Bird of prey

Birds of prey are a diverse group of hypercarnivorous avian species that actively hunt and feed on other vertebrates, including mammals, reptiles, and smaller birds. Characterised by powerful flight, exceptional eyesight, and specialised anatomical adaptations, they occupy key ecological niches as apex or meso-predators. Despite their common association under the term “raptor”, the grouping is paraphyletic, reflecting convergent evolution rather than a single unified lineage. Modern scientific usage restricts birds of prey to two principal diurnal orders—Accipitriformes and Falconiformes—and one nocturnal order, Strigiformes, although additional taxa are sometimes considered within this broad category.

Morphology and Hunting Adaptations

Birds of prey display several distinctive features that enable efficient predation. Most species possess highly developed binocular vision capable of detecting prey at long distances, often several times sharper than that of humans. Their feet typically bear strong, sharply curved talons, used either for piercing or grasping prey, while the beaks are robust and hooked for tearing flesh.
Notable adaptations include:

• Enhanced flight capabilities, ranging from the high-speed stoops of falcons to the broad-winged soaring of eagles and vultures.
• Variable leg and toe morphology, aligned with ecological roles; for instance, ospreys have reversible outer toes for grasping fish.
• Silent flight mechanisms in owls, facilitated by specialised feather edges that reduce turbulence.

These physiological traits underpin their efficiency as predators and, in some cases, scavengers.

Diversity and Common Groupings

Although “raptor” is widely used as a general term, the classification of birds of prey is historically inconsistent. Many English names originated in Britain and were later applied to similar birds in other regions.

Accipitriformes

This order includes hawks, eagles, buzzards, kites, harriers, the osprey, and Old World vultures. Typical features include powerful builds, broad wings, and keen eyesight. Major groupings include:

• Eagles (Aquilinae) – Typically large raptors with feathered legs and heavy talons; they build substantial stick nests.
• Hawks (Accipiter species) – Medium-sized woodland hunters that launch rapid attacks from concealed perches; known for long tails and agile flight.
• Buzzards (Buteo species) – Broad-winged raptors that soar extensively; in North America often called hawks.
• Harriers (Circus species) – Slender birds with long legs and tails; distinguished by a characteristic low gliding flight over open landscapes.
• Old World vultures – Specialised scavengers with featherless heads and large wingspans designed for soaring.

Falconiformes

Falcons and caracaras belong to this order. Unlike accipitrids, falcons kill with the beak rather than the feet.

• Falcons and kestrels – Swift, agile fliers with tapered wings; the peregrine falcon is noted for its exceptional diving speed.
• Caracaras – Primarily Neotropical generalists with broad wings and often bare faces; more opportunistic than most other falconids.

Strigiformes

The owls represent the nocturnal birds of prey. These include:

• Typical owls (Strigidae) – Diverse in size and habitat, characterised by forward-facing eyes and acute hearing.
• Barn and bay owls (Tytonidae) – Recognised by heart-shaped facial discs that enhance sound localisation.

Additional Raptor-like Birds

• The secretary bird – A large, long-legged terrestrial raptor of African grasslands; hunts primarily on foot.
• The osprey – A unique fish-eating specialist found worldwide, often considered in its own family due to distinct adaptations.

Historical Classification

Early taxonomic systems, such as those devised by Carl Linnaeus, grouped all predatory birds into the order Accipitres, subdividing them by a mixture of anatomical and behavioural criteria. Linnaeus’s broad categories included vultures, falcons, owls, and even shrikes, reflecting limited understanding of avian evolutionary relationships.
Subsequent authors expanded and refined these schemes. Louis Pierre Vieillot was influential in distinguishing diurnal and nocturnal raptors, proposing multiple families and adopting several additional genera. His work separated shrikes from true birds of prey, a distinction supported by later research.
Throughout the nineteenth and twentieth centuries, taxonomists frequently rearranged raptor classifications, sometimes placing owls and falcons together under the now-deprecated superorder Falconimorphae. Many of these placements were based solely on morphological similarities, some of which were the result of convergent evolution.

Modern Systematics

Advances in molecular biology have significantly re-shaped understanding of raptor evolution. Accipitriformes are now recognised as having diverged approximately 44 million years ago from a common ancestor with the secretary bird. Multiple phylogenetic studies have revealed extensive paraphyly within traditional groupings, particularly among accipitrids, where similarities in form often obscure deeper evolutionary divides.
Key features of modern systematics include:

• Accipitriformes and Falconiformes are not sister groups; falcons are more closely related to parrots and passerines.
• Owls (Strigiformes) belong to Afroavian radiations, separate from diurnal raptors.
• New World vultures (Cathartidae) have been variably placed within Accipitriformes, in their own order (Cathartiformes), or formerly within Ciconiiformes due to earlier misconceptions regarding their relationships to storks.
• Phylogenomic studies continue to refine these relationships, with some proposing new clades such as Hieraves, uniting Strigiformes and Accipitriformes.

Ecology and Behaviour

Birds of prey occupy a wide range of habitats, from arid deserts to dense forests and coastal regions. Their ecological roles vary significantly:

• Apex predators, such as golden eagles, regulate prey populations and maintain ecological balance.
• Scavengers, including condors and vultures, provide essential ecosystem services through carrion removal.
• Specialists, such as harriers and kestrels, exploit narrow ecological niches, from small mammal predation to insect hunting.

Feeding behaviour ranges from high-speed aerial hunting to patient soaring and ambush strategies. Prey selection is influenced by body size, habitat, and hunting technique.

Evolutionary Considerations and Extinct Forms

Fossil evidence indicates that several extinct bird lineages displayed raptor-like adaptations. Certain telluravian birds, including members of Sandcoleidae and Messelasturidae, possessed talons similar to those of modern birds of prey, suggesting either ancient shared ancestry or convergent evolution.
Cariamiformes, which include modern seriemas and the extinct terror birds, have been proposed by some researchers as potential additions to the broader raptor grouping. These birds were effective vertebrate predators, though they were not traditionally considered birds of prey in the classical sense.

Contemporary Scientific Discussions

Modern ornithology continues to debate the boundaries of what constitutes a bird of prey. Strict definitions emphasise active predation using specialised talons and beaks, while broader interpretations may include scavengers, piscivores, and certain opportunistic predators. Phylogenetic research, particularly whole-genome analyses, continues to reveal unexpected relationships, challenging long-held assumptions and prompting revisions to avian classification.
Birds of prey remain a focal point of ecological and evolutionary research due to their global distribution, diverse morphologies, and critical roles within ecosystems. Their continued study provides insight into avian evolution, environmental health, and conservation science.