Abstract: The importance of nocturnal display in diurnal birds has been neglected for a long time, owing to the difficulties in recording behaviour by night. Using loggers with an accelerometer (ACC) we studied nocturnal display in male African houbara bustards, Chlamydotis undulata, ssp. fuertaventurae. Diurnal display of male houbaras consists of a visual component, the display run, and an acoustic component, the boom. Nocturnal display runs were only recorded twice, both on full moon nights. Nocturnal booming intensity was highest on full moon nights when it reached similar levels to those during peak diurnal display at dawn. The more favourable physical conditions for sound transmission and the reduced acoustic competition with wind and other birds at night have been proposed to explain nocturnal vocalizing. Minimizing copulation disruptions, a frequent intramale competition mechanism in bustards, could be an additional advantage of nocturnal display. However, these factors do not explain why vocal activity is highest on full moon nights. We suggest that moonlight may help displaying males to detect predators, as well as to communicate visually with approaching females. Moonlight also allows males to combine booms with visual signals produced by the white neck feathers exposed during booming into more efficient multimodal signals. Moonlight would thus ultimately lead to males achieving nocturnal copulations, which indeed might be more frequent than previously thought, according to rates of nocturnal ACC-recorded precopulatory movements. Finally, nocturnal booming sequences had almost twice as many booms as diurnal ones, which suggests that nocturnal vocalizations transmit higher-quality information about signalling males than diurnal vocalizations. Nocturnal booming significantly increased the total display time of male houbara bustards; thus, future studies should investigate whether nocturnal vocal activity represents an important contribution to individual fitness in this and other nocturnally vocalizing diurnal species.

Abstract: Cereus peruvianus (Peruvian apple cactus) is a large erect and thorny succulent cactus characterized by column-like (cereus [L]: column), that is, candle-shaped, appendages. For three successive years (1100 days), between early April and late November, we studied the flowering patterns of eight cacti growing in public gardens and rural areas of north and central Tunisia, far from nighttime artificial illumination, in relation to natural environmental light, temperature, relative humidity and precipitation parameters. Flower blooming was assessed nightly between 23:00 h and until at least 02:00 h, and additionally around-the-clock at ~1 h intervals for 30 consecutive days during the late summer of each year of study to quantify both nyctohemeral (day-night) and lunar patterns. During the summer months of prolonged daytime photoperiod, flower blooming of C. peruvianus exhibited predictable-in-time variation as “waves” with average period of 29.5 days synchronized by the light of the full moon. The large-sized flower (~16 cm diameter) opens almost exclusively at night, between sunset and sunrise, as a 24 h rhythm during a specific 3-4-day span of the lunar cycle (full moon), with a strong correlation between moon phase and number and proportion of flowers in bloom (ranging from r = +0.59 to +0.91). Black, blue and red cotton sheets were used to filter specific spectral bands of nighttime moonlight from illuminating randomly selected plant appendages as a means to test the hypothesis of a “gating” 24 h rhythm phenomenon of photoreceptors at the bud level. Relative to control conditions (no light filtering), black sheet covering inhibited flower bud induction by 87.5%, red sheet covering by 46.6% and blue sheet covering by 34%, and the respective inhibiting effects on number of flowers in bloom were essentially 100%, ~81% and ~44%. C. peruvianus is a unique example of a terrestrial plant that exhibits a circadian flowering rhythm (peak ~00:00 h) “gated” by 24 h, lunar 29.5-day (bright light of full moon) and annual 365.25-day (prolonged summertime day length) environmental photoperiod cycles.