These elegant birds (altho the one of the right looks a bit grouchy) are Cattle Egrets. These birds (like many others) have been steadily extending their territory northward. (I suppose similar things have happened in the southern hemiphere, although less perhaps, since land masses are more separated there.)
My brother Simon snapped these Cattle Egrets in Bedfordshire.
Cattle Egrets are often seen in wildlife documentaries, usually perched on the back of cattle. They pick out and eat ticks and other pests, and it's a form of symbiosis. But round here they don't seem to do this; probably because there are relatively fewer cattle, and more other food opportunities, as seen in the photo.