probably a magic tree seed, which is worth around 200k coins.
You use a Pestle & Mortar, you can get this from Herblore shop in Taverly.
erm, do you mean the random event type birds nest. These happen when wood cutting, particularly the maple and yew trees near Seers village and Catherby
Themselves - it's a natural thing all birds do
It all comes down to the amount of xp you gain. At a certain amount of xp you will get a nest, so the best tree/woodcutting thing to do is ivy to get birds nests, as it gives you 332.5xp per cut, however this is only fast a higher levels so a lower level tree will get you more xp (and more nests) because you are cutting faster and gaining more xp an hour.
cutting trees sometimes a nest will fall and there will be either seeds, a ring, bird egg, or, gem in it. im not sure if a gem is a nest drop correct me if im wrong.
In Runescape bird eggs can hatch into either Saradomin owl, Zamorak hawk, or Guthix Bird depending on the color. To get them to hatch you need 70 Summoning. Yo can get a bird egg by randomly getting one in a Birds nest from a tree. Links below
The nest was built by birds.
it looks like a birds nest
Te specific study of the birds nest is calle "ornithology".
Best thing to do is allow them to nest, then remove the nest when the young fledge.
Many but the best known are probably weavers and oropendolas
Birds mate after and before making a nest