Environmental Challenges and Reproductive Success in Harlequin Ducks

By UMBEL May 18, 2022
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Laura Whitehouse

Born epic adventurers, Montana’s Harlequin Ducks migrate latitudinally each year, between breeding sites in turbulent, glacially-fed streams of the Rocky Mountains and a wintering range on the rough, coastal waters of the Pacific Ocean. Amphibious swimming skills make these birds seem as at home below the surface as they do above. They move like fish, navigating torrential currents and feeding among rocks on the bottom. But these whitewater adventures are not always without mishap. X-rays of museum specimens reveal multiple healed fractures in the bones of adult birds, meaning that the ducks can carry out their extreme life history while nursing serious injuries. In spite of their tenacity, compared to other North American duck species, harlequins remain relatively rare. In Montana, where the population is estimated to be between 150-200 breeding pairs, Harlequin Ducks are listed as a species of concern.

Biologists in Glacier National Park (GNP) have been monitoring Harlequin Duck populations for over thirty years. Almost 25% of Montana’s breeding population, the highest density of breeding pairs in Montana, nests along the upper reaches of GNP’s McDonald Creek. Though the species is declining elsewhere in the West, the Harlequin Duck population in the park appears to be stable. Even so, surveys in 2010 revealed that the chick count was zero. Wildlife biologist Warren Hansen and his colleagues wanted to know why. In 2011 Hansen began graduate school at the University of Montana, where he and graduate advisor Dr. Creagh Breuner teamed up with park biologists, Lisa Bate and Steve Gniadek, to try to learn what factors might stymie Harlequin Duck reproductive success.

The research team built upon a Harlequin Duck dataset that dated back to the 1970s. They identified several possible stressors, including the presence of the nearby Going-to-the-Sun Road, non-optimal streamflow, and predation (by animals like red squirrels and mink). They observed the birds’ behaviors, particularly in terms of nesting success. They also measured concentrations of metabolites, or by-products of stress hormones, stored in feathers. To carry out this last measurement, they collected feathers from the tails and backs of captured ducks. Then, they fitted the birds with radio transmitters. By observing daily flight patterns, the researchers discovered that only half of the observed birds were nesting. The researchers then searched the ground for nests along the banks of MacDonald Creek, nervous work in Grizzly Bear country where most folks want to keep their heads up. They tracked timing of nest building, numbers of eggs laid, numbers of chicks hatched, and numbers of young fledged.  

Back at the lab, Hansen analyzed feathers for presence of stress metabolites. Female birds that established nests had lower concentrations of metabolites in their back feathers than the female birds that didn’t nest. Knowing when Harlequin Ducks molt their feathers can help identify causes of stress. In this case, the feathers analyzed by Hansen were grown in the spring before they migrated to breed in Montana streams. This meant that stressful circumstances did not occur on their breeding grounds, but rather, took place during harlequin’s overwintering at sea. Hansen, now the MT Fish Wildlife and Parks Region 3 Wildlife Manager, wonders if the stressful circumstance could be related to food resources; if the birds don’t get enough food—or enough of the right kind of food—in the winter, they may be less likely to breed during the following summer. Similar carryover effects between seasons have been well-documented in other bird species.

Once the data from the nesting study was analyzed, the researchers found some curious outcomes.  First, proximity to the Going-to-the-Sun Road appeared to have little influence on the birds’ behavior, although at the time of the study, the road was not yet open so there was relatively little disturbance. Still, the birds preferred quality primary habitat types. Second, egg and nest predation may have had some impact on nesting success, but further investigation is needed to determine how strong that effect might be. And third, what was clearly evident was that nesting success was negatively correlated with severe streamflow events. This is particularly relevant in a changing climate. Historically, the hydrograph on McDonald Creek has been relatively predictable over time. Water levels tend to spike in spring with the snowmelt and rain, then drop throughout the summer, reaching low flow by summer’s end. Occasionally, however, spikes in the hydrograph occur unpredictably, after the Spring peak, when harlequin ducks may have already established nest sites. Out-of-season floods can wash away nests located near the stream edge, drowning eggs and chicks. If changes in the climate cause the hydrograph to become more erratic, this could have big impacts on Harlequin Ducks’ nesting success.

These parti-colored birds have attracted the attention of concerned Montana biologists outside of Glacier National Park too. Kristina Smucker and Chris Hammond, at Montana Fish Wildlife and Parks, have also been working with GNP’s Lisa Bate on a related study conducting analysis on Harlequin Ducks that migrate between the Pacific coast and the Rocky Mountain Front. In an interagency collaborative effort with biologists from British Columbia, Alberta, Washington State, Wyoming and Montana, the team is collecting data on migration, incubation behaviors and fledging success.

Although summering in Montana is not without challenges for Harlequin Ducks, fortunately Glacier National Park and the Rocky Mountain Front remain breeding strongholds. Thanks to large-scale conservation and forethought by our nature-minded predecessors, our Montana mountains may provide a summer respite from the rough seas of winter.

To learn more about Harlequin Duck research in Glacier National Park, check out the Harlequin Ducks Resource Brief or see the articles below.

Hansen, Warren, et al. “Influence of Streamflow on Reproductive Success in a Harlequin Duck (Histrionicus histrionicus) Population in the Rocky Mountains.” Waterbirds 42.4 (2019): 411-424.

Hansen, Warren K., et al. “Feather and faecal corticosterone concentrations predict future reproductive decisions in harlequin ducks (Histrionicus histrionicus).” Conservation physiology 4.1 (2016): cow015.