“Grey Herons (Ardea cinerea) are large birds. Naturally, not many predators are capable of handling their large size; especially with their spear-like beaks, which can double as formidable weapons. On the other hand, their eggs and young, being much smaller, are defenseless, and vulnerable to predation. Hence, for defense against predators, Grey Herons will jealously guard their nests, 24 hours a day. There will always be a parent in the nest taking care of the eggs or chicks.
“One predator that all nesting birds will have to be wary of is the House Crow (Corvus splendens). They are nest raiders and predators of eggs and chicks. Crows are opportunists, and may harass the nesting birds out of their nests to give other crows opportunities to steal eggs or catch the chicks. In the heronry, a crow was observed perching openly and boldly within striking distance of a nest (above left). The incubating heron remained in its nest, protecting the eggs as it sat on them. It was wise enough to ignore the crow so as not to expose its eggs. Fortunately for this incubating heron, it did not need to be concerned for long as its mate arrived shortly to chase the predator away (above right).
On another occasion, a Brahminy Kite (Haliastur indus) was circling in the sky above the heronry. It descended, and was scanning the area as it turned its head to glance around from time to time. Soon, the predator was soaring just metres higher than the tallest tree in the heronry (above left). At this crucial moment, a House Crow emerged out of hiding to chase after the kite (above right). Shortly after, another crow was seen joining in the aerial pursuit. The kite was obviously not ready to do battle as it flapped its wings to fly higher, getting away from the mobbing crows. After chasing the kite for some distance, the crows returned to perch in the heronry. It was puzzling that the nesting herons did not seem to react. There were no alarm calls, no evasive action, and none of the herons took flight. I could be wrong as my attention was mostly on the kite and my view was limited to only a few of the nests. However, for the few nests that were within sight, not a single heron was flushed out from their nests.
The crows could be protecting their own turf when they mobbed and chased off the Brahminy Kite.
Kwong Wai Chong
17th December 2010