So I found some of those bird nests, one around Skalitz and two around Rattay. One had only one groschen in it but another had a necklace worth 1000 groschen (!) in it. Now my question is, what are those nests? Can you get loot every now and then from them? And what is the best way to sell the necklace? Some merchants give me around 200, others give me around 400 groschen. Is there someone specific I have to sell it to, or is there something like a haggling skill I need in order to get better prices?
it is just a nice collecting game.
it can be very rewarding! you have to take your time and try to shoot them with an arrow in order to pick the loot. most time it will be rubbish but from time to time maybe you are able to collect a n expesnive juwelery out of it, as you did.
1000 Groschen? that is the Jackpot i would say, congratulations.
you have to try different merchants, different cities, just try to sell good Price and enjoy
I believe you need to have good reputation with a merchant so he will give you more groschen.
Also your Speech skill has some influence afaik
if you want to get most Money put your armor off, wash yourself, in Barrels at least better in bath house and put on noble clothes.
go t a City where you helped a lot, for example because of mainquest all guards in talmberg do know my Name and greet me with my Name i am very welcome. that way you get good Prices here.
in other cities i am flagged as a thief or get searched if i Approach it, wont get good Prices here.
last but not least, with merchants you can easily get good reputations just sell them many things cheap, bargain and take less Money than they pay, with useless stuff. they will like you " Mr. cheap Price". if you now have something Special to sell they will listen to you and give you a good Price, “mr. trustful goods” 
Ok thanks. I just thought the nests are special hiding spots for thieves or something like that. I’ll definately try out those tricks, thanks again.
Wait what. There is loot in them there nests… girrmme that sweet loot.
Yep,
the more Rep the more Cash
The loot from the Birdnests appears random, from a Cobweb to a Necklace value of 1073g so always worth checking them out. Though the nest I found mine in may spawn it always or more often from some other posts.
I found the Necklace in my very first nest and made the 10 minutes stunbling around in the dark at night without a torch worthwhile 
Thieving magpies…
Lots of bird nests?
Well birds eat bugs, and if this game has a lot of bugs then there dietry needs are fullfilled and overpopulation shall occur.
As the game is patched to contain less bugs their population base should waiver, and maybe eventually decline.
I like game. tastes nice with some herba and a slow roasting.
(puns aside- how could I not?)