Kestrels: The Specialized Hovering Hunters of the Falcon Genus
Kestrels are a group of small, predatory birds belonging to the genus Falco. While they share the general characteristics of falcons, kestrels are most easily distinguished by their unique hunting strategy. Unlike many other falcons that hunt actively during flight, kestrels typically hover at heights of 10–20 metres (35–65 ft) over open terrain before swooping down to capture prey, which usually consists of small mammals, lizards, or large insects.
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Key Facts
- Hunting Style: Characterized by hovering over open country before swooping on ground prey.
- Classification: Part of the family Falconidae and genus Falco.
- True Kestrels: Defined by the presence of a malar stripe (a dark vertical mark running down from the eye).
- Evolution: True kestrels likely emerged in Africa during the Late Pliocene or Early Pleistocene.
- Convergent Evolution: The American kestrel resembles true kestrels but is genetically distinct, having evolved similar traits to fill a similar ecological niche.
Evolutionary History and Phylogeny
Research using morphology and mtDNA cytochrome b sequence data suggests that most kestrels form a distinct clade (a group sharing a common ancestor). This group diverged from other members of the Falco genus around the Miocene–Pliocene boundary, approximately 7 to 3.5 million years ago.
The Emergence of True Kestrels
The lineage of "true" kestrels emerged roughly 2.5 to 2 million years ago during the Gelasian age. These birds are characterized by the malar stripe. Originating in Africa, they spread across the Old World, eventually reaching Australia during the Middle Pleistocene, less than one million years ago. This expansion also led to the establishment of several taxa on various Indian Ocean islands.
The Case of the American Kestrel
The American kestrel (Falco sparverius) is the only species in the New World referred to as a kestrel. However, molecular data and morphological traits—such as the black ear-spot and grey wings in males—indicate it is not a true kestrel in a phylogenetic sense. Some evidence suggests it is closer to hobbies, while other DNA analyses link it to larger American falcons like the peregrine, prairie, and aplomado falcons.
This is a prime example of convergent evolution, where the American kestrel evolved to fit a small-prey niche similar to that of true kestrels, despite descending from larger falcon ancestors.
Classification and Groups
Kestrels are categorized into several groups based on their genetic lineage and physical characteristics.
| Group | Notable Species | Primary Distribution |
|---|---|---|
| Malar-striped Clade | Common, Nankeen, Rock, and various Island kestrels | Europe, Asia, Africa, Australia |
| Basal True Kestrels | Greater, Fox, and Lesser kestrels | Africa, Southern Europe, India |
| African Grey Kestrels | Grey, Dickinson's, and Banded kestrels | Central/Southern Africa, Madagascar |
| New World Kestrel | American kestrel | North and South America |
Detailed Species Breakdown
- Malar-striped group: Includes the Common kestrel (Falco tinnunculus), Nankeen kestrel (Australia/New Guinea), and several island species from Mauritius, Seychelles, and Réunion (the latter being extinct since c.1700).
- Basal lineage: Includes the Lesser kestrel, found in India, southern Europe, and most of Africa.
- African grey group: Includes the Banded kestrel of Madagascar and the Grey kestrel of Central to Southern Africa.
Frequently Asked Questions
What makes a kestrel different from other falcons?
The primary difference is their hunting behavior; kestrels hover in place over open ground before diving on prey, whereas other falcons typically hunt through active flight.
What is a malar stripe?
A malar stripe is a dark vertical mark on the face, running down from the eye. It is a defining physical characteristic of the "true" kestrel lineage.
Is the American kestrel a true kestrel?
No. Genetic and morphological evidence suggests the American kestrel is not part of the true kestrel clade but evolved similar characteristics through convergent evolution to hunt similar prey.
Where did kestrels originate?
Evidence suggests that both the early ancestors and the subsequent "true" kestrel lineage evolved in Africa before spreading to other continents.
Which kestrel species is extinct?
The Réunion kestrel (Falco duboisi) is believed to have gone extinct around the year 1700.