Cartes des tendances
A new generation of eBird Trends maps, released in November 2022, provides an unprecedented fine-scale view of where bird species are increasing or decreasing. Identifying such trends is the crucial first step to begin identifying ways to reverse pervasive declines like the ones identified by the 2022 U.S. State of the Birds report and the State of the World’s Birds.
The maps of population trends for more than 500 bird species are produced by a team of data scientists at the Cornell Lab of Ornithology using bird observations submitted by citizen scientists to the Cornell Lab’s eBird program.
For the first time scientists and practitioners can see exactly where declines or increases are happening at resolutions as small as 27 x 27 km (16.7 x 16.7 miles) region, an area smaller than many counties. The eBird Trends maps can show precisely where research is urgently needed to examine drivers of population declines, as well where conservation measures appear to be working and could be replicated elsewhere.
eBird Trends maps also show changes in bird abundance during different parts of a bird’s life cycle—a critical component that until now has been missing. Seeing how bird abundance changes during different times of the year can help scientists untangle how factors on the breeding or nonbreeding grounds could affect a species.
Thanks to the power of citizen scientists around the world, data scientists at the Cornell Lab can now produce trend estimates for species outside the United States and Canada.
What are eBird Trends maps?
eBird Trends maps show where bird abundance has increased (blue), decreased (red), or where change has been uncertain (white) from 2007-2021 within a 27 x 27 km region (represented by a circle). The darker the color, the stronger the trend. The trend shows an estimate of the cumulative percent change in population size from 2007 to 2021 and does not represent annual fluctuations in populations.
Every 27 x 27 km region on the map is also scaled by an estimate of abundance based on abundance data from 2014. Circles that are larger show where more individuals of a given species occur. Hence, larger and darker red circles indicate that a larger proportion of the population is declining.
eBird Trends are produced using a statistical method designed to account for changes in where people go birding and how the identification and detection skills of birders change over time—factors that can make estimating a population trend challenging. Another novel component of eBird Trends maps is the inclusion of habitat variables that take into account the effect of habitat on population changes.
All of the eBird Trends displayed on the website have passed critical statistical tests to ensure they are robust and reliable. An important part of this process is quantifying the uncertainty of the trend estimate. Uncertainty is quantified by an 80% confidence interval. The 80% confidence interval indicates a range of values expected to contain the true (but unknown) trend that is being estimated. If an interval contains zero, then there is low confidence in the estimated direction of the trend (positive or negative). By default, circles with low confidence in the estimated direction are shown in white. However, for some applications understanding the full spatial pattern of population change can also be valuable to interpret the trends. To see the trends across all locations toggle the “Show All Trends” in the legend. To learn more about how we estimate species’ population trends, please visit the FAQs.
What can we learn from eBird Trends maps?
Detailed snapshot of population health
Chimney Swifts have lost 50% of their population since 1970 and are at risk of losing another half of their remaining population if nothing changes, according to the 2022 U.S. State of the Birds Report. eBird Trends maps show where and to what extent, these aerial insectivores have declined since 2007. Several portions of the map below are red with larger and darker red circles particularly in the Piedmont region and the Mississippi Gulf Coast (see dashed circles), as well as localized spots in several states indicating strong declines in Chimney Swift abundance.
eBird Trends present a more comprehensive snapshot of population health by allowing us to visualize changes in abundance at local scales. Areas with greater numbers of individuals (larger circles) that are also darker red mean a larger proportion of the population has experienced a decline of a greater magnitude.
Although exact causes of Chimney Swift decline are unknown, potential factors might include a concomitant decline in insect abundance and loss of suitable nesting and roosting sites as old chimneys are torn down. eBird Trends maps allow us to identify areas with the steepest declines that are being experienced by the greatest proportion of the population, allowing practitioners to easily identify where to focus efforts to identify the drivers of population change, and implement potential solutions such as creating artificial nesting and roosting structures that could bolster the breeding population.
Regional variation in detail
eBird Trends maps highlight the fact that population change is not equal throughout a species’ range. Previous population trend estimates only provided a state or regional estimate of populations, making it difficult to assess where on the landscape to examine the drivers of population changes. The new eBird Trends maps are a breakthrough for research and conservation at relevant scales.
Wood Thrush populations, for example, show large regional variation, with a patchwork of increases and decreases. The first question that comes to mind when looking at the Wood Thrush Trends map is why are they increasing in the Appalachian region but decreasing in the Mid-Atlantic and southern New England states?
