Cattle Egret in the Park

Written by Lucy Brzoska

An unusual visitor came to the park this week. While people lolled on the grass, kissing, reading and eating lunch, it quietly decimated the park’s lizard population.

Cattle egrets (Bubulcus ibis) breed in Barcelona zoo within the Grey heron colony. Unlike their bigger relatives, they are mainly land foragers and can usually be seen in the fields around the Llobregat Delta. Their adaptability to man-altered habitats is one of the reasons for the Cattle egret’s spectacular worldwide expansion over the last century (first pair bred in UK this year).

The opportunism of the egret in the park was richly rewarded. It stalked the ivy-covered ground, alert for rustling movements. Whenever potential prey was spotted, its neck would start wobbling. The undulation would travel back in waves, till even its tail was shaking. Its head, however, remained quite still. The sinuous movements seemed to be a way of warming up for the final pounce, which was nearly always successful.

The egret’s bill was an efficient pincer, applied with masterful technique. Each lizard was grabbed firmly by the body, away from the detachable tail. Sometimes the helpless lizards would wrap their tails around the egret’s bill, as if desperately trying to bind it. But struggling was useless. Inevitably they would be swallowed head-first, to join the ever-growing pile in the egret’s powerful digestive system.

On a short break, it stopped to preen, and caught a couple of flies, particularly annoying at this time of year. It was a reminder why Cattle egrets are valued by ranchers as an alternative to pesticides. They are often to be seen delicately picking bugs off animals’ backs. But the egret in the park soon went back to its more solid menu, swallowing reptile after reptile.

I began to worry about the park’s lizards, (mainly Podarcis hispanica), who normally enjoy a placid predator-free existence. But later I read about a study of an island population of lizards – the park is like an island in the city, after all – which involved unleashing an alien predator and observing the effect on the resident reptiles. The population was badly hit initially, but the species triumphed, exhibiting longer legs at first (better to run with) and then shorter legs (more useful when they took to the trees). An example of rapid evolutionary resilience.

The Cattle egret returned to hunting, but I’d had enough of observing. My lunch-break was nearly over, and I was starving.