Burrowing owls and ground squirrels are two common wildlife species that share overlapping habitats across North America. As both are small prey animals that live underground, an obvious question arises – do burrowing owls eat ground squirrels? The short answer is yes, burrowing owls are opportunistic predators that will eat ground squirrels if given the chance. However, the full relationship between these two species is more complex.
Burrowing Owl Overview
The burrowing owl (Athene cunicularia) is a small, long-legged owl found in open, treeless grasslands across North and South America. As their name suggests, they nest and roost in burrows in the ground, often those dug out and abandoned by ground squirrels or prairie dogs.
Burrowing owls are partly migratory – northern populations migrate south for the winter, while southern birds are often year-round residents. They have distinct white eyebrow markings and bright yellow eyes. An adult burrowing owl reaches about 9-11 inches in height and weighs 4-9 oz.
Ground Squirrel Overview
Ground squirrels are a group of small squirrel species that live in underground burrow systems. There are over 20 species found across North America, with some of the most common including:
- California ground squirrel
- Columbian ground squirrel
- Franklin’s ground squirrel
- Thirteen-lined ground squirrel
- Golden-mantled ground squirrel
Ground squirrels are active during the day. They spend time above ground foraging, but retreat to their burrows to avoid predators and sleep. Ground squirrels are omnivorous; their diet consists of seeds, nuts, roots, grains, berries, leaves, fungi and sometimes insects or eggs.
Do Burrowing Owls Prey on Ground Squirrels?
The simple answer is yes, burrowing owls do prey upon and eat ground squirrels. However, ground squirrels make up a relatively small part of the owl’s overall diet.
Evidence That Burrowing Owls Eat Ground Squirrels
There are several lines of evidence indicating that burrowing owls directly prey upon ground squirrels:
- Stomach content analysis – Studies examining the stomach contents of burrowing owls have found remains of ground squirrels and other rodents. One study in California found ground squirrels in 11% of burrowing owl stomachs analyzed.
- Observations of hunting – Burrowing owls have been directly observed hunting, killing and consuming ground squirrels above ground near their burrows.
- Remains near nests – The remains and bones of ground squirrels have been found near burrowing owl nests and burrows.
Researchers have used cameras near burrowing owl nests and have captured footage of adult owls carrying dead ground squirrels back to feed their young. So there is clear evidence that burrowing owls actively hunt and eat ground squirrels.
Ground Squirrels Are a Small Prey Item
However, studies show that ground squirrels make up a relatively small part of the overall diet. Burrowing owls are opportunistic predators and eat a wide variety of prey.
Some key facts about burrowing owls’ diet:
- Insects make up over 50% of their typical diet – including beetles, grasshoppers, moths and crickets.
- Small rodents make up around 25% of their diet.
- Ground squirrels comprise only about 11% of their rodent prey on average.
- They also eat other small birds, amphibians, reptiles and occasionally carrion.
So while burrowing owls certainly prey on ground squirrels, this represents a small fraction of their total food intake. Insects and other rodent species are more important food sources in most cases.
Relationship Between Burrowing Owls and Ground Squirrels
Beyond predator-prey dynamics, burrowing owls and ground squirrels have an ecological relationship that includes indirect competition, commensalism and mutualism:
Indirect Competition
Burrowing owls and ground squirrels sometimes compete indirectly for usable burrow space. Since they occupy the same underground nesting habitat, there can be competition where burrow availability is limited.
However, burrowing owls rarely dig their own burrows and so are dependent on abandoned ground squirrel burrows for nesting and shelter. This reduces direct confrontation over burrow space.
Commensalism
The use of ground squirrel burrows by burrowing owls is a commensal relationship – where one species benefits while the other is unaffected. Ground squirrels dig burrows for their own nesting and shelter. When ground squirrels abandon a burrow, owls move in and take advantage of the vacant burrow. So burrowing owls benefit, while ground squirrels are unchanged.
Mutualism
Both species likely benefit from the presence of the other through mutualism as well. For example:
- Owls and ground squirrels may provide each other early warning of approaching aerial or terrestrial predators.
- Their burrowing activity helps aerate and mix the soil, promoting plant growth.
- Scatter hoards of food by ground squirrels may provide scavenging opportunities for burrowing owls.
So the relationship has both competitive and cooperative components.
Hunting Interactions
When burrowing owls do prey directly on ground squirrels, there are some common hunting strategies and interactions:
Perch-Hunting
A frequent strategy is for burrowing owls to perch-hunt for ground squirrels from a slightly elevated perch like a fence post or rock. The owls watch for movement and dart down quickly to grab prey. Their long legs and wings give them speed and maneuverability on the ground.
Ambush Near Burrows
Owls will also hide and wait in ambush near active ground squirrel burrow entrances, waiting for an opportunity to strike. Ground squirrels have to remain vigilant when outside the burrow because an owl could be waiting unseen.
Striking From Cover
Burrowing owls sometimes conceal themselves at the edges of grassy vegetation and attack ground squirrels out in the open. Their camouflage plumage allows them to remain hidden until close distances.
