Cattle Egret in the Park

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.

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Herons and Pelicans

The breeding season over for another year, by the end of August most herons have dispersed – though some will roost in the zoo during the winter. I found the plane trees deserted, with nursery activity reduced to the pines overlooking the pelicans, where young Cattle and Little egrets were still being fed. A handful of recently fledged herons also remained.

One grew tired of throat-wobbling and yakking, and crash-landed through the branches into the flamingo enclosure. The lion pen, fortunately, is quite far away. Dark and dishevelled, as if it had come through a chimney, it explored the area, not entirely sure where it was going. A more mature juvenile, sleek in morning suit-grey, exhibited the next stage of plumage in young herons.

The keeper arrived with a container of live goldfish, which he freed into the pelicans’ moat. It’s one way of stirring the hefty birds into action. They enthusiastically set about catching their lunch, casting their expandable bills sideways under water, like fishing nets. And there was plenty left for egrets and herons to practice their fishing skills too, deploying quite different strategies: the egrets would run after their prey, poised to change direction in an instant, while the herons relied on their long sinuous necks to snatch the fleeing fish. Owners of ornamental garden ponds would have had to look away.

As they live directly underneath the heronry, and share a fish diet, the pelicans are the captives most affected by its spectacular expansion. But although their placid existence has been disrupted, this year a pelican chick was successfully hatched, a rare occurrence in the zoo.

The one-footed Malibu stork that used to share the enclosure was immediately transferred elsewhere. A tough, powerfully-billed old warrior, it would brazen it out with the herons at their most competitive, while the pelicans, overwhelmed, huddled in a corner.

The baby pelican has grown into a vast fleecy lump that spends its life on a pedestal, being fed by doting parents. It appeared quite capable of looking after itself, lunging at one of the herons when it came too near. The startled heron waited till the chick had dozed off before approaching again, seeking out any forgotten fish.

Pelicans, herons and egrets, all were in moult, with feathers sticking out at odd angles, waiting to fall. The pelicans were like shabby old eiderdowns, shedding clouds of feathers. The plane tree leaves were also drifting down, and soon the empty nests will be visible again.

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