While out walking my dog I could see this pair heading down the canal.
When they spotted us they made a change of course straight for us. The coloured bird is the male and the brown one is the female. they are very common to see where I live. I did not know this but when looking up the birds latin name, I learned that only the females make the quaking sound.
They got quite close and I have a sneaky suspicion they were hoping we would have some bread with us, as the local children tend to feed them.