Dogs and cats are able to see into the ultraviolet part of the electromagnetic spectrum. This allows the animals to see in wavelengths invisible to the human eye.  

A new study suggests house pets may be able to see intricate patterns on birds and flowers, which are invisible to people. However, seeing in ultraviolet wavelengths may not be an entirely good thing. This ability also gives cats and dogs the ability to see dried puddles of urine. This may aid the animals in marking territory, and recognizing property controlled by others. 

Up north, the ability could serve an additional purpose. Snow absorbs UV light, while white fur does not. This means prey, like winter hares, or predators such as polar bears, would look dark against the white backdrop. Reindeer also see their environment in ultraviolet light as well. This same ability is employed by other animals, such as hedgehogs, ferrets, bats and several other rodents. Many other animals, such as fish and birds, were known to see these wavelengths of light. This study was the first to show this ability exists in cats, dogs or rodents. 

"It was assumed that most mammals do not see UV because they have no visual pigment maximally sensitive in the UV and (instead possess) lenses like those of man, that prevent UV reaching the retina," Glen Jeffery, of the University College London, told Discovery News. 

The researchers found these receptors were not always required in order to see these wavelengths of light. In humans, ultraviolet light does not pass through our "ocular media," the clear parts of the eye like the cornea. What the study found was these structures in some species allow UV wavelengths to pass. Viewing the world in a wide range of light frequencies could also allow the animals better viewing in low-light conditions. 

Humans are able to see objects in great detail, compared to many animals. Seeing UV light in addition to other frequencies may create slightly fuzzy images, according to the study. This may be why this ability is not present in most people. A few people who have had their eye lenses surgically replaced can see into this part of the spectrum. 

A study profiling research into the ultraviolet vision of the animals was published in the Proceedings of the Royal Society B.

In addition to urine, other materials, largely unseen by humans, may be visible to pets. This includes chemicals used to brighten paper. A simple sheet from a notebook could seem fascinating to a cat. The next time you think your pet might be seeing something you're not, you may just be right!

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