1. What is a heretofore unknown secret of Troll ecology?
Hmmm... what are trolls? There are numerous creatures around the world which have been identified as "trolls" or at least "troll-kin" by cryptozoologists. Many of these creatures fall into the wider category of elementals, with the most common variety of "troll-kin" fitting into the intersection of the earth/stone and darkness elemental subtypes (hence the legends of them turning to stone in sunlight). In darkness they live, in bright light the animating darkness is dispersed and the stone dominates.
What few realise is that there are other troll-kin who are far more ephemeral in nature, and which are often mistaken as other beings entirely. The air elemental subtypes fade away on the breeze when sunlight illuminates them, the fire subtype rapidly incinerates itself, and the water subtype splashes as a puddle often absorbed into the ground. Since the stone-affiliated trolls are those most likely to leave remains, they are the ones most commonly known to folklore.
Ancient Fire Troll
Similarly, there are said to be troll-kin who exist between light and the cardinal elemental forms. But while a dark troll-kin can hide from the sun for the hours of daylight, a light troll-kin cannot hide from the darkness during the hours of night (except at the polar regions during nights of endless sun). This means most light affliated troll-kin barely survive longer than a single day, and even those at the poles don't survive longer than a few months. The small size of young troll-kin means that most light affiliated trolls are mistaken for flightless sprites, because it takes many years for a troll to reach it's full size (and the form traditionally recognised as a Troll). It is said that in recent decades, light affiliated troll-kin have maintained their animus through the use of UV and Fluorescent light sources, but any technologically inclined cryptozoologists who might be likely to release documented evidence of this haven't done so thus far.
Mature Water Troll
Those creatures which do not revert to elemental forms when their elemental animus is dispersed are not true trolls, but many scholars and cryptid hunters still debate this point.