Squirrels and birds often coexist in suburban and urban areas, but their relationship is complex. On one hand, squirrels can provide benefits to birds by planting trees and dispersing seeds. However, they also compete with birds for food resources and nesting sites. Squirrels sometimes prey on birds’ eggs and young, but the overall impact on bird populations is likely small except in isolated cases.
Do squirrels eat bird eggs?
Squirrels are primarily herbivores, feeding on nuts, seeds, fruits, mushrooms, and sometimes young plant shoots. However, they are also opportunistic omnivores and have been known to eat bird eggs and nestlings in some cases. Several studies have documented squirrels raiding birds’ nests and eating eggs and baby birds, including songbirds, pigeons, doves, and ducks.
Some of the key research findings include:
- A study in Canada found that northern flying squirrels ate the eggs of boreal birds like warblers, thrushes, and finches. Predation rates ranged from 5-10% of nests. (1)
- Red squirrels have been filmed eating the eggs and young of marsh tits and willow tits in Finland. Up to 35% of nests were preyed upon in some habitat patches. (2)
- Fox squirrels were responsible for up to 67% of predation events on real and artificial nests monitored by researchers in Illinois. The squirrels preyed on eggs and nestlings of robins, cardinals, and finches. (3)
- A California study found evidence of squirrel predation in 10% of actual songbird nests, with the highest rates for yellow-rumped warblers and dark-eyed juncos. (4)
So in summary, while not a huge percentage of nests, squirrels do sometimes eat bird eggs and young. The extent likely depends on the squirrel species, abundance, and habitat.
Why do squirrels raid bird nests?
Squirrels are opportunistic foragers, so they will take advantage of any easily accessible source of nutrition. Birds’ eggs are high in protein and fat, making them a desirable food item. Squirrels also have flexible diets that allow them to switch to alternate food sources when their preferred foods become scarce. Some hypothesize that egg eating is more likely to happen just before or after winter, when nuts and seeds are less available.
In addition, bird nests may be vulnerable if they are built low to the ground or in open boxes or platforms. Squirrels are excellent climbers and can access many exposed nest locations. Their presence near human dwellings may bring them into closer contact with songbird nests.
Do squirrels target certain bird species?
Research shows squirrels will take eggs and nestlings from a wide variety of bird species. However, certain features may make some nests more vulnerable than others:
- Ground and low nests: Squirrels raid the nests of ground-nesting species like plovers, quail, and grouse. They also target open, exposed cup nests built low in shrubs and trees.
- Cavity nests: Squirrels can access the nests of cavity nesters like woodpeckers, nuthatches, swallows, and bluebirds if the cavity entrance is large enough.
- Artificial nesting sites: Manmade nest boxes and platforms may be easier for squirrels to get into compared to natural tree cavities.
- Unprotected nests: Squirrels are more likely to eat eggs in nests that are unattended by the adult birds.
With their versatile climbing skills, squirrels potentially threaten a wide range of low-nesting songbirds, pigeons, doves, gamebirds, and waterfowl. However, some birds may be more frequently targeted based on nest location and habits.
Do squirrels eat adult birds?
While squirrels sometimes eat bird eggs and nestlings, they very rarely prey on adult birds. Birds tend to be faster and more agile than squirrels, so they can usually escape from squirrel attacks. Additionally, adult birds have defensive behaviors like dive bombing or pecking that help protect them.
There are a few isolated reports of squirrels preying on injured, sick, or very young birds. For example, a case from the UK described an urban red squirrel killing and eating an infant pigeon that fell from its nest. However, healthy, full-grown birds are generally safe from hunting squirrels. Some types of squirrels may very occasionally eat small bird carcasses they find already dead.
Do squirrels attack feeder birds?
Squirrels are definitely attracted to bird feeders as an easy food source. However, they rarely directly attack adult birds at feeders. Their main food competition strategy is stealing seed directly from the feeder itself. In fact, studies show bird numbers and diversity actually increase at feeders used by squirrels, since they knock so much seed to the ground.
Squirrels prefer to avoid adult birds and mainly interact with them through competitive behavior like chasing them away from desired food sources. Their attacks focus on immobile eggs and nestlings rather than agile adult birds. So overall, while annoying feeder pests, squirrels do not seriously threaten most adult birds at feeders.
