Giants of the Nahoon River

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Giants of the Nahoon River

The Goliath Heron (ardea goliath) is a majestic bird. A pair have made themselves a nest on the Nahoon River island.
Peter King

If Goliath Herons could read, they may not be impressed. One authority describes their calls as being “similar to the raucous barks of an old dog”; another suggests their repertoire includes “croaks, squawks, growls and gurgles”. Wikipedia records the calls variously as kowoork, arrk, kroo and huh-huh – not as majestic as the African Fish Eagle, admittedly, but each presumably having its own intended meaning.

The Goliath Heron – the world’s largest by a fair margin – is one of at least six species of heron that call the Nahoon River home.

This extraordinary bird can attain a height of 1.5 metres, a mature mass of almost 5kg and a wingspan of more than two metres.
While the Goliath is similar in its slate-grey and chestnut colouration to its cousin the Purple Heron (Ardea purpurea, also a Nahoon resident), these exceptional dimensions make it easy to distinguish, being a full 70cm taller than the Purple and 50cm taller than its more distant relative, the Grey Heron (Ardea cinerea).

With the full bloom of summer now upon us, our resident pair of Goliaths has made themselves at home on the island in the upper tidal reaches of the Nahoon estuary, causing a flutter among the lucky few whose properties overlook the river, as well as a fair amount of interest in the twitching community.  

Not uncommonly among birds, the species is generally socially and sexually monogamous, while plumage does become brighter during the nesting season and a breeding “duet” has been reported. Kushlan and Hancock (2005)1 suggest that the absence of any distinct mating rituals may be due to the fact that the birds do not compete for new partners each year. It occurs to me that this may also explain why some humans are not inclined to dance!

Unsurprisingly due to their size, Goliath Herons have few natural predators, although they are vulnerable to “kleptoparasitism” – with African Fish Eagles having a particular penchant for stealing their prey before they have a chance to swallow it.

In India (where Goliaths also occur), the species in times past was considered a delicacy, reportedly with similar taste to the pheasant. However, hunting was restricted owing to its being classified as a “royal gamebird”, probably saving it from decimation on the sub-continent.  

Their own prey includes a wide variety, from carrion to fish – typically feeding only on larger prey in normal circumstances, while often scorning opportunities to eat smaller fish, reptiles or amphibians.

This has been dubbed a “jackpot” hunting strategy (the logic being that it pays dividends to ignore the small fry, in order to increase one’s prospects of a big score).

Studies of the feeding habits of Goliaths have shown that the average size of prey items measures approximately 30cm – quite a mouthful, which must be manoeuvred to go down head-first. This can be quite challenging if your breakfast is a young crocodile! Believe it or not, this happens and can be viewed on YouTube.

Goliaths are stealthy or “passive” hunters, often remaining practically motionless for long periods before coiling the neck and bayonetting their prey with their sharp bills.

Reasonably common in inland waters throughout sub-Saharan Africa, the Goliath is not considered endangered. Their size, however, militates against dense populations – meaning that it is unlikely that the Nahoon estuary would host more than one or two pairs simultaneously.
While the species is not migratory, environmental pressures (mainly inland) can trigger nomadic movement, with individuals having been recorded moving between 100 – 300km between seasons.

With facilities like the Nahoon Estuary Nature Reserve on our doorstep, as well as a wide variety of biomes within easy access of East Londoners, we are fortunate indeed to be able to enjoy a wide diversity of birding in a generally safe environment.

1.Kushlan & Hancock: THE HERONS, New York, OUP, 2005.
- Peter King

 

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