Despite being fantastic animals with an essential function in the right environment, hedgehogs are not a native species to Colonsay and Oronsay. By Scottish law they should remain that way. No new information on how the creature ended up at Kiloran has come to light.
The introduction of hedgehogs has had severe consequences on other West coast islands. Hedgehogs are ground predators for many ground nesting birds such as lapwing, dunlin and redshank. These birds have suffered declines due to egg predation by introduced hedgehogs.
There are huge environmental and financial costs involved in the control and translocation of introduced animals. And these projects take many years to be effective.
Introduction of non-native species can be a serious problem. SNH provide guidance and outline the associated laws. To summarise: “The new legislation makes it an offence to release animals or to plant plants in the wild outwith their native range, whether intentionally or otherwise. The clear message is – if in doubt, don’t release and don’t plant.” This includes artificially moving locally native wildlife (like hedgehogs) to parts of the UK  that are not their native range e.g. offshore islands (no matter how long ago the move was made).
Find out more about identifying and recording non-native species on the SNH website and about what you can do about such sightings.
Information from the website of SNH (Scotish Natural Heritage); Info about introducing non-native species, provides details about the law in these situations.
Sources: http://www.snh.gov.uk/docs/B1113471.pdf
 http://www.snh.gov.uk/land-and-sea/managing-wildlife/uist-wader-research/aims-of-the-project/