AFRICAN OPENBILL IRRUPTION – OPEN TO DEBATE

The African Openbill (Anastomus lamelligerus) irruption appears to be an ongoing affair with sightings progressing steadily westwards from KZN through Eastern Cape and now along the Atlantic seaboard north of Cape Town as I type.

What caused this unprecedented influx by this high gregarious, medium sized stork of aquatic habitat preference to vacate its known sites within tropical Africa for a deep south migratory flight is still something of a mystery at this stage.

Normally associated with wetlands, swamps, rice paddies, lake edges, large perennial rivers this unmistakable stork, with its highly specialized bill adapted for the skillful extraction of fresh water snails and mussels from their protective shells, is confined in the main to trans-equatorial movement in tropical regions.

Within this sphere of movement migratory behavior appears to be dictated by the availability and abundance of preferred food types and is closely linked to rainfall and breeding site selection.

Numbers within favoured feeding and breeding areas range from abundant to very abundant and the population as a whole appears to be stable and not under threat within its recorded range.

So why did a break away collective embark on a journey southwards to the Western Cape?

Could it possibly have had something to do with an aberration in the weather pattern associated with the intra-tropical convergence zone moving further south than normal and apparently settling in over Gauteng…

Or could it in some way be associated with an equally unexpected irruption of Namaqua Doves and Lark-like Buntings that arrived in number along the west coast in November in response to adverse conditions in the central interior.

Although the regular pattern of African Openbill migratory movement is not clearly understood it is known that the majority of birds breed slightly south of the equator in tropical areas close to their main food supply of fresh water mussels and snails.

So why the influx? Is it simply a case of a breakaway group of young radicals taking a gap year or a wayward flock of stragglers suffering from reverse migration and heading south and not north as is usual at this time of year.

Perhaps it was simply a ‘kettle’, an American birding term for hundreds if not thousands of birds, spiraling on thermals to gain altitude before gliding as a collective in a set direction that collapsed in a state of geographic confusion due to jet stream interference.

Maybe it was simply ‘pure wanderlust’ as so succinctly stated by Iain Sinclair on radio many years ago when asked what explanation was behind a mega ‘tick’ in the form of a Herring Gull finding its way all the way to Durban from Europe to the delight of the local ‘twitching’ community.

As of the time of writing reports of recent sightings are still coming through with the latest from Intaka Island on the northern outskirts of Cape Town.

Who knows whether the latest arrivals are the remnants of the original flock or an independent contingent of seriously lost birds soon to return from whence they came leaving the question as to what caused the unexpected irruption open for general and scientific debate…

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