There are a few small bird species that are known for their aggressive behavior towards other birds. The most notorious small birds that attack others are:
- Wrens
- Hummingbirds
- Sparrows
- Crows
These birds are often very territorial and will actively defend their nesting areas from intruders. While they are small in size, they can be surprisingly aggressive and fearless when it comes to confronting much larger birds that enter their territories.
Wrens
Wrens are feisty, noisy little birds that are known for their aggressive behavior. They are one of the smallest songbirds, typically measuring only 4-6 inches in length. However, they will vigorously defend their nesting territories from other birds that venture too close.
Some of the most aggressive wren species include:
- Carolina Wren
- House Wren
- Winter Wren
Wrens will chase, peck, and harass intruders relentlessly. They have even been known to mob birds of prey like hawks that get too close to their nests. Though wrens themselves often fall prey to larger birds, they will valiantly try to drive them away by dive-bombing them.
Carolina Wren
The Carolina Wren is a common backyard bird found in the eastern and southern United States. It is a loud, energetic bird with a distinct white eye stripe.
Carolina Wrens are extremely territorial all year long, not just during breeding season. They will aggressively defend their nesting areas from other wrens as well as larger birds like robins, jays, and even hawks. Both the male and female participate in these aggressive displays.
They have a variety of alarm calls and will loudly scold intruders. They may also puff up their bodies to appear larger and repeatedly dive bomb at the intruder. These feisty little birds do not hesitate to peck, jab, and flap their wings at much bigger birds.
House Wren
The House Wren is found throughout most of North and South America. It prefers to live around human habitations.
House Wrens are fiercely protective of their nesting territories. They will harass and attack other birds that enter their area, even larger birds like robins, jays, and doves.
Male House Wrens may build several “dummy nests” in their territory and will defend all of them aggressively even if they are unoccupied. They will scream at intruders and gape their mouths open to appear threatening. They may also peck and physically attack other birds.
House Wrens have been known to puncture the eggs of other bird nests within their territories. They may even kill hatchlings of other species.
Winter Wren
Winter Wrens are tiny, plump wrens that breed in forested areas of North America. They migrate to the southern U.S. and Mexico for winter.
Winter Wrens are fiercely territorial and remarkably pugnacious for their size. They will attack any birds that encroach on their breeding territory, especially other wrens.
They will chase, peck, scream, and flap their wings violently at intruders. They may repeatedly dive bomb much larger birds including jays, thrushes, and birds of prey. They are so aggressive that competing male wrens have been known to kill each other in extreme disputes.
Hummingbirds
Hummingbirds are the smallest birds on earth, but they are known for being fiercely territorial and attacking other hummingbirds that enter their space. Here are a few aggressive hummingbird species:
Anna’s Hummingbird
Native to western North America, Anna’s hummingbirds are known for their extreme aggressiveness towards intruders. Males are highly territorial and will defend their feeding areas from other males as well as larger birds.
They show intimidating displays like loud chirping, rapid buzzing flight patterns, and even physical attacks on other birds. They will chase away intruders by jabbing their sharp beaks, pecking wings, and bodily slamming into them at high speeds.
Rufous Hummingbird
The feisty Rufous hummingbird breeds farther north than any other hummingbird species. They are extremely aggressive in defending their breeding territories in northwestern forests.
Males will fight off other male hummingbirds from their territory by making intimidating display dives and chasing intruders. They use their needle-sharp beaks and claws as weapons. They have been known to tear out feathers and even kill competing males during fierce aerial attacks.
Black-chinned Hummingbird
Found in western North America, the Black-chinned hummingbird is known for its bad temper. They are aggressive defenders of flowers and feeders, attacking and chasing away any other hummers that approach these food sources in their territory.
Males will make spectacular display dives at intruders. They will also physically attack other hummers that don’t get the hint, using their beaks and claws to jab and scrape the intruder.
Sparrows
Many sparrow species are fiercely territorial of their nesting areas and will attack other birds that enter their space. Some aggressive sparrows include:
Song Sparrow
Song sparrows are widespread across North America. They are extremely territorial during breeding season, especially males defending their nesting sites.
Song sparrows will aggressively chase other birds away from their territory, especially other song sparrows. They may act distressed, make alarm calls, and display aggressive postures like wing-flicking. They will physically attack intruders with their beak and claws.
