Learning to Count Harlequin Ducks

A flourishing ecosystem allows diverse wildlife to thrive within Glacier National Park. Glacier’s pristine mountain streams are the ideal breeding habitat for harlequin ducks, a waterbird that thrives in fast-flowing, cold streams where they breed and raise their young. Harlequin ducks are listed as a “species of concern” in Montana due to population decline and habitat loss. However, population monitoring can be challenging due to the difficulty of accessing the remote locations these birds inhabit. The Glacier National Park Conservancy is proud to support the improvement of survey methods so that researchers can better understand which locations are most practical for studying harlequin ducks.

Male and female harlequin ducks in Glacier National Park, photographed by Jake Bramante. 

With the support of Conservancy donors, former Glacier National Park wildlife technician Holli Holmes spent several seasons evaluating the effectiveness of different sampling procedures for detecting harlequin ducks in mountain streams. Holmes assessed three methods: 

• Ground-based foot surveys: Involve a team of two observers, walking along the edge of a stream looking for signs of harlequin ducks.
• EDNA collection: As organisms move through an aquatic habitat, they leave behind a trail of shed cells, skin, waste, mucus, and feathers. Just a few drops of water can contain the DNA of many different species in the area.
• Camera traps:One time-lapse and one motion detection camera are placed along the stream for every mile of a surveyed zone. The footage is then reviewed for signs of harlequin ducks.

Harlequin ducks survey in the McDonald Creek.

In 2022 and 2023, Holmes collaborated with state and federal agencies in Montana, Idaho, and Wyoming to test the effectiveness of each sampling method. The team consisted of 78 people who spent a total of 2,220 hours collecting data. 

“It was a massive field effort,” reflected Holmes. “It is truly humbling to look at these numbers.”

Searching for harlequin ducks in Glacier National Park. 

The findings gave Holmes a greater understanding of the effectiveness of the surveying methods. Her data showed that combining multiple sampling methods provides the most accurate predictions of where to locate the species. Individually, the sampling methods had a low success rate; the mean likelihood of harlequin duck detection was below 50%. However, when combining ground-based surveys with eDNA sampling, the average probability increased to 98%. This shows that if data collection includes a combination of ground-based surveys, eDNA collection, and camera traps, they are almost guaranteed to observe the species if it is present.

“What was really rewarding about this is it confirmed everyone’s beliefs that only using one of the methods wasn’t the most accurate” Holmes stated. These findings allow scientists to be confident in the methods they are using to survey harlequin ducks and other waterbirds all over the world.

Harlequin ducks easily blend in with their environment, making them hard to spot. Photo by Jeff Jones. 

The second objective of Holmes’ research was to create a predictive occupancy model in order to predict the likelihood of finding harlequin ducks in an area before embarking on a survey. Holmes created the model based on historical observation data, eDNA samples, and analysis of features within established breeding habitats. The model was then used to map the probability of occupancy in streams throughout Montana and Idaho.

This impressive model will be used region-wide to help inform where to best distribute resources for surveying harlequin ducks. Biologists will now have the ability to accurately monitor population trends over time and conduct surveys in new territories that are likely to be home to harlequin ducks. Holmes’ sampling techniques will create greater confidence in the detection and research of harlequin ducks throughout the region.

This important work would not be possible without the support of Glacier National Park Conservancy donors. As habitat destruction and population loss continue to threaten harlequin ducks, Holmes’ conclusions will guide researchers in developing strategies to further protect this species.