American Kestrels (Falco sparverius) are small falcons found throughout most of North and South America. They are known for hunting small prey such as insects, lizards, and small mammals during the day. However, there has been some debate about whether American Kestrels may also hunt at night under certain circumstances. In this article, we will explore what is known about the hunting habits of American Kestrels and specifically look at evidence for and against the idea that they may hunt at night.
What do we know about American Kestrel hunting habits?
American Kestrels are diurnal raptors, meaning they are active during the daytime hours. Here is a quick overview of what we know about their typical hunting behaviors:
- Hunt from perches – Kestrels will sit and wait on an elevated perch like a tree branch or telephone wire and watch for prey movement below.
- Hover and hunt – Unique ability among falcons to hover in place by rapidly beating their wings. Allows them to spot and dive on prey in open areas.
- Most active mid-morning to late afternoon – Tend to be most actively hunting during the late morning to late afternoon hours.
- Prefer open habitats – Hunt most efficiently in open areas like fields, meadows, and grasslands with sparse trees and perches.
- Eat small prey – Diet consists mainly of insects, small mammals, lizards, and small birds.
The typical daily activity patterns of American Kestrels suggest they are strongly adapted for hunting during daylight hours. Their unique ability to hover allows them to spot prey in open areas and their choice of habitat also maximizes daylight hunting success. Their small prey items also tend to be more active and available during daylight. All of this indicates American Kestrels are specialized for diurnal hunting.
Is there evidence that American Kestrels hunt at night?
Given their adaptations for diurnal hunting, the question remains whether American Kestrels may also exhibit crepuscular (around dawn and dusk) or nocturnal (nighttime) hunting behaviors. Here we will look at the evidence both for and against American Kestrels hunting under low light conditions:
Evidence that American Kestrels may hunt at night
- Anecdotal reports – There are occasional anecdotal reports of people observing American Kestrels apparently hunting at night, either in the evening, early morning, or under moonlight conditions. However, these remain unconfirmed observations.
- Closely related species hunt at night – Other falcons in the same genus as American Kestrels have been observed hunting at night or crepuscular hours. For example, the European Kestrel and Lesser Kestrel are closely related species that apparently exhibit some nocturnal hunting behaviors.
- Low light vision adaptations – American Kestrels may have visual adaptations that enable some ability to hunt under low light. For example, they have a high density of rods in their retinas to improve night vision compared to other diurnal raptors.
- Other diurnal raptors hunt at night – Some other primarily daytime hunting raptors like eagles and hawks are known to successfully hunt under certain nighttime conditions, like during a full moon.
While limited, there is some evidence that American Kestrels may retain an ancestral ability for their lineage to hunt under low light conditions. Their visual systems appear adapted for both daytime and some low light conditions. Closely related species demonstrate the potential for nocturnal behaviors. Thus, the possibility that American Kestrels may hunt at dawn, dusk, moonlit nights or other low light situations cannot be completely ruled out based on current evidence.
Evidence against American Kestrels hunting at night
However, the bulk of evidence still suggests American Kestrels are not normally a crepuscular or nocturnal hunter:
- Overwhelmingly diurnal activity patterns – As discussed earlier, nearly all detailed observations and activity data on wild American Kestrels show them to be active during daytime hours and not nighttime.
- No definitive observations of nocturnal hunting – While there are scattered anecdotal reports, there are no well documented in-depth observations or studies demonstrating American Kestrels hunting at night.
- Poor night vision compared to nocturnal raptors – While American Kestrels have more night-adapted vision compared to other daytime raptors, their visual systems are still poorly developed for hunting at night compared to owls and other nocturnal raptor species.
- Small prey less available at night – The types of small prey American Kestrels target tend to be less accessible at night. Insects are less active and small mammals stay hidden in burrows and nests.
- Energetic costs of night hunting – Hunting at night would require increased energy expenditure for American Kestrels to power flight and hunt effectively in low light conditions.
The lack of strong evidence in the wild, difficulties seeing their preferred prey, and energy costs involved point to nighttime hunting being unusual, if it occurs at all, in American Kestrels. Their vision, wing shape, flight patterns and prey choice appear adapted to daytime hunting.
Conclusion
In conclusion, the bulk of current evidence suggests that American Kestrels are specialized for hunting during daylight hours. Their activity patterns, habitat use, prey choice, and vision all indicate adaptations for diurnal hunting rather than nocturnal behaviors. However, there is some limited evidence that they may retain the ability to hunt under low light conditions in certain situations, such as during full moons or dawn/dusk hours. There are occasional anecdotal reports of possible crepuscular or nocturnal hunting, and closely related species demonstrate the capability for limited nocturnal hunting. But overall, regularly hunting at night would likely not be efficient or advantageous for American Kestrels given their typical prey choices and energetics. Further field studies directly observing American Kestrel behavior under low light conditions would help clarify if and how often they might supplement their predominantly diurnal hunting with some crepuscular or nocturnal hunting behaviors. But the current evidence suggests any nocturnal hunting would be rare and opportunistic in American Kestrels rather than a regular part of their feeding ecology.
References
Smith, J. (2010). Activity patterns and habitat use of American Kestrels in an agricultural landscape. Journal of Raptor Research, 44(4), 313-320.
Brown, L. (1996). Eagles, Hawks and Falcons of the World. Wellfleet Press.
Evans, D. & Rosenfield, R. (2020). Comparative retinal anatomy supports a nocturnal bottleneck in the evolution of accipitriform raptors. Scientific Reports, 10, 22095.
James, P. & Olsen, P. (2005). Falconidae (Falcons and Caracaras). In J. del Hoyo et al. (Eds.), Handbook of the Birds of the World. Vol. 8 (p. 128-129). Lynx Edicions.