Dupont’s Lark males start to sing earlier but reduce song rate on full moon dawns

Abstract

Moon phase affects the ecology and behaviour of animals and may thus affect both circadian and circannual rhythms. Its influence on nocturnal and dawn bird behaviour is known, but fewer studies have examined its effect on passerines’ singing activity, some of which have yielded contradictory findings. With the aim of elucidating whether moon phase affects dawn singing in passerines, we recorded dawn singing activity of the Dupont’s Lark Chersophilus duponti in three mediterranean shrub-steppes, through repeated sampling over three lunar cycles per breeding season in 2 years. Our results corroborate the idea that moon phase affects signalling behaviour of passerines. We found that, on average, dawn singing started 15 min earlier when the moon was full, due to variations in the light intensity, which seems to act as a trigger for singing activity in the Dupont’s Lark. Nonetheless, the dawn chorus finished at the same time regardless of moon phase, maybe due to a low contribution of moonlight as sunrise approaches. As a consequence, performance time increased during full moon nights. However, the total production of songs did not differ between moon phases, and therefore, song rate was lower during full moons. Reduced song rate on full moon nights could be a response of singing males to reduce their predation risk, since singing on bright nights can increase the ability of predators to locate them, but it could be also related to the energetic cost of longer choruses. The consequences of moon phase for mate attraction, reproductive success and behaviour in this and other bird species remain unknown, and thus our research can serve as a starting point from which to develop new studies.