"One of the most vulnerable species is likely to have nested on the Shiants in the past, and may do so again, but it's unlikely in the presence of rats. How much evidence do you need?"
Actually there appears to be no real evidence that Manx Shearwaters ever bred on the Shiants. Speculation yes...
Goodbye to the last colony of Black Rats in the UK based on zero evidence. Shameful waste of money.