A polar bear stands on an ice floe among broken sea ice

Photo: Bj Kirschhoffer / Polar Bears International

The First 40 Years: Long-Term Research in Western Hudson Bay

By Dr. Nick Lunn



17 May 2022

October 5, 2021, marked the 40th anniversary of my first trip to Churchill. On that date in 1981, I had no sooner crossed the tarmac of the old Churchill airport when I was whisked away to help in the handling of X05547, a 3-year-old subadult male captured not far from the Churchill dump. To a recent university graduate, I was amazed at being in Churchill and to be up close to an iconic predator. Little did I know where this first encounter would lead. 

At the time, I had no way of knowing that I was contributing to what would arguably become the best dataset for any population of polar bears, one that would eventually allow us to understand the link between climate warming and the well-being of polar bears across their range.

Early days

When Dr. Ian Stirling established a polar bear research program near Churchill in 1980, his goal was to answer basic and fundamental ecological questions that were applicable to polar bears across the circumpolar Arctic. Back then, global warming was not on anyone’s radar screen. 

Churchill was an ideal location to study polar bears because Hudson Bay is ice-free for three to four months each year. During that time, the bears are forced ashore, where they gather in a relatively small area. Thus, rather than try to sample bears of all age- and sex-classes out on the sea ice of Hudson Bay where they occur in lower densities, Dr. Stirling recognized that it would be much easier to do so while the bears were on land in an area that is less than one percent of the area of the Bay. Further, the logistics of operating out of Churchill, which had both air and rail service, were much more cost-effective than undertaking similar studies in the remoteness of the High Arctic.

Our research consisted of a series of studies, each lasting two to five years, to answer specific but interrelated questions. The social behavior of bears, reproductive ecology, population dynamics, and even the significance of onshore feeding were some of our earliest studies.  Answering the questions most effectively required us to handle a sample of bears to uniquely identify them, record body measurements (e.g., length, girth), assess overall health (e.g., examining tooth wear, assessing fatness), and collect various biological samples. 

Although these are relatively simple and straightforward to collect, we took great care to do so systematically and consistently, thus ensuring comparability between individual bears both within and across years. Novices were taught how to take these measurements, which were then double-checked. Nothing was left to chance. We all learned how to handle polar bears by doing, not by watching!

A mother polar bear and her two cubs peak out of their den

Photo: Dr. Steven Amstrup / Polar Bears International

Invaluable histories

Over the years, the annual handling of a sample of bears resulted in a growing database of marked individuals for which there were corresponding body measurements, health assessments, and biological samples—providing an incredible record of changes over time. Individuals handled in previous years and later recaptured told interesting stories about where and when they were encountered and when they had cubs (and how many). Over time, we started picking up independent juveniles and adults that we had first captured as cubs. 

The information gained not only provided interesting stories but also important insights into Western Hudson Bay polar bears. For example, the annual captures contained a number of independent yearling bears (21 months old), which demonstrated that, in Western Hudson Bay, mothers were able to successfully wean young a full year earlier than in most other populations.

By the end of the first two decades, we noticed that some of the measurements were changing significantly over time. In particular, we recorded reductions in the body condition of males and females, the number of cubs being produced, and the number of independent yearling bears in our capture samples. While these would be far more difficult to interpret with only three to four years of data, what we had documented over 20 years of studying Western Hudson Bay bears definitely signaled something was afoot. 

But what was changing?

Sea ice is a key component of the Arctic marine ecosystem and to the life history of polar bears—it’s the platform from which they hunt seals, mate, and travel. During the same period in which we observed changes in the Western Hudson Bay polar bears, warming temperatures and a trend towards earlier breakup of sea ice in the spring had been documented by atmospheric scientists. An analysis of the data revealed a significant relationship between the date of sea ice breakup and the condition of bears when they came ashore. Bears came ashore in poorer overall body condition in years when breakup was earlier, presumably because they had less time on the sea ice to hunt. 

One of the more striking results linking sea ice breakup to polar bear well-being was that cubs born in the winter of 1992 tended to be in better condition and have higher survival rates than cubs born in the years preceding and after. In June 1991, Mount Pinatubo, a volcano in the Philippines, erupted. Large amounts of particulates were released into the atmosphere, resulting in cooler than normal global temperatures in 1991 and 1992. Sea ice breakup in Hudson Bay was significantly delayed that year to the benefit of cubs born in 1992. This formed some of the earliest evidence that long-term research and resultant data on polar bears could pick up larger environmental signals in the Hudson Bay ecosystem.

Twin coy cubs snuggle in the snow

Photo: Dr. Steven C. Amstrup / Polar Bears International

Putting the puzzle together

Although a growing body of evidence linked human-caused greenhouse gases to global warming, it was difficult to quantify the effects on polar bears. Understanding the impacts would require large datasets on many individual bears over time. Working with colleagues from the U.S. Geological Survey, we discussed using the long-term data from Western Hudson Bay—the best-studied bears in the world— to try to better understand how polar bears would respond to a warming climate. If these data could help answer the questions, the insights could help inform other, shorter, polar bear datasets. 

Our collaboration resulted in an important finding: the data showed that the Western Hudson Bay polar bear population had declined by approximately 20% over a 20-year period. Evidence suggested that this decline was likely due to earlier breakup of sea ice and decreased survival of polar bears, particularly juveniles, subadults, and older bears.

Since these early studies, there has been a growing recognition of the value of long-term datasets, which allow one to tease apart changes that are part of the natural variation inherent in ecosystems from unidirectional changes that signal a fundamental change. 

Today, loss of habitat due to climate warming is recognized by the five Polar Bear Range States as the primary threat to the long-term persistence of polar bears. Highly specialized species, such as the polar bear, are particularly vulnerable if their environment changes. 

The Western Hudson Bay dataset now spans 40 years of research. In fact, we are now capturing descendants of some of the first bears we caught back in the early 1980s! Moving forward, this research will become increasingly important as we try to better understand how polar bears will respond to the impacts of global warming, estimate what may lie ahead for other populations not yet touched by these impacts, and provide science-based advice to help inform conservation actions.

Forty years ago, I began a journey with no idea of where it would lead. I am grateful for the opportunities that I have been given and hope that the ongoing research we have undertaken in western Hudson Bay will lead to concrete actions to conserve and secure polar bears in the wild for many future generations to come.

Dr. Nick Lunn is a research scientist for Environment and Climate Change Canada.