On the Wild Side with Professor Ian Rotherham: Baby blackbirds assuming adult plumage

From midsummer onwards, the garden was full of baby birds some looking very different from their parents. I previously mentioned the pale plumaged of juvenile starlings looking unlike their parents and thus causing confusion in identification. However, the same thing happens with other species from blue tits and great tits to robins and goldfinches for example.

The reasons of course are twofold, one being to avoid antagonistic reactions from the adults. Give a baby robin a red breast and the adults will attack it and potentially fight to the death. Indeed, simply place a round, red-coloured object in a robin’s territory and it will probably trigger unmitigated violence.

The other reason is related, and this is to have features leading to a parental response particularly food provision. So, many baby birds have bright yellow around the corners of the beak that when opened appears as a distinctive ‘gape’, producing an almost irresistible urge on the part of the parent to stick food in it!

In some species there is more, and so a herring gull adult has a red spot on the bill that stimulates the youngsters to peck at it. This then makes the parent regurgitate a ‘ready meal’ of say warm, part-digested fish or some other exciting titbit.

This difference in plumage and markings between adult and juveniles changes as the youngsters mature and that varies from species to species, in part depending on life-expectancy. For a long-lived bird such as an eagle for instance, the development takes several years, whereas for a shorter-lived ‘passerine’ (generally the smaller songbirds) it may happen within a few months of fledging.

So, my baby blue tits and great tits have now mostly assumed full adult markings. Indeed, this process has been very noticeable in this year’s younger blackbirds. At least three successful broods have produced speckled, rather thrush-like babies, and by July the first of these were already taking on grown-up markings. The young males now have fully black bodies but distinctive russet-brown heads. The females are chocolate brown with speckling on the breast, head, and neck.

You can contact Professor Ian D. Rotherham, researcher, writer & broadcaster on wildlife & environmental issues, at [email protected] and you can follow him on Twitter at @IanThewildside and via Ian’s blog.