TORONTO -- A remarkable story of nature versus nurture played out this summer on a quiet lake in northern Wisconsin.

As chronicled by biology professor Walter Piper on the blog of The Loon Project, two loons somehow came into contact with a mallard duckling that had become separated from its family. Instead of attacking it, as most loons would, this pair decided to rear it.

“Much regarding this series of unlikely events remains shrouded in mystery,” Piper wrote June 29 in his first post about the peculiar family.

“Even in our considerable ignorance, though, it is impossible not to marvel at this charming spectacle.”

According to Piper, the unorthodox parenting arrangement was first noticed in mid-June by one of his assistants on a visit to Long Lake, where Piper’s team was keeping track of the loon couple. Another assistant visited the lake 10 days later and was amazed by what she saw.

“She was stunned to find the female slowly swimming about with a young mallard duckling on its back,” Piper wrote.

The attachment was clearly more than physical. The female loon was watching the sky and the water for potential predators, while the male loon was trying to feed the duckling with tiny fish he had caught. The duckling, like so many young fussy eaters, was refusing to eat everything that was placed in front of him, but otherwise appeared to be healthy.

This naturally raised a number of questions for Piper and his team.

“First, how on Earth did a loon pair meet up with a single mallard duckling? Second, why on earth would they adopt the duckling rather than raising their own chick or chicks? Third, why does the duckling participate in this charade? Fourth, will loons, which provide their chicks with a large fraction of their food, be able to rear a mallard duckling, which normally finds all of its own (very different) food?” Piper wrote.

Some of those questions would never be fully answered, but others would be cleared up over the next few weeks as the team started watching the family more closely.

The researchers speculate that the family was borne out of a case of perfect timing. The loons had just hatched an egg of their own and “were predisposed to find and care for anything that even remotely resembled a newly-hatched loon.” Mallard ducklings, meanwhile, tend to accept the first animal-like object they encounter as a parent – making this particular duckling, which was “facing certain death” after having been seemingly abandoned by its mother, ready to attach itself to the loons.

By July 9, when Piper posted his next update, it was clear that the loons had found a way to get around the duckling’s dietary preferences. The duckling was willing to accept the smallest of the fish the male loon gathered for it – but not any that were large enough to pose a potential choking hazard – and supplemented that by gathering some of its own food from plants near the water.

“As it turns out, there are benefits to having two parents assiduously stuffing food into you instead of one parent merely leading you to foraging areas,” Piper wrote, adding that the duckling had “matured rapidly from a tiny fuzzball into a strapping individual fast approaching adult (duck) size.”

Before long, the researchers started seeing some the duckling exhibit some loon-like behavior. While most ducklings prefer to stick to shallower water and stay above the surface, this one was occasionally diving as deep as one metre. One time, it was seen plucking a snail from the bottom of the lake, returning to the surface and eat it.

“I thought that Daffy and Donald had ruined ducks for me forever. But this little guy’s plucky adaptability might just turn me around,” Piper wrote.

A few days later, Piper was describing the trio of waterfowl as “a close-knit family, if a non-traditional one.” While the loons were still looking after the duckling and protecting it, the duckling wasn’t returning the favour – in fact, it was making it more difficult for the loons to hold onto their territory. Summer is the time of year when single loons venture out in search of mates and new territories, and existing loon couples often hide their offspring to prevent interlopers from seeing their territory as fertile breeding ground.

The mallard duckling, though, didn’t seem willing to play along with the loons’ attempts to keep it away from prying eyes. Piper described the loons’ efforts as “comically difficult,” noting one particular incident in which the family was startled by an intruder. The loons did what any loon would do in that situation, diving underwater and preparing for a fight.

“Instead of diving itself and racing underwater to hide near shore, as a loon chick would have, the duckling freaked,” Piper wrote.

“When it spotted its foster parents far away and next to nonbreeders that had landed, the duckling raced towards middle of the lake, while peeping loudly, making itself very obvious. Needless to say, efforts by the loon parents to hide their youngster were at an end.”

This summer isn’t the first time humans have discovered loons raising ducklings. Piper himself discovered a very similar situation in B.C. in 2016.

Still, the charming and unexpected levity of two loons raising a mallard duckling has brought a smile to what has otherwise been a difficult summer for The Loon Project. Piper has described it as “the worst year for chick productivity” since he started tracking Wisconsin’s loons in 1993, contributing to what he strongly suspects is an overall decline in the state’s loon population.