A fledgling owl that lived 47 million years ago in what is now Germany is offering new clues about when most owls became nocturnal, Live Science reported. The bird is a newly described species, Masillastrix blattophaga, unearthed in 2025 in the Messel Pit, an ancient lake now regarded as the richest fossil site in the world for life in the Eocene epoch (56 million to 34 million years ago). The skull is missing, but the rest of the fossil was so well preserved that researchers found the owl's last meal in its stomach: a greenish-blue, iridescent cockroach. The study was published Nov. 2 in Current Biology.
Iridescence is associated with a diurnal lifestyle, so the tiny owl, less than 5 inches (12 centimeters) long, appears to have been hunting in the daytime, the authors said. "There exists a consensus that owls must have evolved from a diurnal ancestor," first author Gerald Mayr, a paleontologist at the Senckenberg Research Institute and the Natural History Museum Frankfurt, told Live Science. Some early owl fossils have head-rotation structures similar to those of diurnal raptors and bony ridges above the eye sockets that could have shaded their eyes from the sun. Mayr said it is plausible the Messel owl was fully diurnal, rather than active day and night as some owls are today, because a mixed schedule would imply that some ancestors had already evolved nocturnal traits. Researchers also found a cockroach identical to the one in the stomach in sediments a few feet from the fossil, which helped them identify the insect.
It is possible the bird ate at dawn or dusk, which would weaken the daytime case. Other clues, Mayr said, include the appearance of some feathers and the stoutness of the upper wing bones, or humeri. The team believes stocky humeri hint that the species flew by day, when silent movement is less of an advantage because there is enough light to see predators. Modern nocturnal owls have slim humeri and fly almost soundlessly. If that hypothesis is right, the earliest known nocturnal owl species are from about 35 million years ago, in the Late Eocene, and look more like modern owls, with elongated humeri. The oldest known owl, Ogygoptynx wetmorei, dates to around 60 million years ago. That would put the shift to night between 47 million and 35 million years ago, the best current estimate, the study said, because the owl fossil record is sparse.
The remaining question is why. Earlier theories suggested owls went nocturnal to avoid competition with daytime birds of prey or to take advantage of a rise in nocturnal mammals. But those groups exploded much later, around 20 million to 25 million years ago, so there was no obvious advantage at the 35-million-year mark. "By narrowing down the time frame when owls became nocturnal, our study may eventually contribute to solving this mystery," Mayr said. The verified claim is a well-preserved daytime-leaning owl from 47 million years ago, not a final answer to why the night shift happened.