What is it?

Went for a walk around Calke Abbey grounds, lovely day bit muddy underfoot. The paths close to the house were busy but the further away got the quieter it was. Stopped by the noise of as bird and stood watching it for ages, mostly running along a branch. Managed to get a few shots but have no idea what it is.
Finished the Agatha Christie book, really enjoyed it. Now starting Landlines by Raynor Winn. I read her first book and to be honest thought a lot of it was fiction, but she gets lots of positive reviews and now a film has been made I thought I would revisit her.
Hetty seemed to really enjoy the walk as she met lots of other dogs, including in the coffee shop where every table in the area we were in had at least one dog.
The album today was Robbie Williams Better Man, I really enjoyed it.