Spotted owls are medium-sized owls that live in forests in western North America. Their diet consists primarily of small mammals, birds, and insects. Understanding what spotted owls eat is important for conservation efforts, as these owls are threatened in some parts of their range.
Quick Facts on Spotted Owl Diet
- Spotted owls are carnivores that hunt small prey at night.
- Their main prey items include mice, voles, rats, gophers, and squirrels.
- They also eat birds such as woodpeckers, robins, and jays.
- Insects like beetles, crickets, and moths make up a small portion of their diet.
- Spotted owls swallow their prey whole and regurgitate pellets of undigested material.
- Their hunting success rate is estimated to be around 50%.
Mammal Prey
Small mammals make up the bulk of the spotted owl’s diet. Important mammalian prey species include:
- Deer mice
- Red tree voles
- Northern flying squirrels
- Bushy-tailed woodrats
- Pocket gophers
- Chipmunks
- Shrews
These small mammals are abundant in the forests inhabited by spotted owls. Spotted owls hunt by perching on tree branches and swooping down on prey moving on the ground. Their exceptional hearing allows them to precisely locate prey in the dark.
Deer Mice
Deer mice are one of the most common prey items for spotted owls. These small rodents have high reproductive rates, allowing their populations to withstand owl predation. Deer mice feed on seeds, fruits, fungi, and arthropods.
Red Tree Voles
The arboreal red tree vole is an important source of prey for spotted owls in the Pacific Northwest. Spotted owls pluck these voles from the cavities and nests they build in trees. Red tree voles mainly eat conifer needles.
Northern Flying Squirrels
Northern flying squirrels are another tree-dwelling rodent consumed by spotted owls. Their ability to glide between trees helps them evade predators, but they still fall victim to the owls’ efficient hunting. Flying squirrels primarily eat fungi, lichens, fruits, and seeds.
Woodrats
Woodrats, also known as packrats or trade rats, make up a decent portion of the spotted owl’s diet in drier forests. They build large stick nests, which provide cover but also make them vulnerable when spotted owls hunt at night. Woodrats are mostly herbivorous, feeding on leaves, twigs, and cacti.
Bird Prey
Though mammals dominate their diet, spotted owls also prey on a variety of small birds, mainly songbirds but also woodpeckers and smaller owls. Some bird prey species include:
- Steller’s jays
- American robins
- Common flickers
- Downy woodpeckers
- Dark-eyed juncos
- Chestnut-backed chickadees
- Northern pygmy owls
Spotted owls capture resting birds and raid nests for eggs and nestlings. Birds provide an important alternate prey source when mammal populations decline. The owls help control songbird and woodpecker populations in forest ecosystems.
Steller’s Jays
These bold blue jays are vulnerable to predation when roosting at night. Steller’s jays occupy similar forest habitat as spotted owls across much of their range. Jays sometimes mob owls during the day in an attempt to drive them away from nests.
American Robins
Ground-foraging American robins are a common food source for spotted owls. Robins eat earthworms, insects, and fruit from trees and shrubs. Their numbers increase in spring and summer when owls prey on adults, eggs, and nestlings.
Woodpeckers
Several species of woodpeckers are natural prey for spotted owls. They pluck adult, young, and eggs from tree cavities when woodpeckers are inactive at night. Downy woodpeckers and common flickers are two of the most commonly taken woodpecker species.
Insect Prey
While not a major food source, spotted owls do consume some insects to supplement their diet. Some insect prey include:
- Beetles
- Crickets
- Grasshoppers
- Cicadas
- Moths
- Caterpillars
- Centipedes
- Spiders
Spotted owls seem to favor large insects like beetles, crickets, and grasshoppers. Insects likely become more important in the diet during the summer months when they are abundant. The owls capture flying insects on the wing and pluck crawling ones from vegetation.
Beetles
Ground beetles, longhorn beetles, and wood-boring beetles are attracted to the forests occupied by spotted owls. The owls opportunistically grab these insects to supplement their small mammal diet. Some beetle species may be distasteful or difficult for the owls to digest.
Crickets and Grasshoppers
Crickets and grasshoppers are an excellent source of protein, fat, and calories for spotted owls. These insects are nocturnal and provide easy pickings as they roost on plants at night. Crickets and grasshoppers thrive during warmer months when owl insect consumption increases.
Moths
Moths make up a portion of the spotted owl’s insect intake. They likely snatch slower-flying moths more often than faster species. Abundant moth populations in certain years like outbreaks of tent caterpillars allow owls to prey on them readily.
Other Prey
Beyond mammals, birds, and insects, spotted owls occasionally consume other prey including:
- Bats
- Reptiles and amphibians
- Other small birds and owls
- Fish
- Carrion
However, these food sources comprise a very minor amount of the owl’s total diet. For example, bats may occasionally roost where they are vulnerable to the owls. But bats detect and evade owl attacks much more often than not.
Hunting and Feeding
Spotted owls are sit-and-wait predators. They perch on branches close to the ends of tree canopies and swoop down on prey detected through sound and movement. The owls use their large talons to grab prey and sharp beaks to rip it apart. They swallow small prey whole.
