In her second poetry collection, Didi Jackson shifts among lyrical strategies, sometimes earthy and elsewhere mystical. An assistant professor at Tennessee’s Vanderbilt University, she spends part of the year in Rochester, Vt., and many of these poems are meditations prompted by hikes in her Green Mountain surrounds. Here, she finds a quivering, sentient landscape busy with birds — sapsucker, kingfisher, yellow-rumped warbler — recurring companions for a writer fascinated by times of transition, dawn and dusk…