In 2013 a team of researchers from the San Diego Natural History Museum completed a five-year survey of the Grinnell Transect, Grinnell's 1908 study of the flora and fauna of Mount San Jacinto. In 60 surveys across 20 sites, they found the forest to be much denser than in Grinnell's time, with the loss of three species including a flying squirrel, and an increase in birds that like thick brush, such as the hermit thrush, the brown creeper and the Townsend's solitaire. The relative lack of leaf litter and decayed ground cover in Grinnell's time was considered to make the occurrence of hot and lasting fires in the forest impossible. With a much thicker understory in 2013, the team of researchers were forced by the Mountain Fire to evacuate their camp.