The harsh sound of agitated birds can easily draw one’s attention out in the bush. Little birds will make a serious racket when a perceived threat is nearby. Threats come in many forms and shapes from snakes and large lizards, to mongooses (particularly in the case of ground-nesting birds), genets, baboons and even leopards. In fact, if you have ever been on a game drive out here you would know that when tracking a leopard, the harsh alarm calls of birds can generate great excitement as there is a good chance that the leopard is close by!
But why would a small bird such as a starling or a fork-tailed drongo risk its life by purposefully and aggressively flying towards, and sometimes making physical contact with a large raptor?
Let’s break this down a bit further – why do birds and animals alarm call in the first place? Alarm calls are a form of communication that is understood between species. They function to alert other individuals – including from other species – of the presence of a potential predator in the area. For example, the alarm call of a robin will also draw the attention of a starling, who then knows to be more on the lookout. Different species will even work together to drive a common threat out of an area. Alarm calls also serve to inform the predator that it has been seen. This will often cause the predator to give up on the hunt as the element of surprise is lost.
We recently spotted an African harrier-hawk perched on a dead tree; we had been made aware of its presence by a series of harsh, raspy alarm calls. A greater blue-eared starling had seen the harrier-hawk land on the dead tree and had begun to chirp harshly, flying back-and-forth towards the raptor, often turning away only at the last minute. This drew the attention of a larger Burchell’s starling, which came and joined in the mobbing. Starlings are never happy to have African harrier-hawks around as these birds of prey have evolved long legs that are extremely flexible, almost double-jointed. This enables them to raid nests of birds that utilise holes in trees, such as starlings.
But don’t the raptors turn on the mobbing birds as prey? Well, the smaller birds are normally a lot more agile; capable of making quick turns and evading capture. It can happen that they get caught though, thus often the attacks from the smaller birds will come from above when in flight to avoid the talons of the raptor they are mobbing, or from above and behind where a raptor is perched. Still rather risky business in my opinion!
Once a predator has been alarmed at, its cover has been blown thus the element of surprise is no longer an advantage. In most situations, the predator will then give up hunting in that area. This African harrier-hawk in this instance did give in to the constant harassment by the starlings and eventually flew away into a completely new area.
We thought that the harrier-hawk was leaving to find a new area to hunt. Upon closer inspection though, and only when writing this blog, did I realise that the harrier-hawk had infact already caught some prey – presumably a starling chick! This would explain why we witnessed one particular starling continue to mob by following the harrier-hawk very high up and for a long distance away from where it was initially perched!