City blackbirds are becoming reproductively mature earlier than rural birds, which is thought to be due to artificial light at night.
- Humans have the ability to avoid light pollution to some extent by closing curtains or using eye-masks, but urban wildlife is unable to avoid night-time light.
- Researchers tracked wild birds from city populations and from rural populations and then placed them under controlled laboratory conditions. Male blackbirds from the city were reproductively mature almost a full month prior to country birds. The breeding season for this species is approximately three to four months long so a head-start of a month is likely to be significant for urban blackbirds.
- Although the affect of altered light cues have been recognised and utilized in the past (e.g. to increase egg production in chickens), this study indicates just how sensitive birds can be to light-based cues as impacts were observed at light intensities 20 times less than that emitted by a single street light.
Implications and next steps: This study indicates that urban light pollution is altering environmental cues in birds and having impacts which may be of interest for street lighting policy and lighting policy in the planning regime. There may also be implications of human-induced lighting for urban wildlife other than birds.