(a) Comparison of daytime noise levels between locations where robins sang nocturnally (mean=62.68 dB, 95% CI=60.15–65.21 dB) and those where singing occurred during the day but not at night (52.87, 50.93–54.81 dB). (b) Night-time light levels at locations where nocturnal singing robins were detected (2.42, 1.98–2.86 lux) and those where singing activity was detected during the day but not at night (1.78, 1.4–2.15 lux). (c) Daytime noise and night-time light levels at 121 locations across urban Sheffield. Filled circles indicate locations with birds singing day and night, filled triangle indicates night-singing only, open circles indicate day-singing only and grey circles indicate places where no singing activity was detected by day or night.