Saturday, 30 May 2015

Having a light meal!

Although it couldn’t be described as common the Blue Rock Thrush is a widely distributed species in the Algarve and is usually not difficult to find.

It is perhaps mainly associated with the sea-cliffs and rocky coastline of the western Algarve but it also occurs elsewhere, breeding in steep-sided, rocky valleys, in quarries, on ruined buildings and on churches and other large, town-centre buildings.

In the quarry

We have been watching several pairs in recent weeks around Tavira and further inland.  In March, we were even able to watch one from our kitchen window as it sang from the roof of a building across the road.

Feeding young

In the centre of Tavira a pair has been seen on the Church of Santa Maria do Castelo.  These birds have been notably inactive during the day but they come alive each evening at around 9.00pm (half an hour after sunset) when the floodlights that illuminate the church are switched on and immediately attract many moths and other flying insects, which are ready-meals for the thrushes.  Although this behaviour and feeding strategy doesn’t seem to have been previously documented for Blue Rock Thrushes, it is not, of course, unusual these days for birds’ lives to be affected by artificial light sources such as street lamps and floodlights, leading to extended feeding hours and for some species extended periods of singing.

At the church (ISO 6400; f/5.6: 1/200 sec)

Church of Santa Maria do Castelo

Another species taking advantage of the abundance of insect prey at the church in Tavira is Red-necked Nightjar.  Twice this week we have seen a bird hawking insects from a high tree-top perch next to the church.  After each aerial sortie it returns to the same perch in the manner of a Spotted Flycatcher and it has used the same perch on successive evenings.

On a ruined building

The floodlighting at the church is clearly making life easier for the Blue Rock Thrushes and Red-necked Nightjars but spare a thought for the moths and other insects.  It has been estimated that up to 30% of insects attracted to such lighting die or are injured by colliding with a hot lamp surface or as a result of predation.  Artificial lighting can have several other negative impacts on a wide range of invertebrates including disrupting their feeding and breeding.  Developments in lighting technology have led to major increases in the distribution and intensity of artificial light in the past few decades and its growth is continuing largely unchecked.  When we consider why insect populations have been so severely reduced, impacting also on the populations of the bird species that feed on them, we tend to think (quite rightly) about pesticides but maybe artificial lighting is also an important contributory factor. 

Thanks to Kenny Boyle for bringing the birds at the church to our attention.

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