What looked like a growing oil spill in Michigan’s Mackinac Straits area turned out to be a massive gathering of tens of thousands of ducks and other aquatic birds.

On December 21 of last year, the Mackinac Bridge Authority started receiving calls from concerned divers regarding a possible oil spill in the area. With each passing day, the number of calls regarding the oil spill kept growing, which makes sense, considering that the black mass that had formed on the water appeared to be growing. However, it wasn’t oil, but a record-setting gathering of Redhead ducks. In the beginning, authorities counted around 7,000 of them gathered together under and around Mackinac Bridge. Their number has grown since then, and there are now several tens of thousands of birds making up the “oil spill”.

Photo: Steve Baker/Facebook

According to Fox 2 Detroit, authorities kept telling concerned callers not to worry about the oil slicks they were trying to report, explaining to them that it was just an unusually-large gathering of birds, but many of them didn’t seem convinced. To be fair, the black mass does look very different from afar.

A Michigan bird watcher who managed to click some photos of the massive bird congregation this week estimated their number to be around 25,000 and growing. Apparently, such gatherings are normal, as the ducks prepare to migrate to the Gulf of Mexico for the winter.

The ducks aren’t expected to stay together for too long; as soon as the ice hits, they will start heading toward Mexico, but until then, there’s safety in numbers…

“If you’re surrounded by a couple of thousand other ones like you, your odds are pretty good that you’re gonna get away if an eagle comes out here,” bird counter Steve Baker told The Detroit Free Press.