By Rémi Torrenta, BC Projects Coordinator
Marine birds play a crucial role in indicating environmental changes caused by both natural and human factors. In a groundbreaking study spanning 29 years from 1993 to 2021, researchers have utilized large-scale beached bird monitoring program data to shed light on the mortality events of marine birds in the Northeast Pacific and Alaska. This data has helped identify the association between these mortality events and ocean-climate variability in the region. In particular, the study explores the relationship between marine bird mortality and marine heatwaves (MHWs), which are characterized by prolonged periods of significantly elevated ocean temperatures.
Data collected in the study include those from the Birds Canada British Columbia Beached Bird Survey, which began in 2002. This program could not exist without hundreds of dedicated volunteer surveyors. They follow a standardized protocol, and conduct monthly beach surveys to record bird carcasses. The resulting dataset represents the most extensive record of beached bird stranding events, both in terms of time and geographical coverage.
Buller’s Shearwater. Photo: Yousif Attia
This study is very interesting because it is the first one that reveals a clear link between bird mortality and MHWs. To summarize the results: the more likely you have a sustained sea temperature anomaly of 0.5-1°C above normal levels, the more likely you will observe massive seabird die-offs within one to six months after that ocean heatwave. The research also reveals a startling trend in the Northeast Pacific, with marine heatwaves experiencing a three-fold increase in intensity and a nine-fold increase in duration between 2000 and 2022, compared to the period from 1982 to 1999.
Some birds suffer much more than others, and that includes the auk family (seabirds that look like small penguins – murres, puffins, auklets) and the shearwater family (tubenose birds like petrels that live in the open ocean). Birds that are more generalist and that can easily switch their diet, such as gulls and cormorants, would be more resilient to MHW impacts.
It is important to mention that ocean warming is indirectly causing mass mortality among seabirds, and not directly. The exact cause of each die-off is different, but all seem to be related to warmer waters following a MHW onset, thus affecting the whole marine ecosystem. It can be either harmful algae blooms, increased disease outbreaks, or changes in the quality and abundance of prey, which can lead to starvation.
For example, in recent years and in British Columbia specifically, we observed two major die-off events: Cassin’s Auklets in 2014 (mostly died from starvation) and Rhinoceros Auklets in 2016 (mostly died from bacterial disease).
With climate change increasing the frequency and intensity of MHW, and extreme weather events (like the heat dome in British Columbia in 2021), we can expect more and more large-scale seabird mortality events, and there are concerns regarding marine bird populations’ ability to recover between these events. The mortality events documented in this study likely caused a significant reduction in the number of North Pacific marine birds. As global warming continues, the study emphasizes the potential for a reduced carrying capacity for marine birds in the Northeast Pacific.
Ancient Murrelets. Photo: Tom Middleton
Prolonged El Niño events (like the one we are currently experiencing at the moment and which will last over the next couple of years) should be more frequent and more intense in the future as a result of global warming, and will likely have harmful effects on our seabird populations. In particular, El Niño increases sea surface temperature, and reduces the upwelling of cold, nutrient-rich water that sustains diverse plankton communities which sustain large fish populations, which then sustain abundant sea birds.
The comprehensive 29-year study highlights the alarming impact of ocean warming. By understanding these trends and their consequences, we can take steps to protect marine bird populations and preserve the delicate balance of our marine ecosystems in the face of ongoing climate change.
If you want to participate in the British Columbia Beached Bird Survey and become a coastal guardian who helps detect and monitor die-offs and other issues along our west coasts (oilings, pollutions, outbreaks, etc.), you can contact Rémi Torrenta at rtorrenta@birdscanada.org. The concept is simple and anyone can take part in this survey: you walk your favorite beach every month to report and identify all the bird carcasses you found, or the absence of carcasses. We provide all the resources you need.
To read more about the study, please consult the article in Marine Ecology Progress Series.
We would like to thank all our Beached Bird Survey volunteers for their amazing involvement and dedication.
This project was undertaken with the financial support of Environment and Climate Change Canada.
