"Han hører sin fugl."
Translation:He hears his bird.
I have a Danish book that says hans means his; are sin and hans both used to mean his; and if so what is the difference?
Yes, hans does mean 'his', but when you want to imply that it's 'his own' - you use sin/sit/sine.
He listened to his (someone else's) lecture - would use hans in Danish.
He listened to his (own) music - would use sin/sit/sine in Danish.
In English you can not say: He is hearing his bird. Always say:He is listening to his bird
Though it has a different meaning, "He hears/is hearing his bird" is a valid sentence.
You might see 'He hears his bird [...in the background],' but hearing his bird would be a rare construction - it's very strained. There again, it is incorrect to say 'I am loving it' but that hasn't stopped it's popularity in recent years.