Animal of the Week July 5, 2017—a bird on the move

So many modern tales in natural history are about declines, extinction, and the damage humankind does to its environment. When animals do succeed, it's because people messed up the environment and to the detriment of other species: just think of all those island species wiped out by invading rats, cats, pigs, and mongooses...but this week's animal is one that bucks the trend.

Cattle egret, Cburnett CC

The cattle egret, Bubulus ibis, has undergone perhaps the most remarkable, impressive, and natural expansion of any animal. Originally found hanging around with herds of buffalo, wildebeest, and cattle in sub-Saharan Africa and India, in just a short while this small white heron has made its way west to the Americas, south and east to Australia and, recently, north as far as the UK, where at least one and perhaps several pairs are raising chicks right now.

Naturally vagrant and prone to wandering with or in search of herds of ruminants, having crossed the Atlantic under their own steam is no small feat—they arrived on the east coast of South America in the early 1900s and by the 1970s they were quite widespread across the southern half of the USA. They reached Australia in the 1940s, presumably spreading east and south through Asia; and by the 1960s they were resident in New Zealand.

Historically recorded in the Iberian peninsula, they recolonised that region in the early 20th century and began wandering further north. Increasing numbers became frequent visitors to the UK. The first recorded breeding took place here in 2008. In the winter just gone, up to 70 birds were recorded across the country and quite a few seem to have stuck around. Perhaps they will join the great white egrets and little egrets, which have recently established themselves as breeding birds in the UK.

The expansion might well have been facilitated by human activity—if not by direct transportation then by creation of large herds of cattle. The egrets specialise in gleaning insects and small vertebrates disturbed by grazing herds and picking off ticks and other nasties from the grazers themselves, and warming climate is likely a factor in their increasing presence in the UK. Nonetheless, they seemingly do little damage to other animals, filling a niche created by the herding of cattle on scale, they don't seem to compete with native herons being far less tied to the water.

With such an impressive colonisation of the globe, I, for one, welcome our new avian overlords.