Birds of prey, also known as raptors, include hawks, falcons, owls, eagles, and vultures. These predators have excellent eyesight and powerful talons that allow them to hunt small animals such as rodents, reptiles, and other birds. But when it comes to hunting at night, not all raptors are equal.
The Vision of Raptors
To understand raptor vision, we first need to distinguish between diurnal and nocturnal birds of prey. Diurnal raptors like hawks, falcons, and eagles are active during the daytime. They have excellent long-distance vision to spot prey while flying high above the ground. Their eyes are placed more towards the front of their heads, like human eyes, giving them overlapping fields of view for depth perception. The retina of diurnal raptors contains a high concentration of cone photoreceptor cells that are sensitive to color vision.
In contrast, nocturnal raptors like owls are active at night. They have evolved different visual adaptations to function in low-light conditions. Owls have large, forward-facing eyes that maximize light intake. Their retinas contain abundant rod photoreceptors, which are more sensitive to light and motion. Owls see well enough in dim light to hunt, but their vision is greyscale rather than color.
So while owls are equipped for nocturnal hunting, most hawks, falcons and eagles do not have the visual acuity to effectively hunt prey at night. Their daytime vision gives them an advantage during daylight hours.
Hunting Strategies of Raptors
In addition to differences in vision, raptors have adopted various hunting strategies based on when they are active. Here’s an overview of how some common types of raptors hunt:
Falcons
Falcons like the peregrine falcon and American kestrel are nimble, fast fliers that pursue prey while flying. Using their incredible speed and maneuverability, they overwhelm prey mid-air with surprise attacks. Falcon species that are active during the day rely heavily on sight for targeting prey and guiding their aerial pursuits. For that reason, most falcons do not hunt at night.
Accipiters
Accipiters such as sharp-shinned hawks and Cooper’s hawks have short, rounded wings and long tails that allow them to deftly maneuver through dense vegetation in pursuit of prey. Using the cover of trees and shrubs, they surprise small birds and mammals with quick chases and captures. Limited by their daylight vision, most accipiters are not adept at hunting in complete darkness.
Buteos
Soaring hawks like red-tailed hawks and ferruginous hawks have broad wings suited for longer gliding flight. From an aerial vantage point, they scan the ground for prey such as rodents and snakes. With their keen daytime vision, they can spot prey from hundreds of feet in the air before dropping down to attack. Low light conditions at night reduce their ability to find prey while flying.
Eagles
Bald eagles and golden eagles are opportunistic hunters that sometimes hunt from the air but also steal prey from other birds. They frequently hunt near water, where they snatch fish from the surface. Eagles that hunt during the day rely heavily on eyesight to find prey. Those that live in northern climates may adapt to hunting at dawn and dusk in winter when days are shorter.
Owls
Owls like the great horned owl and barred owl have adapted to be effective nocturnal hunters. Their light-sensitive eyes and silent flight feathers allow them to locate and capture prey under cover of darkness. Some owls rely on their acute hearing to locate prey in vegetation by the sounds of movement. Unlike most diurnal raptors, the majority of owl species worldwide are well equipped for hunting at night.
Nocturnal Behavior in Diurnal Raptors
While the majority of diurnal raptors do not hunt at night, they may still be active around dusk and dawn. Crepuscular activity allows them to take advantage of low light conditions while still benefiting from their daylight vision. Some examples include:
- Northern harriers that feed on rodents may hunt at dawn and dusk when small mammals are most active.
- Red-tailed hawks begin flying from their night roosts before sunrise to stake out hunting perches at first light.
- American kestrels that nest in cavities often enter and exit the nest cavity at dusk and dawn.
A few diurnal raptors have been observed sporadically hunting at night, including:
- Peregrine falcons may opportunistically hunt nocturnal species like bats and owls that become active at night.
- SomeAccipiters like Cooper’s hawks may hunt at night around artificial lights that attract concentrations of birds.
- Bald eagles will scavenge at night and may even hunt vulnerable prey like resting waterfowl under the right conditions.
But most biologists agree that the majority of hawks, eagles, and falcons do not have sufficient vision adapted for successful nighttime hunting. While they may sometimes take advantage of unique nocturnal opportunities, daytime remains their peak hunting time when their senses are best adapted for finding and capturing prey.
Do Any Raptors Only Hunt at Night?
Most raptor species hunt both day and night or specialize in either diurnal or nocturnal hunting. But there are a few rare exceptions of raptors that seem to only hunt at night:
- The rare black-and-white owl (Strix nigrolineata) of South America appears to be mostly nocturnal, but very little is known about this mysterious species.
- The Papuan hawk-owl (Uroglaux dimorpha) of New Guinea is reported to be strictly nocturnal, unlike most other hawk-owl species that hunt in twilight.
- The spot-tailed nightjar (Hydropsalis maculicaudus) of Central and South America belongs to the nightjar family, related to owls and frogmouths, and exclusively hunts insects at night.
But apart from these exceptional species that have evolved for dedicated nocturnality, most birds of prey are flexible in their activity patterns. The differences between daytime and nighttime hunters underscore how diverse raptors have specialized their senses and strategies to take advantage of the opportunities afforded by both day and night.
Conclusion
In summary, most hawks, eagles, and falcons have vision adapted for diurnal hunting and do not typically hunt at night. Owls have evolved for nocturnal hunting with their specialized eyesight, hearing, and silent flight. Some diurnal raptors show limited crepuscular or nocturnal activity, but night hunting is challenging without the visual acuity they possess during daylight hours. Raptors demonstrate a wide range of sensory and behavioral adaptations that allow different species to hunt successfully both day and night.