Eagle Eye

Birds of prey can spot prey at great distances.

One of the most important human senses is sight, and we rely heavily on it. However, many bird species have even better eyesight than humans, especially birds of prey, such as eagles. For example, one species of eagle can see prey the size of a hen in the grass from a distance of about 6.5 km, something people can see from only about 1 km away.

1. Invite pupils to line up on a common starting line 35m from the board (use school hall).
2. Take the landscape poster from the toolbox  (or download below) with the squirrel hidden on it and hang it on the board (or project it).
3. Let students know that the starting line is the distance from which an eagle can spot the prey in the image. Gradually ask the pupils to more closer to the image until the first pupil can see the animal. Ask the pupil to name and describe the prey to ensure they are correct. Alternatively, without talking, as pupils to write the name of the animal on a slip of paper and place it face down in the place they first identified the animal.
4. Everyone can continue moving forward until they are able to recognize the hidden animal with their eyes.
5. Finally, measure the original distance from the picture and the distance from which the first student observed the outline. Ask students to count how many times it is shorter than 35m.

How come birds of prey can see so much better than humans?

Simple explanation

BIrds of prey have much greate visual acuity than we do. This means the sharpness of their vision is far better. This is not the same as magnification which just makes an object appear closer, but not in sharper focus. With this greater visual acuity, birds of prey can see details at up to ten times greater distance than we can.

More detailed explanation

It can be said that the eyes of birds of prey are not so different from ours, but in almost all necessary parts they are superior to ours. For example, the relative size of the eye is very important for the quality of vision, the bigger the better, because it allows in much more light. If our eyes were are large as birds of prey in relation to our head, one of our eyes would weigh 750g and not 7.5g as it really weighs.

Another essential factor in the quality of vision is due to specialized cells called photoreceptors located inside the eye. These capture the observed image and send signals to the brain. For example, there are about 160,000 photoreceptors per square millimeter in the place of the densest swelling, the so-called yellow spot of the human eye; in buzzards it is over a million. Moreover, these photoreceptors are distributed over a much larger area than humans. Imagine a cell phone with only a few pixels - that's a human compared to a bird of prey.

These things are among the main (but not the only) reasons why eagle eyes are so much better than ours.

Knowing the principles by which the properties of bird's eyes are improved can lead to a number of applications. Can you think of some examples where this could be used?

Inspiration from the sight of birds of prey is currently being used, for example, in safer car sensors, better detection of phenomena on Earth from space (satellites) and astronomical phenomena (e.g. asteroid detection).

Some STEAM opportunities include:

• Recognise that light appears to travel in straight lines, and use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye.
• Explain that we see things because light travels from light sources to our eyes or from light sources to objects and then to our eyes.
• Describe how human eyes work to collect light.
• Observing and raising questions about how different animals adapt.
• Analyse advantage and disadvantage of different adaptations/behaviours.

In a number of languages, ​​we find an idiom referring referring to the quality of sight of birds of prey. Can you name any?

e.g. eagle eyed (English + many others), falcon eye (Czech), vulture (Romanian), falcon (Polish), hawk (Chinese).

Some species (such as the kestrel) can also see in the UV spectrum (invisible to the human eye). Can you think of any examples of when this might be useful for them?  (e.g. seeing the traces of rodent urine to help find them)