The study, led by researchers at Lund University, reveals that moonlight is a critical factor for the red-necked nightjar (Caprimulgus ruficollis). Published in Science Advances, the research shows that at full moon, the bird can hunt insects almost all night, taking advantage of the bright conditions to feed continuously. But during dark nights, when the moon is new or obscured, the bird is forced to hunt only in short periods at dusk and dawn.
To further conserve energy on moonless nights, the nightjar slows down and lowers its body temperature, entering a torpor-like state that reduces its metabolic rate. This physiological adaptation is crucial because the bird's energy budget is tightly constrained; without sufficient moonlight, it cannot acquire enough food to sustain itself. Furthermore, the study found that moonlight is essential for migration, as the birds time their long-distance flights to coincide with bright lunar phases.
Unlike bats, the nightjar lacks the ability to navigate effectively in total darkness. This is an animal that lives on the edge. Without moonlight, the energy budget simply doesn't add up.
Breeding is intricately synchronized with the moon's rhythm. Eggs are laid so that chicks hatch when nocturnal insect availability is greatest, typically around the full moon, ensuring a plentiful food supply for the growing young. Unlike bats, which use echolocation to navigate and hunt in complete darkness, the nightjar lacks such sensory adaptations and relies heavily on visual cues.
According to Anders Hedenström, a biology professor at Lund University, the bird lives on the margin; without moonlight, the energy budget simply doesn't add up. The findings are based on ten years of fieldwork in Doñana National Park in Spain, where the birds were tracked with multi-sensor data loggers developed at Lund University, which recorded the birds' movements, body temperatures, and light exposure, enabling the team to correlate behavior with lunar phases. Nocturnal animals are vulnerable to changes in the light environment, the researchers noted, and artificial light pollution could disrupt their delicate ecological balance.
However, the specific threats from artificial light pollution or cloud cover remain unclear, and it is unknown whether these findings apply to other nocturnal migratory birds. Conservation measures based on the study have not yet been proposed, and the study does not quantify the exact effect of reduced moonlight on survival or reproductive success.