Many species of birds exhibit ‘mobbing’ tendencies, especially when they find predator birds resting alone or in small groups. Even those that are predominantly scavengers or fish-eaters are similarly mobbed. Such harassing behaviour is aimed at driving the predators off and in most cases they succeed. Mobbing is more pronounced if there is nesting involved, especially if eggs or young are present.
It is a common sight around Singapore to watch House Crows (Corvus splendens) flying after and driving off resident and migratory raptors of any species. I have personally seen Black-shouldered Kite (Elanus caeruleus), Brahminy Kite (Haliastur indus), White-bellied Fish-Eagle (Haliaeetus leucogaster), Oriental Honey-Buzzard (Pernis ptilorhyncus), Changeable Hawk-eagle (Spizaetus cirrhatus) and many other species being mobbed. House Crows do this individually or in a group, within and above their territories. Dr Wu Eu Heng has also reported seeing House Crows mobbing a Changeable Hawk-eagle around Jurong. Other bird species such as Black-naped Oriole (Oriolus chinensis) and Dollarbird (Eurystomus orientalis) also mob raptors in flight.
At many nature areas, particularly wooded areas, you often come across a party of highly agitated birds noisily moving around a tree or bush. Usually, this indicates the presence of a predator. In most cases this would either be an owl or a snake and the birds will both mob and scold in an aggressive manner. Greater Racket-tailed Drongo (Dicrurus paradisus) and Striped Tit-babblers (Macronus gularis) are often involved in such behaviour in the local forests.
Mobbing birds may comprise one or more species. It is a great opportunity to not only observe the irritated flock but to discover an usually illusive predator. I have seen some great snakes and owls in this manner. For example, the first Barred Eagle Owl (Bubo sumatranus) that I encountered in Malaysia was one that was being mobbed by a few bird species, including the Asian Fairy-Bluebird (Irena puella).
I am sure many birders would have encountered instances of mobbing and we would love to read about some of their accounts.
R Subaraj & Dr Wu Eu Heng
16th December 2005