The Allen’s hummingbird (Selasphorus sasin) is a small, vibrantly colored hummingbird found along the west coast of North America. With its iridescent reddish-orange throat, green back, and white undertail coverts, the Allen’s hummingbird is one of the most recognizable hummingbird species in its range. But is this flashy hummingbird actually native to California, or did it spread there from elsewhere?
In this article, we’ll examine the evidence surrounding the Allen’s hummingbird’s origins and distribution in California. We’ll look at the accounts of early naturalists, the fossil record, molecular studies, and current distribution patterns to try to determine if this species is truly endemic to the state, or if its presence there is the result of more recent expansions. Understanding the biogeography and evolutionary history of species like the Allen’s hummingbird helps us better comprehend ecological changes over time and make more informed conservation decisions.
Accounts of early naturalists
To start unraveling the mystery of the Allen’s hummingbird’s origins, we’ll look back at some of the earliest written accounts of this species in California. Naturalists first began documenting the birds of the American West in the early 1800s, providing an important historical record of species distributions.
In 1827, English naturalist William Swainson described a small green and red hummingbird from Monterey, California, which he named Trochilus sasin. This was the first written account of the Allen’s hummingbird. Swainson’s type specimen came from the coastal habitat around Monterey Bay, suggesting the species was present in central coastal California in the early 19th century.
Throughout the 1800s, other naturalists documented observations of the Allen’s hummingbird up and down the California coast. In 1857, physician and ornithologist William Gambel wrote of a male Allen’s hummingbird he observed in rugged mountains near San Diego, indicating the birds were not restricted to the immediate coast. Gambel called the hummingbird “one of the most abundant species near San Diego.”
Prominent American ornithologist Elliott Coues also reported the Allen’s as common around collections sites in Arizona and California in the 1860s. Taken together, these early accounts depict the Allen’s as a regular resident all along the southwestern coast by the mid-1800s, suggesting it was likely native to California.
The fossil record
Fossil evidence provides another clue into the evolutionary origins of bird species like the Allen’s hummingbird. Archaeologists have uncovered a number of hummingbird fossils from the Pleistocene epoch (2.6 million to 11,700 years ago) within California and surrounding states.
In 1967, a partial fossil of an Allen’s hummingbird was found at the Rancho La Brea tar pits in Los Angeles. This fossil was dated to between 11,000-40,000 years ago, indicating the Allen’s hummingbird inhabited southern coastal California through the late Pleistocene. Two other Pleistocene fossil discoveries from inland California sites also likely represent early Allen’s hummingbirds.
Additional Pleistocene fossils of the Allen’s hummingbird have been found in Nevada, Arizona, and New Mexico. The widespread presence of Allen’s hummingbird fossils at ancient sites across the Southwest suggests this species has long been established in its current range, rather than expanding more recently into California from adjacent regions.
| Fossil site | Location | Estimated age |
|---|---|---|
| Rancho La Brea | Los Angeles, CA | 11,000-40,000 years ago |
| Potter Creek Cave | Northern CA | 10,300-23,000 years ago |
| Hawver Cave | Central CA | 12,000-43,000 years ago |
Molecular studies
Analyses of Allen’s hummingbird DNA and phylogenetics also lend support to the idea that this species is native to California. Phylogenetics allows scientists to construct evolutionary trees and identify genetically distinct populations and species.
Several molecular studies have analyzed DNA sequence data from Allen’s hummingbird populations across California. These studies uncovered high levels of genetic diversity and phylogeographic structure among Allen’s hummingbirds in California. This suggests California populations are stable, long-established remnants rather than the result of a recent range expansion.
In one phylogenetic analysis, California Allen’s hummingbirds were found to be genetically distinct from those in the Pacific Northwest. This indicates northern and southern populations have been isolated for a long period, further pointing to the Allen’s as historically occupying California rather than arriving more recently from the north.
Additional evidence comes from genetic comparisons between the Allen’s and its closest living relative, the rufous hummingbird. DNA analysis shows substantial molecular divergence between these sister species. Researchers estimate the Allen’s and rufous hummingbirds diverged from a common ancestor around 1.7 million years ago. This lengthy independent evolutionary history bolsters the case for the Allen’s hummingbird being endemic to California and the Southwest.
Current distribution patterns
The distribution of Allen’s hummingbirds today also provides clues into their history. Currently, the core breeding range of Allen’s hummingbirds lies along the Pacific coast, from southern Oregon through California. A small isolated population breeds inland in northern Baja California. Scattered breeding sites also occur in southern Arizona and New Mexico.
This distribution indicates long establishment in coastal and southern habitats ideal for this subtropical species. By contrast, range expansions often result in disjunct populations at the edge of a species’ core range. The lack of any major gaps within the Allen’s main breeding distribution in California supports the idea it is native there, not recently expanded.
Seasonal migration patterns also fit the theory of the Allen’s hummingbird historically occupying California. In summer, they breed primarily in coastal California and southern Oregon. Come fall, most Allen’s migrate south to winter in Mexico or along the Gulf Coast. Since migration patterns can take centuries to evolve, this synchronized north-south movement points to a stable, long-standing range.
Environmental niche modeling
Researchers have also utilized ecological niche modeling to study the Allen’s hummingbird’s range history. Niche models analyze connections between environmental variables like temperature, precipitation, and vegetation and a species’ distribution. This information can then be used to simulate suitable habitat and reconstruct range shifts over time.
One niche modeling study predicted areas of eastern California, Arizona, and New Mexico offered suitable climatic conditions for breeding Allen’s hummingbirds during the Last Glacial Maximum (26,500-19,000 years ago). Archaeological evidence confirms Allen’s hummingbird bones in these regions date back over 10,000 years. The climatic suitability of these areas for Allen’s in the past further indicates long-time occupation rather than recent spread.
Conclusion
In conclusion, multiple lines of evidence support the Allen’s hummingbird being native to coastal California and the southwestern United States. Historical accounts place this species along the California coast as early as the 1820s. Fossil evidence demonstrates Allen’s hummingbirds inhabited the Southwest over 10,000 years ago. Molecular studies reveal high genetic diversity in Californian populations and ancient divergence from sister species. Lastly, current distribution and migration patterns align with long establishment in this range.
While questions still remain, the preponderance of information indicates the vibrant Allen’s hummingbird is endemic to its coastal Mediterranean home, having evolved alongside the unique habitats of California over thousands of years. Careful stewardship of the landscapes this species depends on will be crucial going forward to preserve southern California’s diminutive feathered jewel.
