They can learn any songs a human will sing to them and will be able to sing a song pitch perfect after only hearing it once. Those songs serve as a shared-memory that is passed on from troll to troll. The song can last about ten minutes and is referred as the short call but it also can last a month, referred as the long call.
The people of Happy Landings found out that the trolls get nervous around big human communities, the limit being one thousand, eight hundred and ninety humans. Past this limit, the trolls will simply go away and only comeback after the population dropped under this limit.
They are described to have chimp faces, and black, hairy body with a wide chest, a big head and enormous hands the size of tennis rackets.
In Happy Landings, humans have been living alongside trolls for centuries with the trolls helping them with manual labor like carrying heavy loads.
Before Step Day and Lobsang and Joshua Valienté's journey, only few people, like Sally Linsay knew about their existence (except rare incidents like with Private Percy Blakeney who lived several decades with trolls and thought they were Russians).
Sally, fond of the trolls, soon noticed, fifteen years after Step Day, that the trolls were migrating East for an unknown reason. In order to find the reason behind it, she seeked Lobsang and Joshua's help and embarked on the Mark Twain.
Lobsang, in order to prevent the creature to reach Datum Earth, merged with it and diverted her course.
In 2040, trolls had become an ever-present in the stepwise worlds colonized by mankind. They are willing and clever workers who help tend to clear fields, build schoolhouse, help in sheep farms like in stepwise Australias and even work in the assembly lines of factories in some Low Earth Americas.
But as mankind spread across the Long Earth, incidents between humans and trolls began to happen more and more often. One of the most iconic incident was when Mary, a troll female residing at the GapSpace facility, killed one of the GapSpace researchers who tried to force her to give away her cub.
This incident, among others, prompted Sally Linsay to reach out to Joshua Valienté and ask him to go in front of the Congress on Datum Earth to ask for the creation of a protection law for trolls.
While Maggie Kauffman, aboard the USS Benjamin Franklin, was solving more and more incidents involving trolls as much as she could, in June 2040, the trolls, swapping information with the long call, finally reached the decision to leave the worlds with humans in it.
This is why Lobsang summoned Joshua to Madison West 10, to a transEarth Institute facility, where he asked him to go find Sally and Monica Jansson, who disappeared with Mary and Ham, find the trolls and convince them to give mankind a second chance.
The trolls were eventually found on Earth West 1,617,524, the beagles homeworld, and there Joshua and Bill unpacked a translator box looking like a tablet that with a message part human and part troll where a hologram of Lobsang apologized in the name of mankind.
According to Maggie Kauffman's observations of the family of trolls she kept aboard the USS Benjamin Franklin and now aboard the USS Neil A. Armstrong II, trolls could sense danger coming well before humans could respond, like the imminence of Jokers.