"We decided to come closer to see what is happening," Alexander says by email.
The brothers, both photographers, discovered two mute swans struggling in the water, their necks desperately entangled.
Surprisingly, the birds paddled over and allowed Alexander to gingerly separate their entwined necks and wings. Meanwhile, Vitaly filmed the rescue, which took place in 2009 but has only recently gone viral on Facebook and on YouTube.
"Honestly, I was really surprised when [the] swan [swam] to my feet, like he heard and [understood] what I was saying," Alexander says. (See National Geographic's waterfowl pictures.)
"I thought only not to break anything. Because everything is white, it took some time to figure out" which wing belonged to which bird, he says.
This feel-good swan story raises the question—how did the birds get into such an unusual predicament, and how common is it?
The swans were most likely males that became twisted together while battling over territory, Brian K. Schmidt, a bird expert at the Smithsonian's National Museum of Natural History in Washington, D.C., says by email.
"The males typically fight to protect their breeding territory from intruding swans trying to usurp the territory. Both sexes can exhibit aggressive behavior, [but] it is most likely and intense with males," he says. (Related: "5 of Nature's Wildest Animal Showdowns.")
"This is the first time I have seen this, but I'm sure it does happen on occasion. [It's] similar to deer getting their antlers entangled."
The swans' neck fighting, coupled with hitting each other, caused them to get stuck.
Mute swan battles are rarely fatal but can be quite violent, nonetheless.
"If the intruder doesn't back down, it goes to a face-off with the birds striking each other with their wings and entangling their necks and biting each other," he says. ("Watch: Kickboxing Kangaroos and 4 of Nature's Most Impressive Fighters.")
"Most fights end here as usually the territorial male ... is better at this, and the intruder retreats."
Wary of Humans
While the idea of swans swimming to humans for help with their problem appeals to our emotional side, Schmidt says it's highly unlikely—and the swans' movement was either random or actually an attempt to drive the brothers away.
Mute swans on their breeding grounds will try to scare off human intruders, he notes. Generally, wild birds are afraid of humans and avoid them.
"These particular swans were exhausted from fighting and being entangled. As you notice in the video, both birds tried to get away from their rescuers as soon as possible," Schmidt says. (Also see "Watch a Tortoise Rescue Another in Distress—Was It Trying to Help?")
"The man was smart to be very tentative with his efforts to free them, as they could have easily bitten him."
"Right Place in the Right Time"
Nevertheless, Schmidt says the Drozdovs' intervention saved the animals' lives.
"Given how much they were [stuck together], I would have guessed they would have eventually drowned or starved if these people hadn't found them."
For his part, Alexander, who describes himself and Vitaly as naturalists passionate about wildlife photography, was glad he could help.
"We [were] really happy to be in the right place in the right time," he says.
Elena Sheveiko contributed additional reporting to this story.
Follow Stefan Sirucek on Twitter.