Effects of squirrels on bird populations
Most evidence indicates that squirrel predation has minimal impacts on overall bird populations, although localized effects on certain species may occur. Some key points:
- Predation rates on eggs/young are usually under 10-20%, not enough to destabilize populations. Birds can lay replacement clutches.
- Squirrels alone rarely drive declines. Other factors like habitat loss are bigger issues.
- Some susceptible species like grouse and plovers may suffer reduced breeding success in areas with high squirrel density.
- Squirrels are not a major threat for most common backyard birds and feeder species.
So while squirrels do opportunistically eat birds’ eggs and nestlings, most evidence indicates this does not have catastrophic effects on bird numbers overall. The bigger threat to many bird species remains habitat loss. However, localized management may sometimes be needed where squirrels overabundance threatens endangered ground-nesting species.
Positive effects of squirrels on birds
While they compete for some resources, squirrels also provide benefits for birds in some cases:
- Food provision: Squirrels help distribute seeds and nuts that birds then eat. They also drop food from bird feeders that birds can access.
- Tree planting: By burying nuts and seeds to store for later, squirrels inadvertently plant trees that grow to provide habitat and food sources for birds.
- Soil aeration: Squirrels’ digging behavior in pursuit of buried nuts and in building burrows helps aerate soil and distribute organic matter, promoting vegetation growth.
- Pest control: Squirrels eat insects and fungi that can damage trees. This protects trees that provide nest sites and food sources for birds.
So while competition definitely exists, squirrels are not universally bad for bird populations. Their unique ecological roles also provide some benefits in terms of habitat creation and food provision.
Ways squirrels compete with birds
Beyond direct predation, squirrels can affect birds through other competitive behaviors including:
Food theft
Squirrels are notorious for stealing from bird feeders, reducing access to supplemental food sources for birds. They also take buried food caches. a study in Canada found that red squirrels took 32-74% of seeds buried by the Clark’s nutcracker.
Nest site competition
Squirrels may take over cavities in trees and nest boxes intended for breeding birds. For example, flying squirrels often occupy nest boxes put out for ducks and eastern bluebirds in North America.
Displacement
Squirrels can displace birds from prime habitat through direct aggression or by depleting food resources. Grey squirrels in Europe have contributed to the decline of native red squirrels as well as some songbirds.
Transmission of diseases/parasites
Squirrels may potentially spread diseases and parasites to birds that share habitat with them. However, little research confirms transmission from squirrels to birds.
While competition exists, it remains difficult to quantify the population-level impact on birds from factors like nest site competition and food theft. The overall ecosystem influence of squirrels on birds is complex and context-dependent.
Solutions to reduce squirrel impact on birds
If high localized squirrel predation or competition is an issue, some potential solutions include:
- Remove any outdoor food sources like pet food that subsidize squirrel numbers.
- Use squirrel-deterrent feeders with weight-sensitive perches.
- Install predator guards or restrict entrance size on nest boxes.
- Use smooth metal collars to prevent squirrels climbing to nests.
- Plant vegetation to obscure nests from squirrel view.
- Protect individual nests with wire mesh or other physical barriers.
- Use taste or scent repellents on nests and eggs.
- Control squirrel overpopulation through trapping or other humane methods where permitted.
While eliminating natural food sources like nuts and seeds is not recommended, discouraging reliance on artificial feed can help limit squirrel density. Population control, physical deterrents, and vigilance during peak nesting can help reduce squirrel predation on vulnerable bird species.
Conclusion
Squirrels are sometimes predators of birds’ eggs and nestlings. However, research overall suggests minimal broad impacts on bird populations, except perhaps for some vulnerable ground-nesting species. Squirrels mainly opportunistically take eggs when other foods are scarce and bird nests are easily accessible.
Adult birds are rarely threatened by squirrels. While they compete for resources, squirrels also benefit birds indirectly by planting trees and providing food. A balanced ecosystem approach involves understanding the complex species interactions. In areas where squirrels are overabundant, management solutions like deterrents and population control can help reduce excessive predation rates on nesting birds.