Birds are not generally considered threatening, but even the smallest bird will defend its territory, in some cases intimidating and discouraging invaders that may be hundreds of times larger and heavier than the bird itself. Understanding the different threat displays birds use can help birders better recognize this type of behavior and help protect birds from unintentional stress.

Why Birds May Feel Threatened

Birds feel threatened whenever they perceive their basic needs or survival may be at risk from an intruder, competitor or predator.

This can apply to several aspects of survival, including…

• Food: A popular feeding station, nectar-rich flowerbed, productive berry bush, private cache of nuts, carrion carcass or any other type of food source may trigger a bird's territorial instincts, and if that food is encroached upon, a bird may use threat displays to ward off the competition.
   
• Territory: Birds make a great effort to claim territory that meets their needs, and they will defend that territory as long as they need it. For migratory species, their defense may wane after the breeding season, but if the birds stay in the same range year-round, they may use threat displays throughout the year.
   
• Mates: Birds are always seeking the most impressive mate to pass their genes along to the next generation, but if their mate receives attention from a competitor, the first bird may use threat displays against the interloper to strengthen their initial claim and breeding rights.
   
• Nest: Birds can be especially aggressive during the breeding season and will use a variety of threat displays near their nest, often with increasing intensity as the nest is more strongly threatened or disturbed. This agitation may begin when the nest is under construction and continue until the brood has fledged and there are no more parental duties.
   

• Chicks: Parent birds are dedicated to protecting their offspring, and even after young birds have first left the nest, the parents will continue to guard them until the chicks are mature enough to effectively fend for themselves.

Types of Bird Threat Displays

Birds may use either passive or active displays to deter intruders and predators. Passive displays are more dependent on camouflage and are often used by birds that are heavily preyed upon by other animals, while active displays are more energetic tactics to discourage unwanted visitors.

Passive threat reactions and displays include…

• Camouflaged Posture: Birds with camouflaged plumage may adopt stealthy postures when threatened in order to confuse predators. An American bittern, for example, will stretch out its streaked neck to blend in with marsh reeds, while different potoos will raise their heads to blend in with bark patterns in the trees where they roost.
   
• Confusing Plumage: Some birds have uniquely deceptive markings that can discourage predators without any extensive effort. Many small owls, for example, have eyespots on the back of their heads to confuse predators into thinking they have been spotted, thereby discouraging rear attacks.
   
• Freeze Postures: Because predators see motion much more easily than an object at rest, many game birds and other common prey birds freeze when they feel threatened. This can help their plumage blend into the surroundings, further increasing their camouflage and confusing predators.

When a passive action isn't enough for a bird to protect itself, more active, aggressive threat displays may be necessary, such as:

• Changing Size: A larger, more robust bird can often intimidate an intruder, and many birds fluff their plumage, spread their wings, droop their tails or otherwise adjust their feathers or posture to give an impression of larger size to stave off a predator or other unwanted guest.
   
• Color Display: Bright colors such as red, orange, yellow and white are warning signals to many animals, and birds will use those colors in their plumage as threat displays. The northern mockingbird, for example, will raise its wings to show off prominent white patches as a threat, while ruby-crowned kinglets raise their bright red crowns when agitated.
   
• Sounds: Vocal threats are common among birds and include loud, robust singing or specialized alarm calls, hisses or other vocalizations. Bill clacks, drumming or wing claps might also be part of the sound displays birds use to defend their territory and keep intruders away.
   
• Slow Motion: Slow, deliberate motions can be very intimidating to predators, letting them know they have been spotted and any element of surprise in their attack is lost. Birds may use bobbing, weaving or similar displays to convey their threat, and at the same time those displays help the birds get a better look or hear the intruder better so they can be more protected.
   
• Chasing: Energetic birds will eagerly chase intruders out of their territory, often pursuing them through erratic patterns or well beyond their territorial borders to ensure they have left the vicinity. These chases are often accompanied by vocal threat displays as well.
   
• Mobbing: Gregarious birds often use group tactics against intruders, including ganging up on an interloper and mobbing it until it leaves the territory. This may include vocal harassment, chasing or even attacking the intruder from multiple directions to confuse and disorient it, encouraging it to leave even more quickly.
   
• Attacks: Even small birds can be fierce fighters when they feel threatened, and they may attack with their bills, talons or wings as they dive at intruders. Flightless birds may kick when threatened, and birds with broad wings, such as many large waterfowl, will vigorously flap to beat at their opponents.

With so many different threat displays to use, birds are well able to defend themselves and discourage intrusions from unwanted visitors.

When a Bird Threatens a Birder

It can be fascinating for a birder to witness different threat displays firsthand, but it is important to note that the birder themselves is often the cause of a bird's distress, and very aggressive birds may even attack birders if they feel the human is presenting a dire threat. Whenever a bird is so obviously stressed, a conscientious birder should quickly and carefully retreat. Ultimately, no matter how intriguing a bird's behavior may be, it is always best for birders to keep their distance and allow birds to enjoy their territories and activities without stress.

Photo – Golden-Crowned Kinglet © Francesco Veronesi