The northern goshawk (Accipiter gentilis) is a large bird of prey that inhabits forested areas across North America, Europe, and Asia. As an apex predator, the goshawk plays an important role in controlling populations of its prey species. Goshawks are powerful hunters with a varied diet, preying on birds, mammals, reptiles, and insects. Understanding the goshawk’s key prey species provides insights into its ecological relationships and how changes in prey abundance may impact goshawk populations.
Birds as Prey
Birds make up a significant portion of the goshawk’s diet, especially during nesting season when goshawks need a stable source of food to feed their chicks. Goshawks often target medium-sized birds that live or forage in forest habitats. Common avian prey includes:
– Grouse: Ruffed, spruce, blue, and sharp-tailed grouse are frequently taken by goshawks across North America. Grouse spend much of their time feeding on the forest floor, making them vulnerable to an ambush from above.
– Woodpeckers: Downy, hairy, northern flicker, and pileated woodpeckers are preyed upon by goshawks, especially in winter when other food sources are scarce. Their chiseling makes it easy for goshawks to locate them.
– Jays: Steller’s jays, blue jays, and gray jays are vulnerable to goshawk predation. Their noisy habits give away their location.
– Doves: Mourning doves and band-tailed pigeons are preyed upon where they overlap with goshawk habitat. Their ground-feeding habits expose them to ambush.
– Corvids: Crows, ravens, magpies, and jays are frequent goshawk kills, as they are abundant forest birds.
– Wood Warblers: Warblers that forage low in trees and shrubs like orange-crowned and Wilson’s warblers are preyed upon in migration and in summer.
– Sparrows and finches: Seed-eating birds like pine siskins, goldfinches, and various sparrow species become goshawk prey when feeding on the ground.
Characteristics of Avian Prey
Goshawks target birds that spend much of their time on or near the ground in forest habitats. The goshawk’s swift, low flight through crowded forests allows it to surprise ground-feeding species. Birds that advertise their location by being noisy or conspicuous also make easier prey. Smaller passerines are taken more often by male goshawks, while larger female goshawks can capture bigger quarry like grouse and corvids.
Mammals as Prey
Goshawks opportunistically prey on a variety of small mammals including:
– Squirrels: Tree squirrels like red, grey, and flying squirrels are vulnerable when they leave the trees to feed on seeds and fungi. Ground squirrels are ambushed from above.
– Rabbits and hares: Snowshoe hares are a major prey item in boreal forests. Cottontails, jackrabbits, and pika are also taken. Their tendency to freeze in place makes them an easy target.
– Woodland rodents: Mice, voles, chipmunks, and other small rodents are readily caught by goshawks when moving through forest cover.
– Opossums: These nocturnal mammals fall victim to goshawks when active during daytime.
Larger mammals like raccoons, skunks, and foxes may be preyed upon when young. Squirrels and rabbits make up the bulk of mammalian prey. Their tree and ground habits overlap with goshawk hunting strategies.
Characteristics of Mammalian Prey
Goshawks take mammals predominantly from the ground layer of forests. Quick, evasive species like adult squirrels can be difficult prey. Slow, unwary mammals like opossums make for easy captures. Nocturnal and crepuscular mammals are most vulnerable when active during daylight. Younger, smaller individuals of larger mammal species are more likely to be targeted than healthy adults.
Reptiles and Amphibians as Prey
Reptiles and amphibians are a minor component of the goshawk diet:
– Snakes: Garter snakes are most likely to be captured but other small snake species are also taken.
– Lizards: Northern alligator lizards and smaller skinks fall prey more frequently than large lizards.
– Frogs and Toads: Tree frogs and terrestrial amphibians are most vulnerable around wetlands.
Herpetofauna tend to be preyed upon opportunistically by goshawks during their seasonal activity periods. When abundant they can be a useful food source.
Characteristics of Reptilian and Amphibian Prey
Goshawks target slow-moving reptiles and amphibians that can be easily captured on the forest floor or in adjacent wetlands. Species that rely on camouflage for defense make ideal prey. Small individuals are most frequently taken. Large or toxic species are avoided. Herpetofauna do not typically make up a major part of the diet.
Insects and Other Invertebrates as Prey
During the summer, goshawks will opportunistically prey on large insects and other invertebrates:
– Beetles: Ground beetles, longhorn beetles, and scarab beetles are captured when visible on tree trunks.
– Butterflies: Larger species like swallowtails and monarchs are taken when feeding in sunlight openings.
– Dragonflies: Large dragonfly species are snatched in flight or captured resting on branches over water.
– Grasshoppers: These leaping insects are caught when they land after flights.
– Crayfish: These freshwater crustaceans are prey when captured out of streams and ponds.
Insects do not make up a large portion of the diet but provide useful nutrients.
Characteristics of Invertebrate Prey
Goshawks prey on larger insects that are visible during daytime activity. Slower moving species like beetles are easier to capture than flies. Prey is often captured during vulnerable periods like molting or mating. Destructive invertebrates like tent caterpillars may be selectively targeted. Insects become a more frequent prey item during summer.
Variation in Prey Across the Range
Goshawk prey availability changes across its range based on habitat and the animal communities present:
– Western forests: Grouse, squirrels, woodrats, corvids, woodpeckers and jays are key prey.
– Eastern forests: Squirrels, rabbits, jays, thrushes, and woodpeckers are more commonly taken.
– Boreal forests: Grouse, hares, corvids and woodpeckers make up the majority of prey.
– Eurasia: Pheasants, corvids, pigeons, thrushes and magpies are more frequent prey species.
While there is variation, bird species make up at least 50% of the diet across all parts of the goshawk’s range. Mammalian prey increases in importance at higher latitudes.
Causes of Geographic Differences
The differences in goshawk prey across regions reflect:
– Habitat variation – Prey availability follows forest type
– Latitudinal species diversity – Higher diversity near equator
– Species introductions – Non-native game birds expanded prey options
– Competitors – Great horned owls limit goshawks in some areas
– Prey population cycles – Hare abundance fluctuates
Goshawks are dietary generalists, able to shift prey seasonally and regionally based on what is available.
Threats to Goshawk Prey Populations
Declines in goshawk prey populations can threaten their breeding success. Some key dangers include:
– Habitat loss – Fragmentation of forests reduces prey numbers
– Climate change – Alters forest composition, disrupting food webs
– Overhunting – Hunting pressure can crash grouse/hare populations
– Pesticides – Rodenticides and insecticides reduce prey abundance
– Introduced predators – Domestic cats predate songbirds
– Disease – West Nile Virus has killed corvids like jays and crows
Consequences of Prey Loss
Low prey abundance causes goshawk breeding failures:
– Fewer nest attempts
– Smaller clutch sizes
– Increased chick mortality
– Declines in adult survival
– Eventual population declines
Sufficient prey is key to goshawk reproduction and population stability.
Conclusion
Northern goshawks prey on a wide array of forest-dwelling birds, mammals, reptiles and insects. Grouse, squirrels, corvids, and rabbits/hares are important prey groups across the range. Prey selection varies seasonally, regionally, and individually based on availability. Declines in key prey due to habitat loss, overhunting, climate change, and other threats can reduce goshawk reproductive success and stability. Maintaining abundant and diverse prey is crucial for the persistence of healthy goshawk populations into the future.