Spotted Eagle-Owls in Johannesburg

Spotted Eagle-Owl, Bubo africanus, photographed in Johannesburg.

The Spotted Eagle-Owl, Bubo africanus, is one of the few raptor species that can be commonly seen in urban and suburban Johannesburg. Its mournful hooting is a delight to some suburbanites, though there are also those who believe the owl to be a bad omen. In 2012 many owls were released into a rat-infested area as part of a project aimed at descreasing the rodent population. The project was eventually scrapped due to these superstitious beliefs.[1] People killed the owls because they were afraid of them.[2] Another great killer of owls is their inadvertent poisoning through poisoned rodents. [3] Yet despite these challenges, the Spotted Eagle-Owl is still relatively common in Johannesburg and can be classified as successful.

Spotted Eagle-Owl, Bubo africanus, photographed in Yoeville, Johannesburg. Note the Grey Go-away Bird mobbing the owl. Image courtesy of Francis Burger. 

The horned tufts on the owl have been suggested to be an evolutionary adaption to aiding in the animals camouflage by breaking the owl’s outline. Another theory on the functional purpose of the 'horns' is that they aid in visual communication between owls.[4] There is also an interesting theory that was put forward by a Norwegian study of eagle-owls in Europe, which identifies the “ear tufts” as a mimicry of mammalian carnivores. [5] This theory ventures that the ear tufts mimic facial patterns of potential predators in Europe such as the lynx, fox and marten. “In ‘face to face’ encounters they suggest that a specialised aggressive facial expression on the part of the owl may cause it’s potential ‘look-alike’ predator to withdraw”. In an African context the same could apply for predators filling the niche of the owl's European predators: think about the Caracal, Jackal, Serval and any other mammalian predator of that size. Then consider how cat-like the owl's silhouette is when seen on a roof or wall at night.

The ear tufts on this Spotted Eagle-Owl may be a mimicry modeled on potential mammalian predators.

What I like about this theory is that it makes one think of owls as vulnerable to predation.  Thus the theory also fits seamlessly with the theory that the ear tufts evolved for camouflage. Another thing that these theories force one to think about is the evolutionary path that owls took. Many people assume that owls are 'more or less' nocturnal eagles and that they share a common ancestry with eagles and other Falconiformes. Owls actually share an ancestry with the cryptic and nocturnal order of Caprimulgiformes, which includes nightjars. 

Once one begins to think of owls in this way it becomes quite easy to imagine the journey taken by little, nocturnal, night-jar like birds, slowly changing into owls: the more upright stature to be camouflaged against tree trunks, the development of talons and a flesh tearing beak to consume larger and stronger prey, and then slowly the development of ear tufts and an increase in size to aid in camouflage and deter predators of the mammalian variety through an interesting tactic of mimicry that mirrors the potential predators. 

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[1] http://www.joburg.org.za/index.php?option=com_content&id=7846:owls-take-flight-in-alex&Itemid=192

[2] The owls were kept in a feeding box at a local high school for 21 days and released to hunt the rats. Bright idea, but the community killed the owls for superstitious reasons (http://www.sowetanlive.co.za/news/2013/04/18/all-they-need-in-alexandra-township-is-the-pied-piper-of-hamelin).

[3] Owls may be paralysed or killed after eating rodents poisoned by certain rodenticides. Poisoned rats and mice, whether dead or moving slowly as a result of being poisoned, are easier for owls to catch. Thus owls will eat more of these, and accumulate a large dose of poison (http://deltaenviro.org.za/resources/envirofacts/raptors.html).

[4] Carnaby, T. 2008. Beat about the Bush: Birds. Jacana Media: Johannesburg (pg 472-473).

[5] I was made aware of this theory in Peter Steyn’s book on owls. Steyn, P. 1984. A Delight of Owls: African Owls Observed. David Philip: Cape Town (pg 90).