Kestrels, like many species of birds, are ablle to see UV light. Rodents have regular paths they travel and in doing so they leave urine trails along their favourite routes.

Kestrels have the ability to see these urine trails. This is a significant disadvantage for the rodents as Kestrels can follow these trails that are lit up like a map by UV light.

They are able to follow these lines, making it far easier to find their prey. The kestrels can then hover over these routes waiting for their prey to appear.