Is the population of the Jay in decline in England and what threat do they pose to wildlife.

Jays are nest predators in the breeding season but they have co-existed with their prey for millennia in standard predator / prey relationships. Shooting Jays requires a licence so, unless this person held a licence, they have broken the law. Unfortunately, many of those involved in the shooting industry seem to think the law only applies to them if they get caught! Jay populations are designated Green (best possible) status in the UK and of least concern throughout Europe - but they have always been persecuted by humans.

Jays are virtually zero threat to grouse: for one thing Jays are predominantly woodland birds and grouse are predominantly mountain and moorland birds: it is not too often that their paths will cross. Interesting that he is "trying to breed a population of British grouse". Red Grouse are a native wild species. They don't need human help to breed. The only reasons humans want to "help them breed" is so that they can exceed the carrying capacity of the local environment, so there are many thousands of them to be killed in the autumn. It brings in big bucks for the landowners - and throws the odd bone to a few country folk (but not those of us who live in the countryside and love nature, not slaughter - which is a surprisingly large proportion - definitely a majority). This is the driving force behind the criminal persecution of protected birds and mammals on and around shooting estates, and the reason the RSPB has called for licensing of these estates, and why others have called for a complete ban on large bag driven shoots.