Light Pollution and Thrush Decline

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Colin Henshaw
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Light Pollution and Thrush Decline

Post by Colin Henshaw »

Thrushes have been in decline for several decades, and this was brought home to me by my late father in the mid-1990's. He commented that he hadn't seen a thrush in our garden in Gatley, Cheshire, for about ten years.

The fact that thrushes have declined has been sumarised here:

http://www.springerlink.com/content/t24070u7x6r54n21/

I contend that light pollution is one of the contributory factors, in addition to habitat destruction and pesticides. Lights attract insects, and if not killed outright by the heat from the lights, they will spiral around them until they drop, too tired either to feed or to procreate. Lighting will attract insects over a wide area, so over long periods of time will cause insect populations to decline. The decline in insects over the past five decades or so correlates negatively with the expansion of street lighting systems nationwide, and this has been confirmed by environmental groups such as Butterfly Conservation and Bug Life. This decline in insect populations will have concomitant effects on animals dependant on them, such as birds, amphibians and insectivorous mammals such as bats.

The decline in the number of thrushes was probably brought about by this decline in insects. Most birds like a varied diet, and it is well known that thrushes eat snails. However they would not like to eat snails alone.

As the insect population declined the thrushes had less to eat despite the presence of snails in some areas. This resulted in a decline in thrushes, possibly compounded with habitat destruction and pesticides as I mentioned earlier. With thrushes having been taken out of the equation, this could possibly explain the explosion in common garden snails (Helix aspersa) in areas where they never existed before. During my early years in Gatley - 1950's and 1960's snails were almost unknown, and were only seen on trips to rural areas, usually coastal. By the late 1990's they were very abundant and other snail species had moved in, such as Cepaea nemoralis and Cepaea hortensis. I even found an example of Arianta arbustorum, at (Gatley Carrs, and subsequently in Bowdon), which as far as snails go, was never common. This explosion of snails was reported all over southern Manchester and northeast Cheshire. I even found a common garden snail outside the Bull's Head pub, about 100 metres from Piccadilly Station in Manchester. This snails was rescued and subsequently liberated in Bowdon. The snails probably invaded the suburban areas along railway tracks that linked the suburbs with the surrounding rural areas where they were more common.
Deimos
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Post by Deimos »

Similar thing (in a way) on Countryfile (TV) a few weeks ago where in Scotland some species of sea bird (cannot remember which species) was being attracted by the mainland port lights at night, flying to the port and landing and then they could not take off again (some birds cannot take-off from a hard flat surface - nature of their wings/aerodynamics).

However, in fairness to that particular port t was a fishing port active at night so they did need and were using the lights (unlike many street lights at 03:00 am), plus there were a voluntary group of people rescuing the birds and releasing then elsewhere.

But it does show how lights at night can interfere with nature.

Ian
M54
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Post by M54 »

Thrushes where I live like fruit and are active by day not night.
Lights attract night flying insects, since that is when they are on, even if on during the day the sun tends to be brighter by quite a significant amount.

Also thrushes are known for smashing snail shells to get the snail and not a lot of them fly around street lights.

So cannot see a connection. Except for the "we have more lights and less thrushes so lets make a link."

Thrushes are part of the blackbird family and are therefore woodland birds. Towns and cities would not suit them greatly and we have removed lots of suitable habitats in the form of hedgerows. Now that would affect them but I cannot see lights doing a great deal if anything.
Lady Isabella
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Post by Lady Isabella »

While a Thrush will eat insects, it is not their main preferred source of food. If a Thrush is having to resort to eating lots of insects, then this is an unsuitable situation for the species.

My family has been involved in agriculture for the last 150 years, and the biggest effect that we have seen on Thrush populations has been Farming and Woodland management practices, which is/has been robbing the bird of its habitat.

Just after the Second World War, chemicals became more affordable and we started to use them on the land. Then slowly in the 1950's we started to notice a decline. this was also observed by others at the time. The Thrush population was then hit hard by a bad Winter in the early 1960s. Then just as the bird was struggling to make a come-back, we had the situation in the late 60s early 70s where vast amounts of hedgerows were ripped up and drainage systems installed to make way for enormous sized fields. With these super sized fields came yet more chemicals and destruction of the habitat.

The British Trust for Ornithology reports a major drop in numbers from the mid 1970s. With the drop being most noticeable in farmland, the same time that intensive farming practices were being conducted. Back in the 70s, even large towns had little in the way of light pollution and certainly not countryside locations.

On top of all this then came Woodland management practices that destroyed the habitat needed by the Thrush. In recent years the situation has started to improve slightly and we are now starting to see numbers increase. I know of other individuals and groups who have now started to report the same thing. So hopefully the decline has been halted, and with better conservation and farming practices the poor old Thrush will at least have a chance.

While light pollution has increased in recent years, so too has the spread of urbanisation, with that comes yet more destruction of habitat. For our family the decline in Thrush numbers first started back in the 1950s. and coincided with the change in farming practices which were brought in as a result of World War 2
and the need to feed the people of post war Germany. By the 70s we were feeding the people of the Eastern block and Soviet Union countries. Sadly it was the British wildlife that paid the price for all this intensive farming.
Colin Henshaw
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Thrush decline

Post by Colin Henshaw »

Some interesting posts here, confirming the effect of pesticides and habitat destruction. I am not denying that these factors are part of the problem. And yes, increased urbanisation with associated habitat destruction goes hand-in-glove with increases in light pollution. However, I do feel light pollution is a contributory factor. It has been increasing steadily since the 1950's so this further ties in with thrush decline beginning at that time. I have seen how lighting sucks up insects out of the environment, so I remain convinced that along with the other factors mentioned above, that it is a major part of the problem that has largely been ignored. Birds need insects to feed their young and provide them with protein. This has been reported with sparrows, and if insect numbers decline this will have a concomitant effect on predators higher up in the food chain. The problem is multidimensional, and what I am simply trying to say is that light pollution is part of it.
Colin Henshaw
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Thrush decline

Post by Colin Henshaw »

Light pollution was already substantial by the late 1960's as I recall very well. From Gatley the sky was already glowing orange from the extensive street lighting system that had already been installed in Greater Manchester. Some nights the glow from the cloud ceiling would pulsate in response to a single gas flare at a chemical plant in Carrington. This was visible from all over the Manchester area. In 1974 I looked out over the Irish Sea one night from Cemaes Bay in Anglesey, only to see a glow on the horizon that could only have come from a city. I took a compass bearing on it and confirmed it was Dublin. Light Pollution was already a problem and astronomers were beginning to complain about it. However, we all need street lighting don't we? It reduces accidents and crime doesn't it so we can't do without out beloved street lights. With public attitudes like that astronomers felt impotent to do anything about it. It was only towards the end of the 1980's that they began to militate against it. Because of this the lighting industry was persuaded to start manufacturing some dark sky compliant lighting, but there is still no universal obligation to apply it, so the problem may well get worse before it gets better, (if ever it will). Light pollution was even a problem before the 1960's which is why the Royal Observatory decamped from Greenwich to Herstmonceux.and by the late 1970's it was felt necessary to shift the INT to the Canary Islands.
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