Coincidentally, in the last decade, the Appalachian Mountains Joint Venture (AMJV)—a partnership of over 50 federal, state, and nonprofit organizations from Alabama and Georgia to New York—implemented forest management projects to restore the age and structural diversity of hardwood forests in the region. These conservation measures have the potential to improve populations of forest-dwelling songbirds.
Now scientists can do additional studies to determine if those conservation practices are working, and the detailed numbers provided for each region can help. In the southeastern corner of West Virginia, a quick mouse over on the maps shows that Wood Thrushes increased by 55% from 2007 to 2021. With these details scientists can compare on the ground efforts with estimates of population change. The pop-up also shows the 80% confidence interval—an upper and lower value expected to contain the true (but unknown) trend that is being estimated. Hence, in the example above, our best estimate of the trend is 55% but it could be as low as 21% and as high as 71%.
Hyper local estimates
eBird Trends provide local-scale estimates of changes in abundance at a scale that matters for conservation. In the desert Southwest, for example, the potential effects of extreme temperature, fire, rainfall, and expanding urban environments vary across the landscape. As a result, the responses of populations to these stressors are also likely to vary across the landscape.
eBird Trends maps show declines in the Mojave region for Cactus Wrens as well as other desert-dwelling species, such as Verdin and Phainopepla. Extreme temperatures due to climate change could be a culprit, as scientists at the University of California found that birds in the Mojave Desert are declining due to decreased precipitation and elevated temperatures due to climate change. The maps also indicate additional declines in the Sonoran Desert as well as a patchwork of increases and decreases in southern Arizona and into Mexico. While it’s unclear what could be causing the variation in population changes, the maps can help scientists pinpoint where to focus research.
Season specific trends
American Robins are often seen as a ubiquitous harbinger of spring, but the eBird Trends maps paint a different story of patterns of abundance especially during the winter.
During the nonbreeding season, the abundance of American Robins has declined significantly throughout, with larger declines (darker red areas) in northern California, Nebraska, Tennessee, Louisiana, Florida, North Carolina, and Virginia.
At first glance, the large swaths of red are shocking. How could it be that American Robins, which seem to be everywhere, could be declining so much throughout their range? Observing changes in abundance can be hard to see in real time, especially if changes are occurring slowly year after year. But slow declines add up and the eBird Trends maps are a real wake-up call. The declines observed during the winter highlight a need to study populations, especially in the darkest red areas.
Producing cumulative changes in abundance for different seasons is one aspect that makes this information unique. Examining trends during different parts of a species’ annual life cycle can help scientists untangle what might be causing changes in abundance because different pressures affect species on the breeding and nonbreeding season.
As the number of people participating in eBird has increased over the years, so too has our ability to predict status and trends of species around the globe. Thanks to the global participation in eBird, we can now visualize changes in abundance for species outside the United States and Canada.
The Rufous-collared Sparrow is a common sparrow found in lowland and montane scrub from southern Mexico through Central America to the tip of South America. Thanks to eBirders the new Trends maps show changes in abundance from 2007-2021 within 27 x 27 km regions throughout most, but not all of the sparrow’s range. The light gray background shows the full range of the species, including areas where there was not enough data to reliably produce trend estimates.
In the Andes of South America, observations of Rufous-collared Sparrows were robust enough to allow for trends analysis. In this region, we see numerous red circles indicating a declining trend, with fewer white circles indicating model uncertainty. As we move southward through the range of the Rufous-collared Sparrow, more light gray shading is visible indicating lack of data and more white circles appear indicating uncertainty in the direction of the trend. Model uncertainty stems from a variety of factors, but can also indicate that additional observations are needed.
By default, circles where there is low confidence in the estimated direction of population change are shown in white. However, for some applications understanding the full spatial pattern of population change can also be valuable to interpret the trends. To see the trends across all locations toggle the “Show All Trends” in the legend.
How do I find species with eBird Trends maps?
eBird Trends maps bring the data front and center—all you need to do is pick a species for which eBird Trends are available.
From the eBird Status and Trends homepage, click on the green explore button. Next tap the down arrow next to the word “Filter” and then click the “Species with trends” box under filter by map types. Click on the photo of any species to see eBird Trends as well as weekly abundance visualizations and range maps. You can easily move between Abundance, Weekly, Trends, and Range visualizations using the menu at the top.
Click on the map and scroll to zoom in and out or use the + or – buttons on the left side of the map. To see eBird trend estimates for each 27 x 27 km circle place the mouse over the circle. The pop-up shows the median trend with upper and lower 80% confidence bounds and the average relative abundance for that species in 2014.