The Dunnock is similar in size to the House Sparrow, though it is a sleeker bird with a fine bill. The plumage is rather drab, being a mixture of grey on the head and chest and brown elsewhere. The upperparts and flank are streaked with warm-brown tones. Dunnocks are usually seen foraging on the ground, shuffling about ‘mouse-like’ in search of food, the tail moving nervously. Young birds have olive-brown eyes, these developing a stunning mahogany-red colour when the young birds reach their first Christmas.
Although some people still refer to the Dunnock as ‘Hedge Sparrow’, the Dunnock is no Sparrow. Instead it belongs to a family called the accentors. Originating in the Himalayas these are cover-loving insectivorous birds with sharp, pointed bills.
For many years a peculiar piece of Dunnock behaviour had been noted by many people – vent or cloacal pecking. One Dunnock was seen to peck under the tail of another but there was no explanation of what was happening. A few years ago Nick Davies, working in the Cambridge Botanical Garden, found out the absolutely stunning explanation for this behaviour.
Dunnock breeding behaviour has evolved into an amazing melange of systems, with monogamous pairs, pairs with two males and one female and even pairs with two males and two females. Many males were trying to father chicks with females in other territories, pecking at the female cloaca to displace any sperm from a previous mating before mating themselves. Cloaca pecking was all about the cock bird trying to ensure that he was going to fertilise as many eggs as possible.