The guano piles have Smaug-like depth and richness. If dragons cared about agriculture they would all be occupied. Soil-fixed nitrogen is a as rare underground as everything else. Hip-high forests of pale pigmentless plants die even as they grow in the rich but sunless soil. A big Lamanter nest hangs above a dangerous oasis of organic life. Throngs of insects, big and small, and all the things that feed on them. Kept safe from organised intelligence by the Lamenters terrible cry. And the dead.
There are deep dwelling albino Oilbirds, these are thinner,more ragged, and often blind. They are descended from captured young, raised by underground civilisations in attempts to farm the useful oils they hold.
Every so often a city dwelling race gets the idea of farming Lamanters. The chicks are so full of oil, you can kill one, squeeze it out, and use the unrefined bloody mess to fuel a lamp for days. Light is a fine currency for some.
This never works. Factors preventing the useful farming of Lamenter's are:-
1 They can fly and will leave.
2 They are man-sized and will peck your face off.
3 They will defend their young with their life.
4 They can navigate underground when they want to, using a stream of extremely high pitched tongue clicks five octaves above middle-C.
5 The cacophonous screaming of Oilbirds en-mass will drive any intelligent being insane.
6 They are surrounded by the invisible souls of the dead at all times.
(Drow agricultural rumours* tell of Aboleth treaty’s and farms of mad, skinless men covered with peck-marks, tending baffled white birds in dark Cyclopean dovecotes. The resulting clamour keeps sane things away from the area, which can be handy for those on whom sanity has no hold. Deafened pack-apes toil in epic oil-caravans to the sighted realms)
Insanity is their chief defence. A flock of howling Oilbirds weave a nexus of high-frequency ultrasound that deafens, frightens, invades the mind and ultimately drives you mad.
But this is not its purpose. No sage has ever known knows what the birds sing to the dead. But I will tell you now. It is a love song. They are crying to their lost children and lost loves. And they are heard
When you die in the presence of Lamenters the hideous music shifts. Its shaped like that to echo in the baffles outside life. When you cross over, from the other side, it is beautiful. Like dawn-song held in autumn air. You will probably want to stay there too, if you have no-where else to go.
Survivors of the Oil-Birds Song often become silent fungal shaman.
Characters who go to Zero HP while under the Lamenters song and then survive, no-longer suffer insanity as a result, and feel a little bit better about life in general. Not everything is awful all the time.
*Drow farming rumours are some of the darkest rumours you can get anywhere. Like a pro-slavery version of Roots directed by David Lynch.