I am right in thinking 'Alla' can also mean 'everyone'? If so, how do I distinguish between this meaning 'Everyone's birds died'?
"fåglarna" = "the birds"
If the sentence was "Every bird died.", I'd put "Varje fågel dog."
Check if I'm right: alla fåglar = all birds; alla fåglarna = all (of) the birds (e.g. those in the zoo) Is that correct?
No actually, 'strange' can be främmande in some cases (strange = not previously known, unfamiliar), but usually it's konstigt (strange = odd), and that's what it would have to be here. Livet är konstigt. Språket också.