You are looking for the name of a bird that has gone from Monmouthshire. This will need a bit of research, and I hope you can find the right sources. You don't need to refer to The Birds of Gwent, and even if you did you would only get part of the answer.
This bird was apparently common in the county's uplands in the 19th century and persisted in the Black Mountains until the mid 20th century. There were a few sightings of single individuals in the 1970s, with the last in 1977. It is now almost extinct in Wales.
Once you have worked out what the bird is, you need to put its names into the checker to get the cache coordinates. Input them as capitals, with no spaces, in this order: colloquial name (1 word), english name (2 words), scientific name (2 words).
You can validate your puzzle solution with certitude.