Defense Against Predation
Ground squirrels have evolved several defenses against predation from burrowing owls and other predators:
- Alarm calls – Ground squirrels issue loud alarm calls when spotting a potential threat like an owl, warning others.
- Retreat to burrows – Ground squirrels quickly retreat into their burrow systems when alarmed.
- Mobbing – Ground squirrels may mob or harass owls near their burrows.
- Cautious foraging – Ground squirrels remain alert and keep watching for danger when out feeding.
So ground squirrels have behaviors to avoid falling prey to burrowing owls, though owls do sometimes succeed in ambushing them.
Population Effects
In areas where they coexist, what effects do burrowing owls have on ground squirrel populations through predation?
Limited Long-Term Impacts
In most cases, the predation pressure from burrowing owls does not significantly impact long-term ground squirrel populations. Some key reasons why:
- Owls selectively target juvenile squirrels – Adult squirrels are often too large for owls to overwhelm.
- Squirrels have high reproductive rates – Litters of 5-10 pups are common, offsetting predation.
- Owls take relatively few squirrels – Insects and other prey make up most of the owl diet.
- Many squirrels escape to burrows when attacked.
- Owl populations are generally stable, not rising disproportionately.
So even in locations with substantial owl populations, ground squirrel numbers remain resilient.
Localized Effects
However, there is some evidence of localized, temporary effects:
- Owls may temporarily depress very localized squirrel populations around nests through consistent predation.
- Squirrel density may be lower near owl nests compared to further away.
- Owl predation may skew squirrel populations to more adults.
- Effects disappear once owls migrate or owlets leave nests.
So very localized dips in ground squirrel numbers may occur around actively hunted owl nesting areas. But this is temporary.
Sympatric Populations
Overall, burrowing owls and ground squirrels thrive as sympatric populations, persisting and reproducing despite coexistence and owl predation. Neither species overly threatens the other’s broader regional population stability. The predator-prey dynamics appear sustainable.
Geographic Variations in Interactions
Across the broad overlapping range of burrowing owls and ground squirrels in North America, there are some geographic differences in the nature of their interactions and importance as prey:
Western Populations
In western states like California, ground squirrels make up a more significant proportion of burrowing owl diet:
- Up to 35% of prey in California.
- Likely due to higher squirrel densities in Lower 48.
- Higher reliance on ground squirrels in winter months.
So ground squirrels may be a key prey resource sustaining western wintering owl populations.
Midwestern Populations
In midwestern prairie regions, ground squirrels are a lesser diet component:
- Around 3-10% of total prey items.
- May reflect lower squirrel densities on northern Great Plains.
- Insects like grasshoppers are a prime prey target instead.
Here ground squirrels are a minor supplementary food source for owls.
Southern Populations
In southern regions like Texas, ground squirrels are significant prey for resident burrowing owl populations:
- Up to 45% of prey remains in Texas diet studies.
- Abundant ground squirrel populations in southern grasslands.
- Key year-round protein source for non-migratory owls.
So in the south, availability of ground squirrels helps support non-migratory owl populations.
Florida
In Florida, burrowing owls coexist not with ground squirrels but with the southeastern pocket gopher, which fills a similar niche. Studies show owls prey heavily on pocket gophers in Florida, relying on them as a prime food source equivalent to ground squirrels in the west.
Conservation Implications
The predator-prey relationship between burrowing owls and ground squirrels has some important conservation implications. Declines in either species can impact the other.
Burrowing Owl Declines
Many burrowing owl populations have declined due to habitat loss. Loss of ground squirrels could further threaten owls if alternate prey cannot compensate. Where ground squirrels are a vital food source, their conservation helps support sustainable owl populations. Protection of grassland ecosystems maintains interconnected owl and squirrel populations.
Ground Squirrel Declines
If ground squirrel populations significantly declined, burrowing owls could lose a valuable prey resource. Limited burrow availability could also displace owls. On the other hand, overly abundant ground squirrel populations resulting from elimination of predators like coyotes can degrade grasslands through overgrazing, which eventually negatively impacts owls. Balanced predator-prey interactions appear optimal for both species.
Reintroduction Programs
When reintroducing burrowing owls, care should be taken to select sites with healthy ground squirrel populations if they are a key part of the natural diet. Reintroduction success will be higher if adequate prey is available. Academic studies provide guidance on optimal squirrel densities to support owl populations.
Conclusion
In conclusion, burrowing owls do regularly prey upon ground squirrels as part of their natural diet across North America. However, predation rates are not severe enough to significantly impact broader ground squirrel population levels long-term in most regions, although localized and temporary declines may occur. Variations exist in how much owls rely on ground squirrels based on geography and ecosystem. Conservation of both species is interlinked, as ground squirrels provide burrowing owls with food and nesting resources. With balanced populations of predators and prey, burrowing owls and ground squirrels are able to persist in a stable state of sympatry across grassland habitats.
