Nesting Grey Herons: 7. Feeding ritual

“The young of Grey Herons (Ardea cinerea) is usually fed by both parents with regurgitated food. The actual feeding proved difficult to observe when the chicks were small. However, as they grew larger, dramatic displays of their feeding behaviour could be observed. These feeding rituals could be quite a sight to behold.

“The chicks were quite sensitive to the presence of adult herons. When the chicks sensed the return of their parents, their crests will be raised in excitement and they will typically start their begging calls that sounded like bills clapping. After landing in the nest, the feeding ritual begins with the adult heron pointing its bill to the sky. Its crest will be raised and its bill closed. The food is nowhere to be seen as it has been swallowed and stored in the crop. The chicks will raise their heads to look at the adult, waiting in anticipation (above left).

“After a short moment of waiting, the chicks will start to grab at the adult’s bill with their large gaping bills (above right). They will tug and pull at the adult’s bill, sometimes very vigorously. This may happen a few times and the force will result in their heads being lowered towards the base of the nest. Their heads will be moving up and down aggressively and in tandem with the grappling of bills. The sharp end of their bills will sometimes poke into each other. Seemed highly risky; although no mishaps were witnessed. There may be a short reprieve for the adult, which will then point its bill skywards again. Sometimes, there may be a bizarre display of gaping by the adult, with its sharp pointed tongue exposed and the skin below its lower mandible and throat expanded (below). This did not always happen, but could be a sign prior to regurgitation. After more bill grappling, the regurgitation will be completed when the fish appeared in the adult’s bill; usually when their heads are low in the nest. The regurgitated fish will be quickly snatched away from the bill by one of the chicks.

“So far, only fish was observed to be regurgitated out of adult herons in this heronry. As most of us are aware, for ease of swallowing and to prevent the sharp spines of fish from damaging the oesophagus, fish will usually be swallowed head-first. How will the fish be regurgitated out of the throat? Head-first or tail-first? From a few of the numerous images that were captured during feeding episodes, the head of the regurgitated fish could be seen pointing towards the heron’s throat (below left).

“Thus, the regurgitated fish was in the same position that it was when swallowed! I find it amazing that the fish would be regurgitated out of the heron’s throat tail-first. There is a higher chance of injury caused by moving the fish in such a direction in the heron’s throat.

“Another interesting point that was discovered in the captured images was that there may be more than one fish regurgitated out during each feeding session. As shown in the image, although this could not be clearly seen due to partial blockage of view, both chicks could be seen with fish in their bills as circled in red (above right).

“The feeding ritual ends very quickly. Usually, each feeding session lasted less than a minute. After fulfilling its duty of feeding the chicks, the adult will repeat the posture of pointing its bill skywards. It was indeed showing itself to be a proud parent. Finally, the adult will fly off to seek more food; leaving the chicks, which quickly resumed to their resting state in the nest.”

Kwong Wai Chong
18th February 2011

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