A typical method used by ecologists to predict bird populations might not be as reliable for estimating future bird counts in urban environments, which could lead to miscalculations regarding the decline of specific species.
As global bird populations decline, research from the University of Vermont reveals that some species may actually be more adaptable to changes in their habitats than previously thought, highlighting potential avenues for enhancing bird populations through urban planting initiatives. The results of this study were published in the Journal of Animal Ecology.
It has been documented that bird populations are decreasing, with nearly three billion birds lost in Canada and the United States over the past 50 years. However, tracking these population decreases is challenging, especially in the absence of consistent long-term data. This is why scientists frequently use a technique known as space-for-time substitution, which estimates future species populations based on habitat associations observed at a specific moment.
Lead author Harold Eyster, a climate scientist with the Nature Conservancy, examined breeding bird data collected from the Vancouver metro area between 1997 and 2020, along with changes in land cover using various imaging techniques and machine learning. His team discovered that overall bird populations had dropped by 26 percent, with certain species such as house sparrows, barn swallows, and starlings facing losses of up to 80 or 90 percent. The changes in land cover only partially explained these population shifts, indicating that some ecological models might be overestimating the significance of habitat relationships for birds.
Eyster, who conducted this research while a postdoctoral researcher at UVM’s Gund Institute for Environment, comments, “The data isn’t consistent. This may suggest that we should broaden the scope of some surveys we support. We are measuring one aspect—breeding birds—but we need to consider their survival year-round. Hence, we must also focus on conserving areas that will support them throughout the entire year.”
In 1997, the most prevalent bird species in metro Vancouver included the European starling, house sparrow, American crow, house finch, and violet-green swallow. By 2020, however, chickadees and bushtits had pushed swallows and sparrows out of the top five, while the northern flicker showed significant population increases. The fluctuations in bird populations did not match the predictions made through space-for-time methods, raising questions about the accuracy of estimating certain bird population losses.
Brian Beckage, a professor in UVM’s Department of Plant Biology and Computer Science and a co-author of the study, notes that these findings illustrate the complexities inherent in ecological systems. “When you create a model based on data from a single point in time, there are numerous external factors influencing the environment that you may not be fully aware of,” he explains.
For example, while large-scale environmental changes are evident, localized landscape alterations can either soften or worsen their impacts on wildlife. Here, longitudinal data becomes valuable, allowing scientists to identify the most crucial environmental relationships and understand which interventions may bolster wildlife populations during periods of significant global change.
“Longitudinal data provides insight into how these relationships evolve over time, revealing their variability and underlying factors,” Beckage adds. “This understanding helps identify when and how certain variables are significant, and how they interact with each other.”
The study, funded by Environment and Climate Change Canada, aimed to explore nature-based solutions to climate challenges, such as urban planting strategies, and their effects on bird populations in city settings. Eyster and Beckage previously found that coniferous trees may be more effective at cooling Vancouver during heatwaves, benefiting both humans and local wildlife. Moreover, planting trees offers numerous health benefits.
According to Beckage, “Planting trees can enhance environmental quality for the public; it actively combats climate change by sequestering carbon; it mitigates local climate impacts like heat by providing shade; it also creates more habitats for birds. Furthermore, it empowers people to contribute positively to their environment in various ways that aren’t overly demanding.”
Interestingly, many bird species in metro Vancouver that have experienced the sharpest population declines are considered non-native to North America. However, they tend to thrive in densely populated areas and often represent the sole wildlife interactions that urban residents encounter. Given that more than half of the world’s population resides in cities, urban areas offer crucial opportunities to foster beneficial relationships between humans and wildlife.
In 2020, Eyster conducted bird surveys in metro Vancouver that echoed studies from the ’60s and ’70s, performed outside the breeding season, and found that many avian species exhibited more adaptive and intricate behaviors than captured in traditional breeding surveys. These adaptations suggest that some birds might be more resilient to changes in land use than previously considered.
Eyster explains, “Many of our assumptions about birds are drawn from studies conducted in the early 1900s or even before. However, birds display intelligence and adaptability; they can culturally adjust. My research emphasizes the importance of being open to these changes rather than presuming birds will rely on the same resources as they did back when forests looked different.”
For instance, the Pacific Wren illustrates this adaptability. While this bird traditionally nests in extensive forest areas in British Columbia during breeding season, Eyster has observed them extending their habitat into new zones come fall and winter. “They are encroaching on residential areas, moving into people’s cedar hedgerows,” he notes. “We’ve seen a marked increase in their presence throughout urban environments.”
This shift could indicate that they are adjusting to an evolving landscape. Eyster concludes, “We need to consider not just preserving large parks, but also recognizing the significance of the entire urban landscape.”
He strongly believes that urban planners should not overlook the value of transitional areas within cities. While large forests and fields are crucial during breeding seasons, residential backyards and neighborhood greenery also serve as essential food sources, such as berries and seeds, at different times of the year.
Although climate change is often immediately blamed for bird population declines, attributing these losses solely to it is more complex. Other factors like habitat loss, fluctuations in food availability, and competition from non-native species also play significant roles.
Eyster shares his interest in researching ways to untangle the various influences at play. He believes that gaining a comprehensive understanding of the intricate relationships affecting species decline, especially those involving human interactions, is key. Urban environments may provide an ideal setting for this exploration.
The study was co-authored by Kai M.A. Chan from the University of British Columbia, Morgan E. Fletcher, an undergraduate at UVM, and Brian Beckage.