Chipping Sparrow
The small Chipping Sparrow breeds across Canada and the U.S. They are very defensive of their nesting areas.
Males will chase away other birds by flying at them with legs dangling, wings flicking, and loud calls. They may peck and claw at the heads of intruders. Females may also join in attacking trespassing birds.
White-crowned Sparrow
White-crowned Sparrows breed in Alaska and Canada and defend nesting territories aggressively. Males sing to mark their territories and will attack intruding sparrows.
They may pose a threat display, spreading wings and tail. Then they will chase and peck fiercely at the intruder, occasionally grappling in mid-air combat. Females have also been observed attacking trespassing birds.
Crows
Crows can be highly aggressive birds when defending their territories and nests. Some very aggressive crow species include:
American Crow
American crows are widespread across North America and very defensive of their nesting areas. They mob potential predators like hawks and owls in large, loud groups.
Crows may also attack other species that compete for their territory and food sources. Groups of crows may harass, chase, and peck at intruding birds until they leave the area.
Northwestern Crow
The Northwestern crow inhabits the northwest coast from Alaska to Oregon. They are very territorial birds who defend their coastal nesting areas aggressively.
Northwestern crows will chase, dive-bomb, and mob birds of prey or other intruders in raucous groups. They use loud, scolding calls and physical attacks with their sharp bills to harass unwanted birds.
Fish Crow
Fish crows reside along the east and Gulf coasts of North America. Their nesting colonies in coastal woodlands are aggressively defended.
Fish crows will form mobs and vigorously dive-bomb hawks, owls, eagles, and other potential nest predators. They use loud distress calls and their sharp bills to drive trespassing birds away.
Why Do Small Birds Attack Other Birds?
Small birds often attack other birds that intrude in their nesting territory for the following reasons:
- To defend food sources like feeders and fruiting trees/shrubs
- To defend their mate during breeding season
- To protect eggs and hatchlings in their nest
- To maintain ownership of prime nesting sites
- To establish dominance and breeding rights within a territory
Aggression towards intruders allows small birds to ensure their survival and reproductive success. Though they are tiny, small birds are fierce defenders of their territories and nests. Their aggressive behavior is driven by hormonal changes and instinct to protect essential resources needed to attract a mate, breed, and raise young.
How Do Small Birds Attack?
Though they are lightweight, small birds have an arsenal of aggressive tactics they use to attack intruders:
- Alarm calls & scolding – Harsh, loud calls to signal distress and warn the intruder
- Posturing – Puffy feathers, spread wings and tails to appear larger and more threatening
- Dive bombing – Rapidly swooping at the intruder from above
- Mobbing – A group of birds swarming and harassing the intruder
- Chasing – Flying rapidly at the trespassing bird to drive it away
- Pecking – Jabbing beak into intruder’s body
- Wing-flicking – Rapidly flicking wings against intruder
- Clawing – Scratching intruder with claws
The goal is to intimidate intruders and inflict enough pain/discomfort to get them to retreat from the territory. Though birds do sometimes die from injuries sustained in these attacks, more often the trespasser gets the hint and flees.
How Can Other Birds Protect Themselves?
Since small aggressive birds can’t always be deterred, here are some ways other birds can protect themselves from attacks:
- Have escape routes planned
- Get low to the ground and cover head with wings
- Allow subordinate birds in the group to absorb the attacks
- Flee quickly once attacked rather than freezing in place
- Avoid nesting areas occupied by aggressive species
- Nest high up in trees rather than low in bushes
- Build nests in dense, protective foliage
Staying alert and not lingering in territories with aggressive nesters will help prevent surprise attacks. Situational awareness and quick reflexes are key to avoiding injury. Most trespassers flea after an initial attack if given the chance.
Conclusion
Though tiny, many small bird species aggressively defend their territories and nests from intruders. Wrens, hummingbirds, sparrows, and crows are notorious for harassing, mobbing, and even injuring trespassers with surprisingly fierce attacks. Understanding what motivates nesting aggression and having defensive tactics prepared can help potential intruders avoid and flee attacks. Respecting boundaries is the best policy when dealing with feisty small birds.
