Cohabiting

I was all set to blip a pair of singing reindeer that Mum and I saw at a garden centre this morning, until I passed the egrets in the horse field on my way home. The reindeer, Holly and Dec, were doing an excellent rendition of Fairytale of New York, among other classics. I'm sure they were there last year as well, but not singing. Perhaps they've been building up their part? Anyway, back to the egrets. I counted at least 18 of them this morning and they were happily mingling with the Gypsy Cobs, and occasionally getting on their nerves. There are some more photos of them in Extras (along with the reindeer). What I want to know is, how come the horses get so muddy while the egrets say perfectly clean?