If it's not birds, it's cows. Over the weekend, 390 cows were being transported by Boeing 747. As the plane was somewhere over the Irish Sea, a fire alarm went off, and the pilot was forced to give a mayday call and make an unscheduled landing.

Only there wasn't a fire. It turns out that 390 cows produce a lot of heat. And gas. Which, well, you knew that already.

The International Business Times reports:

However, technicians later found no evidence of fire, and concluded that the alarms must have been tripped by heat from the cattle.

The body temperature of cows is typically 38.6C [or 101.48 F], slightly higher than that of humans. However, cows also emit 100-200 litres of methane per day, in the form of flatus. The crowded conditions, plus the presence of noxious gas emissions, may have raised the temperature on board.

At least it's less mysterious than the time that researchers found reindeer parts in the engines of a plane forced to make an emergency landing because of a bird strike. Yeah, you read that right.

[IBTimes]

Image: USDA/Public domain (Source)