“Wow, loon chicks and ducklings sure look alike!” Evelyn remarked upon returning from Long Lake two weeks ago. Elaina, a veteran assistant who has seen a lot of both, thought this statement a bit odd, but was not terribly surprised. The chicks of loons do look somewhat like ducklings. Both are duck-shaped and downy, quite unlike adults of their respective species. And after all, Evelyn had never laid eyes on a loon chick before.

Ten days passed, and it was Elaina‘s turn to visit Long Lake. She was stunned to find the female slowly swimming about with a young mallard duckling on its back, and she took these cool photos to document her observations. The female, Elaina noted, acted as loon parents always do: she nervously guarded her small passenger, scanning the skies for bald eagles and peering underneath the water at intervals for large snapping turtles and muskies. The nearby male too behaved normally. Like his mate, he was vigilant, but he also caught tiny fish, carried them to the duckling on his mate’s back, and attempted to feed it, just as he had his own chick last year. His efforts were in vain; the duckling refused all food.

Many questions leap to mind here. 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?

The first question is the easiest. Loons and mallards are both common on our study lakes. They encounter each other all the time. But the usual result of such encounters is starkly different from what Evelyn and Elaina observed. For their part, mallard ducklings swim about with their many siblings in a large, tight, comical flotilla behind their mother. Loons often stalk these flotillas, causing the mallard female to rush her offspring to the nearest shoreline. Loons occasionally attack and kill ducklings, but do not eat them (to our knowledge). The usual nature of loon and mallard interactions, in other words, is a far cry from what Evelyn and Elaina observed.

The second question — what the loons are doing adopting a duckling – is the most vexing. Yet we have insights that permit us to reconstruct some parts of the story. The shape, size, and number of eggshell fragments in a loon nest tells us the fate of a nesting attempt. When I visited Long on 13 May, the pair had just started nesting, so we expected a hatch on 10 or 11 June. Indeed, Evelyn noted many small fragments on Long on June 14th—- a clear sign of a successful hatch. So we know that the Long pair did hatch an egg —- a loon egg — about two weeks ago. Loon pairs provide extensive parental care for their young, of course, and are hormonally primed to do so. Without question, then, the Long pair had high levels of prolactin in their blood in mid-June, as they began to care for their own chick. The rest of what occurred to bring about this most unlikely association is open to speculation. Perhaps a tiny duckling, the last to hatch in its brood, was left behind by its mother and siblings. Maybe the duckling became separated from its mother and siblings following an eagle attack. In any event, the tiny waif was likely discovered by the loon pair just after they had lost their chick and were predisposed to find and care for anything that even remotely resembled a newly-hatched loon.

Classical studies of animal behavior help us answer the question of how the duckling would accept loons as its parents. Ducks (like chickens and many other precocial birds) have a well-known capacity to imprint on the first large, moving, animal-like object they encounter after hatching. This instinct makes sense, because that object is almost always their mother or father. Imprinting helps them fixate and remain near their protector at all times. But a duckling hatching after its sibs had left would not have had a chance to imprint on any object. So it is conceivable that such a duckling might see and latch onto a loon pair. If ducklings accept humans as parents, they should easily accept loons.

Can a loon pair provide enough nourishment and feeding opportunities to allow a duckling to survive to fledging? We shall see. Loons have adopted ducklings before. A published study from the late 70s reported adoption of five eider ducklings by a pair of Arctic loons, and I reported a few years back on a pair of common loons in British Columbia that adopted a common goldeneye duckling. In both cases, the ducklings were known to have survived for many weeks in the care of their foster parents. But a mallard is a dabbling duck, not a diving duck, like an eider and a goldeneye. Mallard ducklings normally feed themselves on a variety of invertebrates and plant matter found on shorelines and in shallow water — not fishes provided by a parent bird. Despite the seeming disconnect between loons and mallards in diet and mode of feeding, Elaina’s photos show an alert, healthy-looking young mallard. Since we know the loons have been parenting the duckling for at least ten days, we must conclude that the youngster is receiving substantial nourishment by some means. So perhaps loons can keep a mallard duckling alive.

In short, we know bits and pieces of the story of how a pair of loons came to care for a mallard duckling. Much regarding this series of unlikely events remains shrouded in mystery. Even in our considerable ignorance, though, it is impossible not to marvel at this charming spectacle.