Corvo cuts public lighting to protect fledgling Cory’s shearwaters
The story at a glance
On Corvo in the Azores, public lighting is reduced during the autumn fledging period for Cory’s shearwaters. The local effort is paired with volunteers rescuing birds that become grounded after being disoriented by lights. 1
Monitoring has produced encouraging but preliminary signs: most recorded accidents involving disoriented juveniles occurred when public lights were on. The available records do not establish how much the blackout itself changes survival or population trends. 23
What you need to know
- Corvo has used seasonal lighting reductions since at least 2017. The measures have included wider reductions, a full-night blackout in 2019 and a five-night blackout in 2020; the Guardian describes a recurring five-night autumn blackout since 2019. 1
- Artificial light can disorient fledgling Cory’s shearwaters, causing them to fall or become grounded. A 2011 study estimated that urban light caused mortality in about 6% of fledglings across the Azores, with variation between islands. 4
- The same study reported that light-related mortality could fall below 0.5% when rescue campaigns were operating. That finding concerns rescue campaigns and does not isolate the effect of Corvo’s blackout. 4
- SPEA reports that 85% of recorded accidents involving disoriented juvenile birds on Corvo occurred while public lighting was on. The organisation describes this as preliminary monitoring, not a controlled comparison. 2
- Project records list 662 shearwaters rescued on Corvo during the 2020 campaign, with 17 found dead. They also record nine falls during the week of a general blackout, but do not show that the blackout alone explains the lower count. 3
Why this matters
The Corvo effort combines a practical reduction in a known pressure with rescue work and monitoring. It offers a local example of action against light-related fledgling mortality, while the limits of the available evidence underline the importance of checking whether fewer recorded falls translate into better outcomes for birds. 124
What happens next
The key evidence need is a comparison of grounded birds on blackout and non-blackout nights that accounts for weather, fledging peaks and rescue effort. Following rescued birds after release, and tracking population trends over time, would help establish whether the measures produce lasting benefits. The sources reviewed do not report those results. 1234
What we know
- Corvo has implemented seasonal public-lighting reductions during the Cory’s shearwater fledging period. 13
- Artificial light can disorient fledglings, and rescue campaigns are a relevant mitigation measure. 14
- SPEA’s preliminary records associate most recorded accidents involving disoriented juveniles with nights when public lighting was on. 2
What we don't know
- The sources do not establish the blackout’s independent effect on the number of birds grounded or killed. 23
- The records reviewed do not show whether rescued fledglings survive after release. 14
- No population trend evidence for Corvo is provided to show whether the local measures have benefited the shearwater population over time. 14
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