Spotted owls typically hunt along habitat edges where prey density is higher. They have keen night vision from large, forward-facing eyes. Sensitive feathers around their face help spot prey direction. The owls can snatch prey in complete darkness by zeroing in on faint sounds.
On average, spotted owls consume 1-4 small prey items per day. However, they can go days between successful hunts. Digestion is relatively slow so the owls can go periods without eating. They hunt most actively on moonlit nights when increased light improves prey detection.
Spotted owls are primarily nocturnal but can opportunistically hunt diurnal species during the day like woodpeckers and robins. They cache extra food in tree cavities to eat later. Cached prey provides insurance against lean foraging nights.
Digestion
After catching and eating prey, spotted owls regurgitate pellets of undigested material like bones, hair, and feathers. Owl pellets provide useful information about their diet composition. However, pellets don’t indicate exact prey proportions since they differentially contain indigestible prey parts.
The owls’ stomach digestive acids dissolve the flesh of swallowed prey. Small prey is digested rapidly within 6-8 hours. Larger prey and larger meals take 12-24 hours to fully digest. The protein-rich diet supplies spotted owls with needed amino acids.
Digestion produces metabolic water to offset the relative aridity of the owl’s environment. Like other birds, their urine is expelled as semisolid uric acid rather than liquid urea. This helps conserve much needed water and electrolytes from prey flesh.
Diet Variation
Spotted owl diets can vary across different regions and forest types:
| Region | Primary Prey |
| Pacific Northwest | Northern flying squirrels, red tree voles, woodrats, deer mice |
| California Coast | Woodrats, kangaroo rats, pocket mice, deer mice |
| Sierra Nevada | Northern flying squirrels, chickarees, woodrats, pocket gophers |
| Canada | Red-backed voles, deer mice, shrews, jumping mice |
Diet also shifts seasonally with changing prey availability. For example, woodrats can become more prevalent in the diet during drier seasonal conditions. Birds and insects generally increase in spring and summer months.
Prey Selection
Spotted owls are opportunistic predators that target common small mammal and bird species. Their prey selection is mainly driven by:
- Abundance – Owls take prey that is readily available like deer mice and voles.
- Vulnerability – Selection favors prey that is active at night near the forest floor.
- Calories – Energy-dense prey like squirrels and voles are key food sources.
- Size – Optimal prey weighs 20-150 g, small enough to swallow whole.
The owls focus on nocturnal prey near the edges of openings in forest canopy cover. This habitat supports highest prey density while providing ambush perches for the owls.
Prey Populations
Small mammal populations are somewhat stable from year to year. But cycles and crashes can occur in some prey species like voles and gophers. This can significantly impact spotted owl nutrition in low prey years.
Owl predation alone exerts only modest pressure on prey numbers. Other mortality factors like disease, starvation, and additional predators combine to control populations. The high reproductive rates of most prey species compensate for overall losses.
Forest logging and habitat alteration can depress prey populations by reducing cover and foraging sites. Prey diversity provides insurance against shortages in any one species. Spotted owls switch between key prey sources depending on relative abundance.
Competition
Spotted owls share habitat and prey with several potential competitors:
- Barred owls – invasive relative that has displaced spotted owls in some regions
- Great horned owls – powerful owl that dominates higher quality habitat
- Northern goshawks – fierce diurnal raptor, competes for forest birds and mammals
- Bobcats – major small mammal predator that overlaps with owl habitat
- Coyotes – adaptable canid that takes small prey in wooded areas
Territorial spotted owls may manage competition by excluding other predators from occupied home ranges. They also partition prey resources temporally by hunting more nocturnally.
Cannibalism
Cases of cannibalism have been documented in spotted owls. Older juveniles and adult males occasionally prey on younger siblings. This supplemental food source may enhance survival when prey is scarce.
Cannibalism primarily occurs early in the breeding season before alternative prey is widely available. Owls in poor condition entering the breeding period are more likely to consume siblings and offspring. Removing some young may optimize feeding of remaining chicks.
Threats from Declining Prey
Spotted owl survival and reproduction are closely tied to prey abundance. Owls can experience starvation and reproductive failure in years when prey crashes. They may abandon nests and territories when unable to adequately provision offspring.
Forest management activities like clear cutting and short rotation logging can negatively impact small mammal and songbird prey communities. Fragmentation degrades habitat and reduces food resources within spotted owl territories.
Prey loss to invasive barred owls is another emerging threat. Barred owls exert predatory pressure on the same prey base as spotted owls. Conservation of key prey species is vital for the spotted owl’s future.
Importance of Diverse Prey
A diverse prey base is critical to sustain spotted owl populations. Multiple small mammal and bird species provide dietary stability and choice. Prey diversity limits the impacts of fluctuations in any single species.
Owls can compensate when one prey source declines by switching to alternate abundant prey. Diverse prey also provides a balanced nutritional profile to maintain growth and health. Management that encourages understory complexity is beneficial.
Conclusion
In summary, spotted owls are dietary generalists adapted to hunting a variety of small forest mammals, birds, and insects. Small nocturnal mammals like deer mice, voles, squirrels, and woodrats make up the bulk of their diet. Birds become important alternative prey during spring and summer. Distribution and abundance of these key prey species drive spotted owl foraging patterns and habitat use. Protecting sufficient prey resources is essential for the viability of their remaining populations.
