College Lake, Tring
I'm in the planning stages of a project to refurbish a bird hide to include artwork relevant to the Wildlife Sanctuary at College Lake.
Listening to bird song led to thinking about how birds see, and how their vision differs from ours. We have 3 cones in the retina: red, green and blue, which allow us to distinguish one million different colours. Most birds have 4 cones: red, green, blue plus ultraviolet, which means they can distinguish 100 million different colours - these birds are tetrachromats. Pigeons are believed to be petrachromats, they see an even greater range of colour.
Bees can also see the shorter light waves in the near ultraviolet spectrum, but they cannot see red, at the other end of our band of visible light. So to bees the colour red appears black, whilst they are very attracted to blue/purples.
What does this mean? It's hard for us to imagine exactly what birds and insects see, because our imagination is limited by our experience. Colour is not an absolute - it varies depending upon who is observing it. The impression of colour is given by our brain's reaction to the different length light waves. So we can never truly know what others see. Taking photographs with a UV sensitive camera results in images that are coloured by the filters that the photographer chooses to use.
What is clear is that birds and insects see different patterns of colour in ordinary objects, eg flowers, that are hidden to us, and they see these in addition to the colours we perceive.
Here are some images of flowers and bird plummage that give an interpretation of uv markings...