If watching Super Size Me was enough to stop you from eating McDonald’s, once you learn where olives comes from, you’ll probably think twice about ordering that Martini. According to a report from Nature, the machinery used to gather olives in Portugal and Spain often results in unwitting birds being sucked right off their branches and killed. Over two million birds perish each year during the olive harvest.

Vanessa Mata, lead researcher at Portugal’s Research Center in Biodiversity and Genetic Resources, says, “The machinery is perfectly fine if used during the day, as birds are able to see and escape while they are operating… However, during the night they use very strong lights which confuse the birds and lead to their death as they are ‘sucked in’ by the tractor.”

Since olive-harvesting season from October to January overlaps with bird migration patterns, several types of birds are at risk, including warblers, thrushes, wagtails, robins, and finches. The Andalusian Ministry of Environment and Planning is asking for changes to the harvesting process, writing, “It’s a real problem with serious environmental repercussions that transcend the Andalusian and national geographical limits.”

Now, no one is telling you to never eat olives again, but before you order extra olives in that Martini, maybe think twice about where they may be coming from.

H/T: VICE

More like this: 8 classic bartender debates