The paper is entitled "Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds", and is authored by Jingmai O'Connor, Zhou Zhonghe, and Xu Xing. The paper is based on an awesome little fossil that preserves an enantiornithine bird head-first in the gut of a microraptorine. Because most enantiornithine birds seem to have been arboreal, the authors conclude that the Microraptor individual was likely hunting in the trees, and therefore potentially arboreal. There are some potential gaps in this conclusion, particularly that modern arboreal birds are actually often predated on the ground (where they are more vulnerable) but it's an awesome specimen, regardless. Direct evidence of feeding behavior is very rare as fossils, so this is a special case, indeed.