Last updated on May 28th, 2023 at 03:57 pm
Competition drives everything in the animal kingdom. Birds are in competition for limited resources, like nectar and food sources, nest sites, and females to mate with.
This is why it is quite common to see birds of the same species fighting, especially during the spring when it is courtship and nesting season.
Male birds of the same species chase and attack each other in competition for territory, food, and mating rights. To defend their nests from predators and brood parasites, birds behave aggressively towards other birds. Birds of prey are often attacked by smaller birds trying to defend themselves.
This Is Why Birds Attack Other Birds
One of the most interesting parts of birdwatching is interpreting what certain behaviors mean.
There are 4 main reasons why birds act aggressively towards one another:
- Competition for a mate
- Territorial behavior
- Predation and defense
- Birds attack nest robbers
1. Competition For Mates Causes Male Birds To Fight
Birds may attack each other due to intraspecies competition for mates. There are generally more males in a bird population than females.
Therefore, once a male has successfully enticed a mate, he must guard her against other males to ensure that his sperm fertilizes her eggs.
Most bird species breed in the spring, and this is usually the time you are most likely to see birds of the same species attacking one another.
Male birds have to compete for the right to mate with females.
This ensures that only the strongest, fittest, healthiest males pass on their genes to the next generation.
Birds of the same species do not often physically attack one another – the risk to both parties is too great.
Instead, males vocalize frantically and chase their competitors away.
2. Territorial Aggression Between Birds
Many bird species are territorial by nature, defending a certain area within their home range.
Once birds have established their territories, they aggressively defend them from rival males.
Territoriality is most common in songbirds, like warblers, thrushes, wrens, and larks.
Males who hold territories with better nest sites and more nectar and food resources will have more mating success than less dominant males.
They will mate with more females, therefore passing more of their genes on to the next generation.
Territoriality and aggression are traits that are sexually selected for in a species because the males that defend their territory most successfully mate with the females and pass on their genes.
Hummingbirds are well known for their territoriality. Ruby-throated and Rufous hummingbirds are particularly aggressive towards rival males.
They vocalize loudly and chase one another at high speed.
3. Predatory Birds Attack Other Birds
Birds of prey attack other birds to make a meal of them.
Vultures, falcons, hawks, kites, buzzards, crows, ravens, eagles, and owls all predate on other bird species.
Collectively, these species are called avian avivores.
These birds have a range of hunting tactics. Some, like the Eurasian sparrowhawk and the sharp-shinned hawk, are ambush predators.
They hide in trees and bushes, and when smaller birds fly past, they launch their attack.
Birds that can fly at high speeds, like falcons, are adapted to hunting on the wing.
Lanner falcons pursue their prey in vast, open spaces by chasing them horizontally across the sky.
In contrast, Peregrine falcons fly at a very high altitude, and when they spot potential prey, they dive to attack at extremely high speeds of over 300km/h!
These aerial chases and bombardments are fascinating to watch and make for incredible bird sightings.
4. Birds Attack Nest Robbers
Predatory birds like crows, ravens, magpies, jackdaws, rooks, and jays will rob other species’ nests, eating the eggs or the hatchlings.
These nest robbers are often attacked or mobbed by other birds in a frantic effort to defend their young.
It is quite common to see a larger bird being attacked and chased by a single bird or a group of smaller birds. This behavior is known as mobbing.
Mobbing happens all year round, but is it most common to observe during spring and early summer – most birds’ breeding season.
Many bird species, like chickadees, jays, blackbirds, titmice, kingbirds, and grackles, use mobbing as a defensive strategy.
Small birds will valiantly mob raptors, like falcons, hawks, eagles, and owls. It is also common to see crows and ravens mobbing larger birds of prey.
Birds of different species will join forces against a common enemy.
They work together to drive the threat away from their territory, chasing, dive-bombing, and even striking their target.
But why does the larger bird not defend itself?
Mobbing rarely harms the target, and it would be more energetically expensive for the larger bird to defend themselves from their assailants rather than just leaving the area.
While it may look like the smaller birds are doing something very courageous, they are in very little danger of being attacked by the target of the mob.
Smaller species are faster and much more agile than larger birds.
Sometimes Mating Can Look Like An Attack
If you are new to birdwatching, it can be difficult to distinguish mating behavior from an aggressive attack.
All you see is one bird descending on another and a flutter of wings!
Here are a few tips to tell mating from fighting:
- Generally, fights between birds are male-on-male. If you can tell the sex of the bird species, you can easily tell if they are mating or fighting. If it is a male and a female, they are most likely mating.
- The noise level is a very good indicator – fights are usually loud, with lots of frantic movement and vocalization. Mating behavior is typically much quieter. After the male has successfully done his courtship ritual, the mating happens quickly and without much noise.
What Are The Most Aggressive Bird Species?
The following birds most commonly fight amongst their kind or attack other species:
- American Crow
- American Coot
- Cassowary
- Great Horned Owl
- Mute Swan
- Northern Goshawk
- Northern Mockingbird
- Pine Siskin
- Ruby-Crowned Kinglet
- Rufous Hummingbird
- Wild Turkey