To some travelers, feeding stingrays in their native habitat may seem like a way fun to share some inter-species goodwill, but it turns out that it can leave the wildlife feeling a little off-kilter, to say the least.

According to recent announcement, a study by the Guy Harvey Research Institute, at Florida’s Nova Southeastern University, looked at how regular human interaction is affecting the marine wildlife at Stingray City in the Cayman Islands, where travelers can pet, feed and swim with the big fish. Researchers found some distinct changes in the stingrays' behavior. For instance, the fish shifted from foraging for food at night to doing so only during the day—perhaps when human visitors might be handing out snacks—and then sleeping at night.

They also became more social. Stingrays tend to be solitary, but this group began sticking together, with some oddly predictable consequences: They started getting more aggressive with each other—biting more frequently than wild stingrays—and the females started turning up pregnant year round, instead of during the traditional mating period. “We saw some very clear and very prominent behavioral changes, and were surprised by how these large animals had essentially become homebodies in a tiny area," according to a statement from study co-author Mahmood Shivji, a professor at the NSU Oceanographic Center.

The good news: Stingrays went back to their regular foraging habits during lulls in tourist traffic, so they seem not to be completely dependent on the free, human-supplied buffet, although, now with a few more mouths to feed.