“On 26th March 2014, I was admiring the diversity and behaviour of shorebirds along a mudflat in Singapore. These avifauna included Whimbrels (Numenius phaeopus), Little Egrets (Egretta garzetta) and Grey Herons (Ardea cinerea), all anticipating the retreat of the tide (above).
“A few juvenile Grey Herons were wading aimlessly and sheepishly along the shallow waters and one was repeatedly striking at a propagule of a mangrove tree (Rhizophora sp.) (above). It would pick up this green ‘toy’, let it go and retrieve it again, apparently enjoying its self-invented ‘game’.
“Sometimes, a broad dead leaf may also become the focus of such ‘playful fun’ (above). This reminded me of how curious toddlers love to put everything into their mouth and perform test-bites. Curiosity aside, repeated striking at inedible objects by juvenile Grey Herons would certainly provide much needed practice before qualifying as a skillful fish predator.
“While the juveniles were entertaining themselves near the shore, the adults were engaged in some serious fishing in deeper waters. One of them had just returned with a good-sized Eel-tailed Catfish (Plotosus sp.) in its beak (above).
“The heron handled the catfish with extreme care and caution, making a conscious effort to avoid the stiff spines on its dorsal and pectoral fins (above).
“Eel-tailed Catfish are recognised and respected as venomous fishes with stings that can cause intense pain, swelling, numbness, edema, gangrene, fever, weakness, nausea, local paralysis and dizziness (Auddy et al., 1995; Fahim et al., 1996). In addition, toxins have also been found in the skin secretions of such catfish (Shiomi et al., 1988).
“With this awareness of how risky and unpalatable it can be to manipulate and swallow an Eel-tailed Catfish, we can better understand why the heron was not in a rush to ingest its prey. So this determined and experienced heron brought the fish to the shallows and slowly brushed the prey’s body against the sand (above). Thereafter, it would dip the fish in and out of the water, as if to wash and rinse it. These actions would probably have served to remove the noxious slime from its skin.
“Finally, when the heron was convinced that the catfish was safe to swallow, it did so with little hesitation, head-first (above).
“This demonstrated finesse in the successful procurement and processing of a potentially lethal meal by an adult Grey Heron truly separates the ‘men from the boys’ and it would be a matter of time and lots more practice before the young amateurs graduate to become professional predators, just like their parents.”
Dr. Leong Tzi Ming
13th April 2014
1. Auddy, B., D. C. Muhuri, M. I. Alam & A. Gomes, 1995. A lethal protein toxin (Toxin-PC) from the Indian Catfish (Plotosus canius, Hamilton) venom. Natural Toxins, 3(5): 363–368.
2. Fahim, F. A., E. A. Mady, S. M. Ahmed & M. A. Zaki, 1996. Biochemical studies on the effect of Plotosus lineatus crude venom (in vivo) and its effects on EAC-cells (in vitro). Advances in Experimental Medicine and Biology, 391: 343–355.
3. Shiomi, K., M. Takamiya, H. Yamanaka, T. Kikuchi & Y. Suzuki, 1988. Toxins in the skin secretion of the oriental catfish (Plotosus lineatus): immunological properties and immunocytochemical identification of producing cells. Toxicon, 26(4): 353–361.