Supersized study: citizen science finds grebe that some feared losing

Aug 6th, 2013 @ 02:17 pm › Caren Cooper


There are many ways to be uppity in today’s world: stand up, step up, cowboy up, get fired up, stirred up, or simply wake up. Now consider a new one: scaling up.

In a recent paper in PLOS ONE, part of the new PLOS Ecological Impacts of Climate Change Collection, Scott Wilson and colleagues scaled up their research through the use of citizen science so that they could investigate the whereabouts of Western and Clark’s Grebes, two similar, large aquatic bird species.

Courtship for the Western and Clark’s Grebes is like synchronized swimming. The dress is black-and-white ballroom attire. They mirror each other’s graceful moves. And for an encore, they run across the water side-by-side. Unlike songbirds, they don’t care for melodious serenades or colorful feathers. They form pair bonds by getting in step with the best partner to get down and boogie. What perceptive and responsive couples they must be!


But, can they stay in sync with a changing aquatic environment? Drastic declines from the core of their wintering grounds in the Salish Sea, a network of waterways in southern British Columbia and northern Washington, suggests they cannot.

Their drop in numbers at the hub of their winter stomping floating grounds has been so sharp over the past three decades that there were calls for assigning endangered-species status.

The ominous question looms up. Are we in danger of losing Western and Clark’s Grebes forever?

Or could the core of their range change entirely? If so, where did they go?

Climate Change? Yes, No, Maybe

The need to uncover the fate of the Western and Clark’s Grebe was a call for citizen science to accomplish what a single scientist (or even a team of scientists) could not accomplish alone: investigation at the scale of species’ full global distributions.

If you know a bird watcher (and odds are that you do because 1 in 4 Americans watch birds), then you know that they like to recount what they’ve seen. That familiar trait of sharing bird experiences, quite pleasant over the first cup of tea, a bit tiring over the second, is at the heart of why we can keep tabs on the population numbers of Western and Clark’s Grebes.

In 1900, a pastime known as the Christmas Side Hunt officially transformed into the Christmas Bird Census. People began collective efforts to count as many birds as possible instead of competing to kill as many birds as possible. Now a holiday tradition for thousands of birders, the Audubon Christmas Bird Count has amassed millions of observations. These records can be pieced together to examine population trends and distributions shifts over time for hundreds of species across the U.S.

Sounds simple, but successfully using citizen science data is rarely easy. To address potential sources of bias in long-term citizen science data, the authors applied hierarchical Bayesian models and evaluated and addressed as many assumptions as possible.

The first hurdle was species identification. Western and Clark’s Grebes were considered one-and-the-same species until 1985. At that point, taxonomists decided that Western Grebes were actually two species: Western Grebes and Clark’s Grebes. Clark’s Grebes have never been very common. For the purposes of this study, the solution was to lump these species and examine patterns of Aechmophorus spp.

Other complications included varying observer effort and varying modes of transportation (foot, boat, and car) by participants in the Christmas Bird Count over the years. It is nontrivial, but essential, to deal with the lack of sampling consistency across the 163 census areas over 36 years that resulted in 2,478,449 observations of Aechmophorus spp.

Yet another complication was that each census area of the Christmas Bird Count, like most study sites, were not placed randomly in the landscape. For example, there were only there census areas in Baja, California, which raised the question, “could more grebes be “hiding” there?” Nor were all the Christmas Bird Count census areas established at the same time. Half had been surveyed for the entire 36 years included in the study, but the remaining half lacked surveys for some of those years.

After careful analysis, what did Wilson and colleagues find?

Continent-wide, the population of Aechmophorus grebes have declined by 52% between 1975 and 2010. That’s an annual rate of 2%. They declined by 95% in the Salish Sea as it went from hot spot to vacant spot. At the same time, grebes increased by over 300% in areas where they were previously sparse, such as in southern California and northern Mexico, interior California and Nevada. Consequently, the center of the species winter distribution has shifted south by almost 900km!

We hear a lot about global climate change, but there are other types of global changes, including oceanic change. Marine birds are at risks from by-catch in line and gillnet fisheries, pollution, overharvested fish stocks, oceanic regime shifts, periodic changes in sea-surface temperatures, and thermocline and nutrient upwellings that cause cascading effects.

The authors played it cool, making no suggestions about a possible role of global warming. They do not know why Aechmophorus grebes have declined overall nor why their range has shifted so dramatically.

The authors suspect dramatic changes in the abundance of sardines and herring are the immediate cause. But with so many changes going on, it is hard to point to one particular cause without further study.

Environmental problems have scaled up to global levels, and so must research. The population crash in the Salish Sea was not representative of the entire range. By scaling up, and dealing with the challenging hiccups of historic data, the authors provided a comprehensive picture. Now with a little hurrying up and owning up, we can find and remedy the root causes of these types of changes.

First photo: Western Grebes courtship display by Mark L. Watson on Flickr

Second photo: Western Grebes running across water by Teddy Llovet on Flickr



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