Evidence for diurnal habits in an exceptionally preserved Eocene owl

It is poorly understood when owls (Strigiformes) became nocturnal, which impedes considerations of the evolutionary reasons behind this distinctive behavior.^1,2 Here, we report an extraordinary owl skeleton from the middle Eocene of Germany, which preserves remains of an iridescent cockroach as stomach contents-the first identifiable insect remains ever found as the last meal of a fossil bird. Because iridescence is correlated with diurnal habits in cockroaches,³ the fossil provides the strongest evidence to date for diurnality in archaic Strigiformes. Further support for a diurnal ecology comes from the absence of barred flight feathers as well as the lack of frayed leading edges of the primaries; the presence of these features is associated with nocturnality in extant owls.^4,5 The humerus is much stouter than in extant owls, indicating that the wings were less adapted to silent flight. Conversely, a slenderer humerus suggests that late Eocene owls had shifted toward a nocturnal ecology. This timeframe rules out previously suggested factors for nocturnality in owls² and constrains the origin of an ecological hallmark of these birds.