Answer:
No the relation is not a function
Explanation:
A function by definition will have a unique output for every input, so there should be no repeating outputs, however, the clinic cares for 2 legged animals (birds) as well as 4 legged animals (cats and dogs). With this being said, if a clinic has 2 animals(input), the amount of legs(output) could be 8 if two dogs, or it could be 4 if two birds, or even six if a dog and bird.
If this were a function, the clinic would undeniably have different amounts of legs having two animals opposed to one animal, but this isn't true. if the clinic has 2 birds(input), there'd be 4 legs(output). but the clinic would also have 4 legs(output) if it had 1 dog(input). the output is the same for two different inputs
This shows the output is varying depending on the type of animal since the amount of legs changes, rather than the amount of animals.
Hope this helps :)