Trip reports

Robins and street lights - Friday December 2nd

Robin - RSPB Images

Friday, 2 December 2011

Robins and Street Lights was the title of the talk that Alex Pollard came to give to the group on Friday December 2nd. This title did not give a true picture of the breadth of her talk. She covered not only robins but bats, mice, turtles and even down to plankton.
She began by defining light pollution: Light pollution is the alteration of light levels in the outdoor environment (from those present naturally) due to man-made sources of light.
We saw satellite images of the earth at night which graphically showed the huge swathes of the earth bathed in artificial light.
Some bats such as horseshoes, shun street lights and will disappear from areas when lights are introduced. Here were turtle hatchlings whose tracks showed that they were wandering in circles instead of making for the sea, confused by beach lights distractions. The two light beams, memorials to the twin towers were columns of birds swirling, trapped in the columns of light. This was similar to the effect of birds trapped in lighthouse beams.
Plankton rise and fall to the rhythm of the sun and moon. Lights upset this rhythm and the food chain is disrupted. Amphibians generally will not breed in light. Street lights may adversely affect the breeding pattern in urban ponds - an increasingly important reservoir for amphibians.
But, back to the subject.
Alex chose robins for many reasons both sexes sing throughout the year, they're easy to train, they have good vision, they're widespread and Alex likes them!
To investigate the effect of street lights Alex had 2 groups of robins. One in cages darkened and artificially lit, the other exposed to daylight.. Both sets of birds had 24hour access to food and were weighed each time they landed on the food source to feed.. It seems that both sets of birds lost on average 10% of their bodyweight overnight. The birds were then swapped over and the pattern repeated itself. So, street lights may get birds out foraging earlier. On the other hand they are more visible to predators.
The effect on singing is highly variable. Studies show some birds sing earlier than the natural dawn. Others wait till that burst of song is over before they start.
So what to do? The obvious answer is to cut light pollution. This will minimise adverse effects on wildlife, it will save money by only lighting when and where necessary and a better design of fitting will cut the amount of energy needed to illuminate an area.
Thanks therefore to Alex for a most illuminating and educational talk. From the questions during the talk it seems all there enjoyed it.
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This was the last meeting of 2011and everyone present thought it a good end to an entertaining year.
Pete Elkington