Bird Buddy Blog

Why birds mob other birds – is it dangerous?

Courtesy of Geograph

Have you ever seen smaller birds fly at another, usually much bigger, bird? This is a calculated risk that birds will take to fend off the scariest of birds. We take a look at this seemingly foolhardy practice of taking on the big guys.

Sometimes on a sunny, blue-sky day, over the still air you may hear a buzzard call out its single piercing “keeeee!”. You look up, often into the sun, and eventually you finally locate the slowly circling silhouette above. Suddenly, you see two smaller flapping objects hone in on the buzzard, and then they’re flying all around it, seeming to land on it sometimes, and, inexplicably, the larger bird doesn’t attack its assailants. Instead, it seems to panic-fly away, desperate to make space between itself and them, calling and calling as it recedes into the distance, often pursued for a little longer.

Fools rush in?

It may come across at first as being a bit reckless, as if the little birds got sick of being looked down on all the time, started whining about it to each other, knocked back a few Wild Turkeys and decided it was high time someone showed that buzzard Who Da Man. But this tactic is far from some anthropomorphic fantasy of the underdog winning the day. This, as Tennyson lamented in his elegy to his friend Arthur Henry Hallam, is “Nature, red in tooth and claw”.

This apparent kamikaze behaviour of the smaller birds is in fact not a suicide mission, but a common defence tactic, or anti-predator adaptation, known as mobbing. in which the attacking smaller birds come out triumphant and live to fight another day.

Anti-predator adaptations are mechanisms that have developed evolutionally by those destined to be preyed upon, to help them in their endless struggle against being eaten by predators. Tactics can range from simply staying out of sight like bats flying at night, or nocturnality, avoiding detection by mimicry, like leaf insects, disruptive coloration, like chameleons, or even playing dead, like the possum.

This apparent kamikaze behaviour of the smaller birds is in fact not a suicide mission

Courtesy of Wikimedia Commons

Mobbing is an example of communal defence behaviour, and as the name suggests, relies on grouping together, often to attack a predator, rather than be passive victims of fate. Birds are not the only species who mob – meerkats, fish and bovines all use this strategy to protect what’s theirs.

Birds will mob anything that presents itself as a danger to their kind

Mobbing is a learned behaviour passed among species, but it can even be taught to birds by us. An experiment carried out in 1978 found that when a recording of mobbing blackbirds was played to fledglings of the same species who had been raised in captivity, they soon got the idea from listening to the calls, and tried to mob a plastic bottle.

Birds will mob anything that presents itself as a danger to their kind, not just other birds. Cats, snakes, foxes – even us, humans. Ever strolled along the seafront just enjoying your day then suddenly the air is filled with white wings and yellow beaks? It’s likely you’re being mobbed by gulls as you’ve probably wandered too close to a nest. Similarly, non-predators like herons or cranes are also mobbed, and it is thought that their large size or silhouette has them mistaken for a bird of prey.

Courtesy of Wikimedia Commons

Won’t someone think of the children

Birds will attack other birds for a few reasons, but the main reason for this behaviour, and the most frequent time of the year you will see this happening, is breeding season. Put simply, the small birds are trying to stop the big birds from eating their kids. Mobbing can come in the form of noise, and doesn’t always involve dive-bombing. If enough birds make enough noise, the would-be predator will leave the area with the knowledge that it’s been rumbled, and hanging around will likely result in a larger number of birds then taking the steps to attack it. Swallows are prime examples of noise mobbing – humans are frequently subject to this, as swallows tend to nest on man-made structures. Once chicks have fledged, if someone gets too close, the parents, ever nearby, will emit a very loud and unmistakable warning sound of single note PEEPing, which is not just telling you to get away but also telling any other swallows nearby what’s going on and to get over here: if you don’t vacate as requested, you will soon find yourself in the middle of a swallow typhoon.

But how about when the hawk has a nest in a highly crow-populated area, what happens then? Bird researchers have reported that, like their prey, predators will of course protect their nests as well, but crows seem to sense this, and adhere to a kind of no-fly zone in the vicinity. There does seem to be a case for imagining some sort of grudging respect there.

Police escort

I was once just gazing out of the window and watching songbirds quietly fuss around the feeders, when, in a flurry of chirps and short calls, they all vanished into the foliage. A sparrowhawk then alighted on top of a hedge nearby, looked around for a few seconds, and then it too suddenly started to alarm-call, then took off. In the same second, it was joined by two screeching magpies, who positioned themselves a feather-length away on either side, and physically escorted the sparrowhawk from the premises, out of my view. Shortly after, the songbirds returned to the feeders, and all was peaceful feeding diligence once more.

So, why doesn’t the mobbed bird fight back?

Mobbing is one of the rare times when different species will join forces to protect each other from a shared threat. Sparrows will regularly join in with crows and ravens to pursue a raptor, and starlings and blackbirds will do the same to crows. Some birds will even throw in a few bonus tactics such as defecating or even vomiting on the predator. When facing this kind of onslaught, is it any wonder why the animal under attack tries to flee?

Why do birds put up with it?

Even though the larger bird is often struck by the smaller birds during mobbing, it is rarely harmed. The smaller birds by definition lack the lethal elements of a hawk, who have talons and hooked beaks. So, why doesn’t the mobbed bird fight back, when it clearly can? As with noise mobbing, why does the predator just leave?

It’s all down to energy expenditure. The predator is already hungry, hence being there in the first place. It knows it has to find food, and frankly, there is hardly a choice to be made if it means spending half an hour exhausting itself fighting off crazed parents or just flying away and trying again somewhere else or later. The smaller birds may not have the weaponry, but they have the advantage of speed and manoeuvrability. With the greater numbers tactic also employed, it’s simply just too much effort to try and catch one, let alone all of them. Crows are of course larger than sparrows and swallows, and surely easier to catch, but crows are exceptional aeronauts. It’s just not worth it.  

Mobbing doesn’t always involve protecting the young and vulnerable, however. Food sources are protected by mobbing animals, and it is also used as a distraction technique, again with food, whereby the majority will target the individual in question, whilst one or two other members of the group sneak in when they’re not looking and make off with whatever was worth so much coordination and community, and share it later.

Working together against a common enemy – what nobler cause is there?