Crossbills are small finch-like birds that are found across North America, Europe, and Asia. They are named for their unique crossed bills, which allow them to efficiently pry seeds out of conifer cones. Crossbills play an important ecological role in disseminating seeds from conifers like pine, spruce, and fir trees. However, crossbills also face predation from a variety of animals.
Birds of prey
One of the main predators of crossbills are birds of prey, including hawks, eagles, falcons, and owls. These raptors hunt crossbills in flight or ambush them while they are feeding in trees. Some species known to prey on crossbills include:
- Sharp-shinned hawks
- Cooper’s hawks
- Northern goshawks
- Red-tailed hawks
- Golden eagles
- Peregrine falcons
- Great horned owls
- Northern saw-whet owls
Birds of prey use their keen eyesight, stealth, and speed to catch crossbills. They often pluck crossbills out of the air or snatch them from tree branches before the crossbills even detect them. Raptors are able to swiftly kill crossbills with their powerful talons. They usually eat the crossbill whole or rip it apart to consume.
Other predatory birds
In addition to raptors, some other bird species prey on crossbills, including:
- Crows
- Blue jays
- Ravens
- Magpies
- Jaegers
These birds are opportunistic and will eat eggs, nestlings, and occasionally adult crossbills when they get the chance. Crows, jays, and ravens sometimes raid crossbill nests for eggs and chicks. Jaegers are falcon-like birds that pursue crossbills in flight. While not as swift and powerful as birds of prey, these predatory birds still pose a regular threat to crossbills.
Squirrels
Tree squirrels, including American red squirrels and Douglas squirrels, are known to eat crossbill eggs and nestlings. Squirrels raid crossbill nests in conifers and consume the eggs and defenseless chicks. This usually happens when the parent crossbills are away from the nest gathering food. Squirrels are stealthy, quick, and able to access nests high in the tree canopy.
Snakes
Some snakes prey on eggs and nestlings in crossbill nests, including:
- Gopher snakes
- Racer snakes
- Rat snakes
- Pine snakes
Like squirrels, snakes raid nests to consume eggs and chicks when parent crossbills are absent. Snakes are able to scale trees and shrubs using their muscular bodies. They swallow eggs and chicks whole.
Chipmunks
Chipmunks are opportunistic foragers and will sometimes eat crossbill eggs or nestlings if they come across a nest. However, they do not seem to deliberately seek out crossbill nests. Chipmunks mainly feed on seeds, nuts, and fruit but are known to occasionally prey on bird nests.
Weasels
Small weasels like least weasels and ermine are agile predators that can climb trees and access crossbill nests. They are likely one of the most significant predators of eggs and nestlings along with squirrels and snakes. Weasels will consume the nutritious eggs and defenseless nestlings.
Bears
Bears like black bears and grizzly bears sometimes feed on crossbill eggs and chicks they come across while foraging in trees. Bears are able to reach nests, even quite high up, by standing on their hind legs and using their long limbs and claws. The eggs and chicks provide a high-calorie snack.
House cats
Domestic cats allowed to roam outdoors occasionally stalk and kill adult crossbills and may raid low nests. Crossbills foraging on the ground are especially vulnerable. Cats inflict lethal wounds with their teeth and claws. However, the impact of house cats on crossbill populations is likely minor compared to wild predators.
Other predators
Some other animals that opportunistically prey on crossbills include:
- Foxes
- Bobcats
- Fishers
- Martens
- Minks
These predators feed on crossbills when they are able to capture them but do not actively hunt them often. Crossbills comprise a small portion of their diets.
Relative threat of different predators
| Predator | Threat to eggs/nestlings | Threat to adults |
|---|---|---|
| Birds of prey | Medium | High |
| Crows/jays | Medium | Low |
| Squirrels | High | Low |
| Snakes | Medium | Low |
| Chipmunks | Low | Low |
| Weasels | High | Low |
| Bears | Medium | Low |
| Cats | Low | Low |
This table provides a general overview of the relative threat levels posed by key crossbill predators. As shown, birds of prey are the most significant predators of adult crossbills, regularly hunting them in mid-air. Squirrels and weasels pose the greatest dangers to vulnerable eggs and nestlings as they frequently raid nests when parents are away. Other predators feed on crossbills opportunistically, but do not heavily rely on them as a food source.
Anti-predator adaptations
Crossbills have evolved several key adaptations to help them evade predators:
- Camouflage – Their mottled brown, green, and gray plumage helps disguise crossbills in conifer trees.
- Flocking behavior – Crossbills gather in large nomadic flocks which helps detect predators earlier through increased vigilance.
- Nest concealment – They hide their nests in dense conifer foliage which helps protect from predators.
- Distraction displays – When predators approach a nest, parent crossbills use alarm calls and distraction displays to draw the threat away.
- Unpredictable flight – Their fast, irregular flight patterns make them harder for raptors to pursue and catch.
These adaptations likely evolved in response to heavy predation pressure from raptors, squirrels, snakes, and other nest predators over the millennia. They help adult crossbills evade predators and give eggs and nestlings somewhat greater odds of survival.
Impacts on population
Despite anti-predator defenses, predators likely kill large numbers of adult crossbills each year and consume many eggs and nestlings. However, crossbill populations remain abundant and widespread. Their high reproductive rate helps offset losses to predators. On average crossbills lay 3-4 eggs per clutch and can raise 2-3 broods per year.
While predation has a significant impact on individual crossbills, it does not seem to threaten the overall crossbill population. Their resilient numbers and high fecundity provide a buffer against predator losses. Crossbills are well-adapted to coexist with the variety of predators they have long interacted with in the coniferous forest ecosystems they inhabit.
Conclusion
Crossbills face predation from a diverse array of animals including raptors, corvids, squirrels, snakes, and weasels. The greatest threats come from agile predators like birds of prey and squirrels that hunt adults or raid nests for eggs and nestlings. However, crossbills have evolved adaptations like camouflage, flocking, and irregular flight to reduce attacks. While many crossbills fall victim to predators each year, their high reproductive capacity allows their populations to persist and thrive across boreal forest regions alongside these natural predators.
