We continue to learn more about the damaging impact of light pollution.
Most recently, an Australian study – the first, the researchers say, to measure neurological responses to artificial light in wildlife – has shown how it can disrupt the length, structure and intensity of sleep patterns in birds.
And that applies not just to white light, but also to amber light, which is considered more “sleep friendly” and thus often used for that very reason.
A team from La Trobe University and University of Melbourne used miniature sensors to measure brain activity in magpies and pigeons, which both average 10 hours of sleep a night.
“When experimentally exposed to light at night at intensities typical of urban areas, domestic pigeons (Columba livia) and wild-caught Australian magpies (Cracticus tibicen tyrannica) slept less, favoured non-rapid eye movement (NREM) sleep over REM sleep, slept less intensely, and had more fragmented sleep compared to when lights were switched off,” they write in a paper in the journal Current Biology.
However, the magnitude varied between species. La Trobe’s John Lesku says magpies lost more NREM sleep under white light than amber light, while pigeons lost around four hours of sleep under both types of light
Neither species fully recovered sleep lost, with impacts on their ability to forage for food, fight off predators and search for mates.
“Our experiments demonstrate that realistic intensities of urban light at night can disrupt sleep in birds,” the researchers write.
“Importantly, many of these effects – including the distinct effects of white and amber light on sleep in magpies – would have been impossible to detect by measuring only the total amount of sleep or sleep behaviour…”
They acknowledge that they investigated the effects of light exposure in a context where birds couldn’t avoid it, and thus couldn’t tell whether they habituate to light at night or would otherwise avoid intensely lit areas if able to.
“Nevertheless,” they write, “the less-disruptive effects of amber lighting on sleep in magpies, but not pigeons, within a very similar experimental environment emphasise the need for research beyond single ‘model’ bird species.”
Similar arguments have been made, they add, by researchers working with reptiles.