Archivos de diario de noviembre 2017

17 de noviembre de 2017

Goliath Heron behaviour observed at Korsman Conservancy

Temporary Notice: Embedded videos of the Goliath behaviour are not presently displaying in this post, so please visit http://korsmanconservancy.com/goliath_observations.html to see the short videos. (October 2018)

In Autumn 2016, a young Goliath heron arrived at Korsman, a bird sanctuary in the middle of urban Benoni. Because of the increasing population of invasive Category 2 carp (everything has a silver lining!) Goli found plenty to eat and took up permanent residence.

Fishing techniques and eating the catch

Goliaths stalk fish leaning forward in open water or next to reed beds, where carp often lurk. They lunge for a fish, counterbalancing by drawing back their wings. Not every lunge is successful - Goli may miss or only partially 'spear' the fish. A successful catch harpoons the fish with his bill.


Goli takes the fish to the water's edge and lays it down, circling it and spearing it repeatedly until it is dead. On one occasion, a crowd of curious flamingos came over to see what was happening as Goli dispatched a thrashing fish.
Next Goli carries it around, frequently dropping it back into the water in the shallows, possibly to wash off mud, before positioning it correctly for swallowing. Goli can 'toss' medium sized fish directly into his bill, but bigger fish take several attempts to position and swallow. For the big ones, Goli stands with his head bent down to the ground for a full minute or two with the fish in its mouth, preparing for the big moment then lifts it up and gulps it down. The whole process takes about five minutes for a big fish.

After he swallows it, Goli lurches away off balance from his altered centre of gravity. He takes several sips of water and finds a spot to sit and digest for a couple of hours.

Food fails:

Goli doesn't eat every fish he catches. One fish was just too big and kept on slipping out of its bill. Goli also rejects seemingly suitable fish; he circles and pokes them then walks away without trying to swallow. (Later the fish disappear, probably scavenged by terrapins.)

When Goli caught a frog (Common platanna) although he shook and readjusted it until it looked like it would fly into bits, he just couldn't figure out how to position it to swallow. Eventually I had to give up watching and leave; I still wonder if it went down.

Goli's call

Goli has a harsh 4-5x bark, used in different situations. The first times I saw Goli call, it appeared random as he was still alone in the pan (before he found a mate). I once saw the bark used against Grey-headed gulls pestering it.

When the Golis were breeding, they would often call near the nest to signal to each other (and the chicks) that they were returning. I heard this exchange with a 13-week old juvenile in the nest:
Adult outside the nest: Kwaark
Juvenile: Wobbly and crackly Kwaark-kwaark-kwaark-kwaark-kwahark
Adult: Kwaark-kwaark-kwaark-kwaark-kwaark-kwark

The chicks 'chatter' a very fast repeated cha-cha-cha-cha-cha when hungry, heard when both in the nest and to the parents, even as late as 15 weeks old.

Delta wing and gular fluttering

Golis sometimes sit with their wings open in 'delta' position, often also gular (throat) fluttering (panting) for temperature regulation. Often seen in juveniles.

Flight

Goliaths have a wing span of two metres and their slow wing beats are distinctive.

Other things Goliaths do

They get itchy and scratch, they stretch, they visit high trees well above their normal habitat, and (as other birds do too) they lighten their load before flight....

Next instalment: Goli finds a mate

Ingresado el 17 de noviembre de 2017 por jane_trembath jane_trembath | 1 comentario | Deja un comentario

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