A project of

Blackpoll Warbler

Champion Migrant - Alarming Trends

Blackpoll Warblers are renowned for their migratory prowess, but they may be declining faster than any other land bird species in North America. One of the most common birds of the boreal forest, recent years have seen substantial declines in their numbers.

The State of Blackpoll Warblers

Northeastern United States: Rapid decline

Mountain Birdwatch data indicate a steep overall population decline (-5.1% per year, 95% credible interval = -6.0% to -4.2%) in the mountains of our region; this trend equates to a 34.2% decline (95% credible interval = 28.8% to 39.1%) between 2011 and 2019. The steepest declines were observed in Maine (see table below). These declines are in broad agreement with the USGS Breeding Bird Survey annual trend estimate (-5.8%) for our region.

The annual estimate of Blackpoll Warblers immediately surrounding ~750 Mountain Birdwatch survey locations. Vertical bars represent 95% Bayesian credible intervals (a measure of uncertainty).

Mean annual population trends (below) for Blackpoll Warbler from 2011 through 2019. A red dot indicates strong evidence for a negative trend. A trend of -2%, for example, indicates that the number of Blackpoll Warblers in our study area has declined by an average of 2% each year from 2011 through 2019.
RegionMean annual trend (%)95% credible interval
All regions combined -5.1(-6.01, -4.15)
New York (state) -4.19(-5.62, -2.72)
New York (Catskills) -5.70(-7.39, -3.84)
New York (Adirondacks) -3.59(-5.42, -1.73)
Vermont -5.51(-7.07, -3.85)
New Hampshire -4.23(-5.41, -3.01)
Maine -7.13(-8.77, -5.45)

Globally: Likely declining

Overall, Blackpoll Warbler appears to have been declining in numbers for many decades. Data collected by the USGS Breeding Bird Survey indicate large declines (>5% per year) in the number of Blackpoll Warblers counted across Canada (where most of the population lives), especially between 1970 and 1990. This species is very difficult to monitor in Canada, however, because its core breeding habitat is so remote and inaccessible. As such, confidence in these estimates is low.

Blackpoll Warbler numbers have declined across Canada according to results from the Breeding Bird Survey. However, uncertainty in these estimates is quite high and confidence low as to the exact magnitude of the decline. Figure provided by Environment Canada.

Opportunities for Conservation

The relationships between Blackpoll Warbler abundance and elevation and latitude. Blackpoll Warbler abundance increases steadily with latitude, becoming most abundant in northern Maine. Blackpoll Warbler abundance is lowest at low elevations (for example, around 600 meters) and reaches its peak around 1200 meters.

In the northeastern U.S., Blackpoll Warblers are most abundant between 1100 and 1300 meters (left panel), and at northern latitudes (right panel). The dark lines represent the mean relationship between abundance and elevation or latitude; the lighter colored-areas represent the uncertainty of the mean response (i.e., the 95% Bayesian credible intervals).

Scientists have not studied Blackpoll Warblers sufficiently to understand where and how to target conservation interventions, and we do not know why their populations are likely declining so rapidly. By attaching miniature light-level geolocators to adult Blackpoll Warblers from Alaska to Vermont, we now have good documentation of their spectacular migration routes. We do not, however, understand where the limiting factors occur during the annual cycle of this species. Has fledgling production on the breeding grounds declined? Is their long migration a particularly hazardous life period? Is deforestation and habitat degradation on the wintering grounds driving these declines? Blackpoll Warbler’s preference for high-elevation breeding habitat in the northeastern U.S. clearly put this species long-term existence at risk from global climate change. Under most climate change scenarios, Blackpoll Warbler ranges are predicted to move steadily northward and to disappear from New England by the end of this century.

Mountain Birdwatch is the only monitoring program that rigorously tracks Blackpoll Warbler populations, and it will likely play a crucial role in our understanding of this species in the northeastern U.S. Indeed, recent research (manuscript in prep) by Jason Hill suggests that Blackpoll Warbler are already responding to climate change, and that their populations in the northeastern U.S. have significantly tracked upslope by more than 50 m from 2011 to 2019. Clearly, more research is needed, and quickly, to identify effective conservation and management strategies for this species.

State of Mountain Birds