I keep 3 males and 2 females and I was thinking about getting more tomorrow
but when I came back from work this afternoon I found only 2 of my males left
1 of the males has some of its fethers missing
Sounds like some kind of predation.
Yup, second that. If you are not completely certain the cage is 110 % predator-proof, it probably isn't. Depending on what predators you have where you live, it can be anything from cats to snakes, rats, raccoons and lizards.
we live in Scotland
Are there any English around? I'd suspect them...
Otherwise it could be weasels, or is that the same as English? Otherwise cats, snakes or raccoons, though I don't know if you guys have the last two.
I would be way too wary of having buttons outside. Mine are inside. They are so tiny and flighty. If they are all together they could have attacked each other, buttons are very territorial.