Blackbird variation

Activity overview

Run the activity

1. Show the three images above and ask everyone to come up with as many similarities and differences as they can. If they get stuck, prompt them to think about:

• appearance
• what they do
• where they might be found

2. Then, everyone needs to decide which one is the odd one out and why. Encourage a reason for every answer and there is no wrong answer!

Background science

These birds are all blackbirds. We could identify them using their size and shape because blackbirds are one of the bigger songbirds in our gardens and parks. They have a distinctive yellow-orange beak and ‘eye ring’ (the iris surrounding the pupil). Confusingly, female blackbirds (shown in photo 1) are not completely black like the males (shown in photo 3) but have a dark-brown body with some streaking on their breast. The females of many bird species have a duller appearance than the males which is thought to provide camouflage when they are nesting. Juvenile (young) blackbirds are also a mottled, tawny-brown colour for the same reason.

Within a blackbird family, the offspring look similar but not exactly like their parents; they may be bigger, smaller or have slightly different coloured beaks. This is called natural variation and occurs whenever living things reproduce sexually. Natural variation can result in a beneficial trait. For example, a bird with a louder singing voice may attract lots of mates and produce more offspring. However, variation can also result in traits which make survival (and so reproduction) more difficult.

The middle photo shows a blackbird who has inherited a fault in their DNA. This is a leucistic Blackbird. Leucistic creatures have white patches which can cover most of their body. The white feathers have been produced in places where the bird cannot produce melanin. The colour of hair, eyes, skin, fur, scales and feathers in most animals and humans is controlled by the pigment melanin. Melanin is important for good eyesight and protects us from the sun. Sometimes a mutation (think of it like a spelling mistake) in an animal or human’s DNA completely stops melanin from being produced, resulting in white hair, feathers, scales or fur and red pupils. This trait is albinism.

Albino creatures differ from leucistic ones because they do not have melanin in their eyes (as well as their fur/feathers/skin). This results in the animal having extremely poor eyesight which makes it hard for them to survive. Being leucistic is a disadvantage for this blackbird because it causes weakness in the feathers and highlights the bird to predators. Scientists have found that there are more leucistic blackbirds in cities than in non-urban areas. Why might this be? Some scientists suggest that there could be more predators in the non-urban areas or poorer nutrition, but they need to do more research to confirm their ideas.

Take it further

Activities

Listen to the beautiful blackbird song and find out more about the species with the RSPB. Learn about how variation can work with natural selection to drive evolution by trying this Peppered Moth game.

Watch

This BBC video describes the natural variation in a litter of puppy guide dogs and this one investigates the traits of different dog breeds and selective breeding in plants and animals.

If you want to try more activities exploring camouflage, try If you see me now or  Mystery markings . Or to discuss variation in more depth, there is How much variation is there in how we look? Or What if all humans looked the same?