In Kingdom Come: Deliverance, you will get the side quest A Bird in the Hand from the huntsman in Rattay. He is in the north of the town and confesses that he should take care of his friend's three birds, but they have escaped him. Now you want to take the challenge and want to capture them for the huntsman. He will not only give you three cages to catch them but also teach you how the Nightingales (birds) sound. You will simply recognize it when you are near them!
If you unlock the quest, you see that the area where you are to look for the Nightingales is huge and also, there is a bandit camp in the woods that you should reach only if you have appropriate armor and weapons. If you approach a bird, the croaking will be hard to ignore. The following map shows you the exact locations of the nightingale birds, marked with B, C and D.
In the area of these locations, you open your inventory and select the bird traps and let them simply fall to the ground to set them. Don’t wait until the trap snaps shut, but go to the next location. The traps are marked on the map so you can return to them anytime. If a bird is trapped in it, you'll recognize that with a highlight over the cage. Collect the cages so set again and bring them to the huntsman, who will reward you with some groschen.