Eurasian Oystercatchers are loud in volume and loud in plumage. There are no words for skulking, camouflage or whisper in the Oystercatcher’s vocabulary. They have a completely different method of maintaining themselves and prospering from the Eurasian Curlew with which they are sharing this buttercup field.
Oystercatchers are widespread birds. They occur in Western Europe as well as China and Korea. Across that huge distance they show an interesting feature; there’s a subtle change in their bill from west to east (or east to west depending upon your origin). Some Oystercatchers have broad-tipped bills and use them to prise open molluscs or hammer through the shell. while some have pointed-bills and dig up worms. Individual birds specialise in one technique or the other and they learn the feeding method from their parents.
There’s a change in the bill and in the feeding method across the Oystercatcher’s population. This kind of a geographical gradient of features is called a cline. It’s a bill cline.
If only it would stop shouting at me I would be able to think how cool that is.