Why are they here? I think it is because the tree is next to a lamp light on a brick stack. This is probably providing vital heat for a small bird at this time of year. The other reason why they gather in large numbers is because they communicate to each other. You can hear these black, white and grey, tail wagging birds calling in unison. "Chesick, chesick, chesick", the tree was full of noise. Eventually, the noise grew to silence and the event was over. The wagtails had gone to sleep. Another of Norwich's secret wildlife spectacles was finally revealed to me. It may not be a starling murmuration, but it was just as good.