class | Annual Survivorship | Annual Mortality Rate |
|---|---|---|
| Juveniles (0-1 years) | 0.2 | 0.8 |
| Yearlings (1-2 years) | 0.45 | 0.55 |
| Adults (2+ years) | 0.6 | 0.4 |
As shown, only about 20% of hatchlings survived to their first birthday. Mortality rates declined but remained high for yearlings. Survivorship was highest for adults. These trends are typical for ruby-throats and many other small bird species.
Causes of Mortality
The specific causes of mortality for wild ruby-throated hummingbirds are challenging to study and document. However, researchers have identified some key factors that contribute to deaths within this species:
Predators
Young, inexperienced hummingbirds are vulnerable to predators, especially during the post-fledging period when they leave the nest. Domestic cats pose a significant threat, killing millions of hummingbirds in the U.S. and Canada each year. Snakes, frogs, lizards, and praying mantises may prey on nestlings. Hawks, falcons, and other raptors hunt adult hummingbirds.
Starvation
Access to adequate food resources is critical, as hummingbirds have among the highest metabolic rates of any vertebrate. Fledglings learning to forage and migrants that encounter poor flowering conditions along their migration routes face higher risks of starvation. Harsh weather, insect infestations, and habitat loss can limit the availability of nectar sources.
Extreme Weather
Cold temperatures, storms, and other severe weather events can lead to direct mortality through exposure or loss of essential food sources. Migrating ruby-throats are especially susceptible when facing unfavorable winds or weather at ecological barriers like the Gulf of Mexico.
Disease
Bacterial, viral, fungal, and parasitic infections have all been documented in wild ruby-throats. Examples include salmonellosis, West Nile virus, Aspergillus fungi, and intestinal protozoa. Sick birds often appear lethargic and unwell before rapidly dying.
Habitat Loss
Declines in natural food sources due to urbanization, agricultural practices, and climate change pressures can leave hummingbirds without enough sustenance. Habitat degradation contributes to long-term population declines.
Collisions
Hummingbirds are prone to fly into manmade objects including windows, cars, fences, wind turbines, and power lines. Such collisions may cause direct mortality or injure the birds in ways that eventually lead to death.
Natural Causes
Given their high metabolic rate, diseases and organ failures tied to aging likely claim many older ruby-throats. Predation and accidents also cull sick or slowing birds from the population.
Impacts on Population
The ruby-throated hummingbird has a large breeding range and total population estimated at around 7 million birds. Overall the species is still common and widespread, leading the IUCN Red List to classify it as a species of Least Concern. However, some local populations have experienced declines likely linked to habitat changes and pesticide use reducing food availability.
The high first-year mortality places pressure on females to produce enough offspring to maintain population levels. Each female lays 1-3 tiny eggs per brood and may raise 2-3 broods per season. Despite their small size, these energetic hummingbirds play an important role as pollinators for wildflowers, shrubs, and trees.
Researchers recommend further studies to track mortality causes and rates across the full annual cycle of ruby-throats. Such data can inform conservation strategies to support their populations into the future.
Conclusion
In summary, ruby-throated hummingbirds typically live 3-5 years in the wild, with lifespans reaching up to 9 years documented. Mortality rates are highest in the first year, then gradually increase again as birds age and natural causes take their toll. A variety of factors contribute to deaths, especially predators, starvation, weather events, disease, habitat loss, and collisions.
Understanding the patterns of survivorship and mortality provides insights into population dynamics for this charismatic pollinator. Supporting hummingbird conservation helps ensure future generations can continue to enjoy these captivating birds. With care and habitat protections, ruby-throats will continue gracing backyards and gardens with their energetic antics and flashes of vibrant color.
