Willow
Tit

They are the only British tit species that excavates a brand-new nest hole every single breeding season. The female uses her small bill to bore and chisel into soft, rotting tree stumps or dead wood.

All that heavy drilling and chiseling gives the willow tit a noticeably thick, "bull-necked" appearance compared to its sleeker look-alikes.

They look so much like marsh tits that ornithologists did not realize they were a separate, distinct species until 1897.