With Mother’s and Father’s days still fresh in mind, maybe this is an apt occasion to relate a quirky instance of parenting in loons. The topic came up abruptly last week, when Doug Giles, a lake resident in British Columbia, sent these photos. At first, I could not even
fathom what species of duckling was receiving this unanticipated caregiving. A frantic web search of ducks breeding in the vicinity revealed that this is a young Common Goldeneye. But how could such a duckling escape the watchful eye of its own mother and blunder into the path of a pair of loons?
The curious breeding behavior of goldeneye ducks provides a clue. Goldeneyes lay 7 to 10 eggs in tree cavities, and the female is the sole incubator. (Male goldeneyes leave the picture shortly after incubation begins and play no role in rearing offspring.) Goldeneye ducklings follow their mother away from the nest a few days after hatching. Unlike loons, goldeneye young feed themselves; their mother merely protects them and guides them to feeding areas where they are relatively safe from predators. The task of herding ten or so ducklings about creates logistic hurdles; ducklings commonly fall behind or lose track of their mother and siblings. When goldeneye hens converge in the process of guiding their respective broods, young intermingle, creating creches of dozens of ducklings of varying parentage. Finally, female goldeneyes, especially those with small broods, often abandon them — leaving the ducklings to fend for themselves or coalesce with broods where the female is still present.
In short, rearing of massive goldeneye broods seems haphazard and impersonal when compared with the parental behavior of common loons. If common loons are modern-day human parents in the era of small families, abundant participation awards, and kindergarten SAT prep; goldeneyes are the all-out reproducers of the pioneer days, never quite certain of how many young they have and where they all are! So we should not be surprised to encounter a misplaced or forgotten goldeneye duckling.
But why would loons adopt a young animal that differs markedly from a loon chick? First, it is important to understand that loons — like many animals — are hormonally primed to care for young. That is, young production is the crucial measure of evolutionary fitness, so we should expect all species to be committed to the rearing of young, if parental care is obligatory for survival in that species. Apparently, the drive to provide parental care is sufficiently strong that it can get misdirected at times. Among all ducks that loons might adopt, goldeneye are a good match, as they are diving ducks (not dabblers, like mallards) and subsist mainly on aquatic invertebrates and occasional small fish. Clearly this duckling is developing more of a taste for fish than is usual for its species, as Doug Giles’ first photo shows. The duckling’s willingness to accept food from another individual, moreover, shows impressive flexibility in behavior that we might not have expected.
While we can understand how the adoption of a goldeneye by loons is plausible, it is still a remarkable event. The likeliest outcome of a close brush between a small duckling and a loon pair is an attack; many ducklings are killed by loons each year. Perhaps this loon pair was primed for adoption by having lost their second chick shortly before they encountered the stray duckling.
One factor to which we definitely cannot attribute the successful adoption is relatedness between ducks and loons. Ornithologists have long known that ducks and geese are not closely related to loons. In fact, goldeneyes are cousins of turkeys and chickens, while loons are in the evolutionary lineage that includes herons, cormorants and penguins. The superficial similarity in appearance between loons and ducks results from evolutionary convergence, not common ancestry. In my view, the distant relationship between loons and goldeneyes is yet one more reason to marvel at the odd parent-offspring bond that has formed here — and hope that it leads to a good outcome.