After a forest is logged, that land is often re-planted with new saplings. Within a few decades, those trees will have grown pretty big, and the forest will look much like a forest once again, with birds singing among the shade of the boughs. But a new study finds that, despite this apparent rebirth, younger forests may not offer those birds the same quality of habitat as an old-growth forest—with differences between the two forest types stretching all the way down to a cellular level. Researchers in Latvia compared wild forests more than 100 years old with managed pine forests just 40-50 years old. They studied how many insects were living in each forest type by measuring the amount of frass (insect poop and other droppings) that fell from trees. They also took blood samples from 15 day-old great tits—a common European songbird—to measure the birds’ stress levels.