“On the morning of 23rd March 2011, the Pacific Reef Egret (Egretta sacra) was fishing for breakfast during low tide at its regular haunt along the Telok Kurau Canal. It occasionally employed light, foot-tapping techniques, targeted at submerged leaves, and succeeded in catching a few snack-sized fishes that would only have served as an appetizer.
“As it sensed the turn of the tide, it then took wing and flew downstream to where the water was slightly deeper (ca. 20–30cm depth), then stood absolutely still for a quiet period, watching and waiting for the first few fishes to swim up with the first influx of advancing waters. Then just as I blinked my eye for a split second, I realized that it had made a successful strike at a Crescent Perch (Terapon jarbua, Family Terapontidae), a common inhabitant of coastal and inter-tidal waters (above).
“This Crescent Perch actually proved to be a challenge for the egret to subdue and swallow, as it struggled vigorously, with dorsal spines fully erect, and its body constantly arched to a horseshoe shape (above left). Despite the desperate and determined attempts by the Crescent Perch to escape, the egret managed to maintain a secure grip of its prey, while manipulating the fish with its bill to find the optimum ingestion approach. Finally, the egret proceeded to ‘bite the bullet’ and simply attempted to swallow the Crescent Perch in its rigid, arched posture. This was a visibly uncomfortable exercise, as the bulge of the bent fish could be clearly traced as it crawled painfully down the egret’s throat (above right).
“Within minutes of ingesting the Crescent Perch, the egret had captured yet another fish prey. This time, it was a juvenile Sagor Catfish (Hexanematichthys sagor, Family Ariidae), an Australasian species living in coastal to estuarine habitats (above left). This catfish was not as tenacious as the Crescent Perch and might have shortly succumbed to the forceful strike upon capture. However, the egret was initially hesitant to swallow the catfish, and even carefully placed its lifeless body back into the water. At this point, my immediate hypothesis was that the egret may have had a previous traumatic experience with catfish, as many of them are armed with poisonous dorsal and pectoral spines. However, I soon learnt that my assumption was wrong. In fact, the egret was simply pausing to regurgitate the Crescent Perch (above right), then re-swallow it properly to avoid obstruction and discomfort in its oesophagus or stomach. Thereafter, it calmly picked up the catfish from where it left off, then silently, smoothly and swiftly swallowed the slimy prey.”
“I am grateful to Dr. Ng Heok Hee (National University of Singapore) for kindly and reliably identifying the catfish prey.”
Dr Leong Tzi Ming
24th March 2011