Why backyard birds gang up on snakes during breeding season

The behavior of many birds flying around noisily and chasing after a snake can appear quite chaotic. However, in many yards and wetlands, this kind of behavior happens during the mating and breeding seasons, when bird nests contain eggs and chicks. Based on findings made by animal experts, this does not necessarily mean that the birds are exhibiting a panic response.

Instead, what is happening is called 'mobbing,' where birds use this technique to protect their eggs and young ones from any predators that might attack their nest, especially snakes. It appears that the reactions of birds increase greatly depending on the presence of chicks in the nests, and it increases during the breeding season.

Why do snakes make birds do this?


Birds do not react to all predators with such intensity. Studies about the behavior of the Japanese tit, presented in the Proceedings of the Royal Society B journal, show that birds make different kinds of calls based on their threats. Upon hearing alarm calls concerning a snake threat, birds instantly engaged in search behavior and assembled themselves around the threat region.

This kind of discovery confirms that these birds do not produce sounds out of fear, but rather they are trying to exchange some information among themselves. The vocal communication system of the Japanese tit reveals that animal communication abilities to send certain information about their enemy through an alarm call. It is necessary to admit that snakes represent additional danger, especially when located close to a nest, because in this way, they have an opportunity to consume eggs as well as offspring.

In other words, the appearance of a snake in the given area represents reproductive danger, not only danger in general. On the other hand, scientists analyze different reactions in response to the appearances of snakes. In particular, it is possible to claim that a snake in the vicinity of a bird's nest is likely to cause a mobbing behavior whereas observing the snake far away from the nest will have a different reaction from the birds.

The breeding season causes increased aggressiveness regarding defense of nests

The study of barn swallows, which was conducted in the Journal of Animal Behavior, proved that during the breeding season, birds mob much more than usual, especially with nestlings. For the birds, the investment is actively involved and needs protection because laying eggs and nurturing chicks takes several weeks, which makes losses of nests quite damaging biologically.

Ecological studies conducted recently and published on the website of PubMed in 2023 found out that snakes could be predators for the nests of birds, and they had a big impact on bird populations. Researchers believe that frequent attacks by snakes might have played a significant role in the evolution of the behavior concerning the defense of nests. It becomes quite clear that birds confront much bigger animals right there in front of their nests.

How birds gather other birds around their nests

One of the most interesting aspects of mobbing behavior is how quickly it happens. The first bird may spot the predator, but she will alert others. Japanese Tits, for instance, were shown to join a search for a predator after hearing the particular call made by the first bird. The whole mob then attacked the predator.

Mobbing works thanks to disorientation of the predator as he becomes surrounded by too many birds. Social learning might be used to promote the above mentioned method as well. It was found out in the journal of Biology Letters that young birds can be taught how to sense danger using other birds' alarm calls. This means that some species of birds were able to learn about some dangers even without experiencing it.

Why do some birds hiss like snakes?

Although birds are known to hiss when there is something that poses a danger to them, sometimes they mimic sounds of snakes as well. According to the study made in the Current Biology, some tit species produce hissing sounds resembling snake sounds. This made predators more careful around those areas because the presence of nests was suspected.

The reason why experts consider this behavior to be beneficial is that it causes confusion among predators and if they suspect that there is a dangerous creature in that place, they will never approach the nest.

Physical defense mechanisms against snakes

In addition to behavior, birds employ physical defenses as well. A comparative study of the weaverbirds and icterids showed that species making their nests as a hanging nest structure with elongated entrances might lower the threat posed by climbing predators like snakes.

Such a nest design will be more difficult for the predators to enter and take out eggs or chicks since it will require them to spend much time on this process. According to researchers, behavioral defenses and architectural designs always go hand in hand. For instance, alarm calls, mobbing, and proper nesting locations have high potential in ensuring the offspring's survival.

Why does this behavior happen in backyards

From a safe distance, mobbing behavior appears scary and threatening. However, experts believe that the situation is more related to nest protection than danger for humans. Birds perceive a predator who wants to kill their offspring. Calls, flying, and attacking in a crowd are survival tactics used since thousands of years of evolution.

The next time a bird swarms at a snake in the backyard among shrubs, trees, or nest boxes, mobbing behavior is most likely to indicate the arrival of breeding seasons.