At least Marks and Spencer's olive oil is not produced by the night time vacuum harvesting method which kills millions of birds. A number of newspapers reported on this last month:-
"Every year, millions of songbirds are brutally killed by suction olive harvesters as they rest at night in olive trees. In many regions, this industrialised slaughter takes place because harvesters have switched to night time harvesting simply to improve the flavour of the olives"
Apparently the colder night time temperatures better preserve the flavour. In the daytime the birds can fly away, but at night they are trapped.
"Ethical Consumer are currently looking into the best brands to buy if you want to be assured that your olive oil has not contributed to the slaughter of wild birds. Whilst the full report is still in progress, they have released the following statement to help concerned buyers in the meantime:
"In response to queries, Ethical Consumer magazine has been contacting brands about what their policy is relating to birds and olive oil. The following brands have replied to say that they do not use the olive harvesting method that leads to vast bird deaths: BionaOrganic, Mr Organic, Marks and Spencer. A more detailed report from one of their researchers is soon to come."
From the Olive Oil Times
Martin Harper, the RSPB’s director of conservation said, “Numbers of farmland birds in Europe have plummeted by 55 per cent over the last three decades and this is another shocking example of how modern agricultural practices are impacting our bird populations, including some UK species passing through the region.”
Andalusian officials have recommended the practice stops but unless legislation is passed in the next few months the “massacre” will start again in October, researchers warn.