The American kestrel (Falco sparverius) is a small falcon found throughout the Americas. It is the only kestrel found in the Western Hemisphere. The American kestrel is known for its ability to hover in place while hunting for prey. It feeds primarily on insects, small mammals, and birds.
The American kestrel belongs to the genus Falco, which includes about 40 species of falcons worldwide. But among this diverse group of raptors, what is the American kestrel’s closest living relative? Determining the evolutionary relationships between organisms helps us better understand their biology and shared history.
Characteristics of the American Kestrel
The American kestrel is a colorful small falcon, with males exhibiting blue-gray wings and a rust-colored back and tail. Females have a similar pattern but with more brown in place of blue-gray. Both sexes have two vertical black stripes on their face, with the male’s stripes thicker and more pronounced.
Some key features of the American kestrel include:
- Small size, about the length of an American robin.
- Long, pointed wings and a slim body adapted for fast flight.
- Two toes pointing forward and two pointing backward on each foot, an arrangement called anisodactyl that allows for strong grasping of prey.
- Large eyes and sharp vision for spotting prey while hovering and soaring.
- Ability to hover in midair by rapidly flapping its wings.
The American kestrel is a cavity nester, using holes in trees, crevices in cliffs, and nest boxes provided by humans. It ranges widely across North and South America, occupying diverse habitats from forests to deserts to urban areas.
Genetic Analysis
Scientists use genetic analysis to determine how closely related different species are and to construct the evolutionary family tree. By sequencing and comparing DNA between organisms, they can estimate how long ago species diverged from common ancestors. The more similar two species’ DNA is, the more recently they shared a common ancestor.
Molecular studies indicate that the American kestrel’s closest living relative is the Eurasian kestrel (Falco tinnunculus). The two species diverged approximately 2 million years ago during the Pleistocene epoch.
The Eurasian kestrel, also called the common kestrel or European kestrel, overlaps in range with the American kestrel across much of Europe and Asia. It is very similar in appearance, size, and habits to its American cousin. The main difference is the Eurasian kestrel lacks the dark back and tail stripes and has more uniform coloration.
Genetic evidence shows the American and Eurasian kestrels share a common ancestor before evolving into separate species in their respective hemispheres. No other falcons show such a close genetic relationship with the American kestrel.
| Species | Genetic similarity with American kestrel |
|---|---|
| Eurasian kestrel | 98.5% |
| Peregrine falcon | 82% |
| Merlin | 81% |
Physical Attributes
In addition to genetic evidence, the American and Eurasian kestrels share many physical features and behaviors indicative of close relationship.
Both species have:
- Compact, slim bodies adapted for aerial agility.
- Long, tapered wings optimal for fast flight.
- Colorful plumage patterns of blue-gray, rufous, and black (though differing in details).
- Ability to swiftly change direction and speed while flying.
- Capacity to beat their wings rapidly to hover in place.
- Habits of hunting small vertebrates and large insects.
- Abilities to reproduce readily in urban and suburban settings.
The two kestrels having such similar morphology and lifestyles supports that they are each other’s closest living relatives. Distantly related falcons like the peregrine have different attributes like larger size, different proportions, and alternative prey preferences.
Behavioral Similarities
American and Eurasian kestrels exhibit parallel behaviors that provide further evidence of their close evolutionary relationship.
Some of their behavioral similarities include:
- Using cavities in trees or man-made structures for nesting.
- Forming monogamous pairs during breeding season.
- Frequently hovering at 30-40 feet high to spot prey in fields.
- Preying on voles, mice, lizards, large insects, and small birds.
- Aggressive territorial defense of nest sites from intruders.
- The ability to thrive in human-altered environments.
The overlaps in American and Eurasian kestrel behavior reflect their near-identical neurological wiring and adaptations for shared lifestyles. More distantly related falcons behave differently, like peregrines that directly pursue prey in flight at great speeds. The common behavioral profile of the two kestrels arises from their close evolutionary kinship.
Habitat Flexibility
American kestrels and Eurasian kestrels both exhibit great flexibility in using diverse habitats, which facilitates their wide distribution.
The American kestrel occupies habitats including:
- Grasslands
- Meadows
- Agricultural fields
- Deserts
- Scrublands
- Woodland edges
- Urban areas
The Eurasian kestrel inhabits:
- Grasslands
- Farmlands
- Heathlands
- Moorlands
- Cliffs
- Urban areas
- Tundra
Their shared ability to thrive in diverse habitats has allowed both species to achieve extensive ranges across their hemispheres as generalist predators. More specialized falcons have more restricted distributions. The flexible habitat use of the kestrels reflects their evolution as small, opportunistic hunters.
Diet Flexibility
The American and Eurasian kestrels also exhibit a high degree of flexibility in their diets, another indicator of their close relationship.
American kestrels consume a wide variety of prey including:
- Insects
- Rodents
- Small birds
- Reptiles
- Amphibians
Similarly, Eurasian kestrels eat:
- Voles
- Mice
- Moles
- Lizards
- Large insects
Their ability to thrive on diverse prey types has allowed both kestrels to succeed across many environments and conditions. More specialized falcons like the peregrine rely on a narrower diet dominated by birds. The generalist feeding behaviors of the American and Eurasian kestrels reflect their evolution as opportunistic predators able to exploit a wide range of prey.
Evolutionary History
The American and Eurasian kestrels share an evolutionary lineage tracing back to a common ancestor species in the ancient genus Falco.
Approximately 6 million years ago during the late Miocene, the ancestral Falco lineage diverged from other falcon groups. For several million years, these primitive kestrel-like falcons spread across Europe, Asia, and North America.
Then around 2 million years ago in the early Pleistocene, populations became isolated between the Old World and New World. This separation led to the divergence into distinct European and North American species – the direct ancestors of today’s Eurasian and American kestrels respectively.
The ancient Falco kestrels likely inhabited open habitats and preyed on small vertebrates and insects much as modern kestrels do. Over time, the American and Eurasian kestrels evolved minor variations in size, plumage, and habitat preference – but retained their core adaptations for hunting agile, aerial prey.
This shared pedigree explains the modern kestrels’ extreme closeness as well as subtle differences. Their common descent accounts for their genetic, physical, behavioral, and ecological similarities. No other living falcon lineages are so closely allied.
Conclusion
In conclusion, extensive genetic, morphological, behavioral, and evolutionary evidence conclusively demonstrates that the Eurasian kestrel is the closest living relative to the American kestrel.
Molecular studies show nearly 99% genetic similarity between the two species, indicating they diverged from a common ancestor only around 2 million years ago. The kestrels’ similar body plans, plumage patterns, hunting techniques, nesting habits, habitat flexibility, and diets all reflect their close relationship.
No other falcons display such a high degree of kinship with the American kestrel across so many attributes. More distantly related falcons like the peregrine and merlin exhibit greater differences. The similarities between the American kestrel and Eurasian kestrel arise from their relatively recent divergence from a shared lineage specialized for hunting agile, small prey.
Determining the closest evolutionary relatives of organisms provides insight into their biology and ecology. The remarkable degree of closeness between the American and Eurasian kestrels will help guide future research into these widespread, iconic raptors. Their ability to thrive from tundra to tropics speaks to their success as versatile, highly evolvable predators.
