By Rémi Torrenta, BC Projects Coordinator, Birds Canada
The BC Coastal Waterbird Survey is one of the most popular volunteer monitoring programs we offer in British Columbia. It’s fairly simple: volunteer birders are assigned to a specific shoreline, and every month they walk their shoreline and count all the waterbirds and raptors they detect, either inland, nearshore or offshore. This program is extremely important as it allows us to identify waterbird population changes on the BC coasts, and investigate causes which informs our conservation work.
Five years ago, we published the results of the trend analysis using 20 years of data from the BC Coastal Waterbird Survey, in the scientific journal Avian Conservation and Ecology. This year we were celebrating the quarter-century anniversary of the BC Coastal Waterbird Survey! We updated our population trend models and analyzed data collected by our amazing volunteers between 1999 and 2025. Technically, this is a 26-year trend analysis, but with a one-year gap during Covid we are actually analyzing 25 years of data. A trend analysis simply means we look at how bird populations have changed over time—whether they’re increasing, decreasing, or staying stable.
In this new trend analysis, we use updated statistical models, a process that helps us make sense of large amounts of data and predict patterns. These new models let each survey site “borrow information” from nearby sites. In simple terms, we use data from neighbouring areas, knowing that birds living there will be subjected to similar environmental conditions. Using this spatial information helps us make stronger, more reliable estimates, especially in areas where we don’t have many survey locations. This approach is especially important in marine environments, where data can be harder to collect, but conservation decisions are urgent.
An interesting way to analyze data is by grouping birds by the role they play in their ecosystem, including the food they eat. Scientifically, these groups are also called “guilds”. As in previous years, we looked at trends for different guilds based on diet (benthivores, herbivores, omnivores, piscivores) and migration strategy (local breeders, short-distance migrants, long-distance migrants). This year, we also took a closer look at geography by comparing population trends across four regions: Greater Vancouver area, Strait of Georgia, Juan de Fuca, and combined Outer Coast (West Coast of Vancouver Island, Central and North Coast of BC).
So what did we learn from this new analysis?
First, several species continue to show declines across British Columbia:
- Western Grebe is declining in every region
- Many others are declining in most regions but holding steady on the Outer Coast, including Black Scoter, Long-tailed Duck, Scaup species, Harlequin Duck, White-winged Scoter, Common Loon, Short-billed Gull, and large gulls
- Dunlin is declining everywhere except in Juan de Fuca
- Great Blue Heron is declining everywhere except in the Greater Vancouver area
Among all species, the steepest declines over the 25-year period are seen in Black Scoter, Long-tailed Duck, and Western Grebe. You can see the trend graphs for these three species below.
These graphs represent an index of abundance over time (using the maximum species count at each survey site over the winter season), from 1999 to 2025. Each curve represents the abundance trend line for each region, derived from the models. Trends for British Columbia overall appear in black with confidence intervals.
The abundance of Long-tailed Duck has been significantly and consistently decreasing everywhere in BC, except on the Outer Coast. Photo: Chantal Jacques
Hybrid Western Grebe x Clark’s Grebe. Western Grebe populations are in serious trouble in British Columbia. Photo: Frank Lin
Here are the new things we learned, compared to the previous analysis:
- 20 species are suffering from significant declines in the Greater Vancouver area specifically. This includes the following species that are overall stable in BC: American Wigeon, Common Murre, Pigeon Guillemot, Red-throated Loon, Pacific Loon.
- Surf Scoter is only significantly decreasing in the Strait of Georgia, which may indicate a shift in habitat use towards the southern waters of the Salish Sea in Washington State, as they are increasing or pretty stable there.
- Some species show increasing trends across BC, such as Black Oystercatcher, Canada Goose, and Killdeer (good news?!)
At the guild level, here are the take-home messages:
- On the Outer Coast only, all bird guilds are showing a significant increase over 25 years
- The Strait of Georgia is showing a notable decrease of benthivore species and long-distance migrants, and long-distance migrants are overall decreasing in BC
- Population trends at the guild level are hiding species-specific and local-scale patterns.
In summary, the key message is that Western Grebes, as well as the populations of several species of sea ducks are progressively disappearing from our coasts. Also, as expected, the Greater Vancouver area and Strait of Georgia require particular conservation attention. These results will continue guiding future research collaborations and conservation planning.
The importance of Coastal Waterbird Survey data does not stop here. This data is routinely used in a variety of research projects, environmental assessments, and collaborative work. For example, we are about to publish a similar waterbird population trend study, this time integrating data from both the Coastal Waterbird Survey in BC, and the Puget Sound Seabird Survey in Washington State. This study delivers the first multi-scale assessment of coastal waterbird population trends across the transboundary waters of the Salish Sea of British Columbia and Washington State.
In a recent scientific publication, we also assessed the impact of vessel traffic on waterbird populations, for 24 overwintering coastal waterbird species in the Salish Sea, using data from both programs between 2011 and 2023. Results highlight that, in all examined families, distribution overlaps to some degree with areas of high vessel density. The majority of species that are actually declining in the Salish Sea seem to show more negative occupancy trends in areas of high vessel density. This may reflect the additional pressures that the birds face in those areas, for example through reduced foraging and the higher energy cost of frequent disturbance.
For more precise details about these studies, graphs for all bird species, and more coastal waterbird research and conservation updates in British Columbia, you can have a look at our last Newsletter, the British Columbia Coast BirdWatch, at this website: https://www.birdscanada.org/bccws_newsletters
A huge thank you to Danielle Ethier and Rory Macklin for their help with the analyses, and to all our BC Coastal Waterbird Survey volunteers for making this work possible!
Finally, if you want to become a volunteer for the Coastal Waterbird Survey and contribute to data collection for this exciting program, you can email me at: rtorrenta@birdscanada.org