Evening Grosbeak Population Fluctuations
Although we hear from a few participants each year who see these bright winter finches for the first time, we more frequently hear participants ask, “Where have the Evening Grosbeaks gone?”
In some parts of the continent, changes in Evening Grosbeak populations are fairly well documented. For example, in Quebec, Canada, Evening Grosbeaks were unknown, even as winter visitors, until the 1890s. The first evidence of Evening Grosbeaks nesting in Quebec wasn’t discovered until the 1940s. Their appearance was part of a gradual expansion of the grosbeak’s range from western to eastern North America. It’s thought that the planting of box elder trees (a tree related to maples and a favorite winter food of grosbeaks) enticed birds eastward or that spruce budworm outbreaks provided the food supply needed for the expansion.
In the last two decades, however, Evening Grosbeaks have become less common throughout their range. With the help of long-term data from FeederWatch, scientists are able to document the extent of declines and to map the changes in distribution of wintering populations. The map below shows the decline in the distribution and abundance of Evening Grosbeak reports. In most geographical regions, the probability of seeing grosbeaks during winter declined–and the downward trends continue. While the pattern is clear, the potential causes of the declines are murky at best. Very little is known about reproductive success or survival in grosbeaks. We do know that Evening Grosbeaks are susceptible to various diseases (including the bacterium that causes the House Finch Eye Disease), but the impacts of disease on grosbeak population numbers are unknown.
Data collected over many years by the same FeederWatchers at the same sites provide the strongest evidence for changes in distribution or abundance of wintering species. The commitment of all long-term FeederWatchers to counting birds every winter makes results like this Evening Grosbeak map possible.
Changes in the abundance and distribution of grosbeaks
The 2007-08 issue of Winter Bird Highlights reports on dramatic declines in Evening Grosbeak populations.
In the May 2008 issue of The Condor, Cornell Lab of Ornithology researchers published an article documenting that decline.
A feature article in Birder’s World magazine (now BirdWatching magazine), highlighted the research as well as a few specific FeederWatch participant observations.
A summary of the research was posted on our blog in 2011.
Learn more about the Evening Grosbeak and see a map showing the normal range of this irruptive finch.