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Project FeederWatch
participants sometimes call or write to ask where the Evening Grosbeaks have gone or to
report seeing them for the first time. For example during the 2000-2001 winter, Carol
Harrell from Albuquerque, New Mexico wrote on her Project FeederWatch Comment Form,
"I've been living at this address since 1976, and on December 15, 1996 I saw Evening
Grosbeaks for the very first time. Now, 4 years later, they're here again! I wonder when
I'll see them next and why." 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 in Quebec. With the help of long-term
FeederWatchers, scientists are able to document whether species like the Evening Grosbeak
are undergoing range-wide or regional declines and to map the changes in distribution of
wintering populations.
Using data from FeederWatchers who
have submitted counts for at least five years, in 2003 we statistically determined the
change in probability of seeing Evening Grosbeaks for each of these observers. The map
below shows the average change in the likelihood of seeing Evening Grosbeaks in various
parts of North America in mid-winter (December to February) from 1999-2003. In most
geographical regions, the probability of seeing grosbeaks during winter has declined.
While the pattern is clear, we cannot determine the cause from our data. Evening Grosbeaks
are irruptive migrants--meaning their migration is irregular and often in response to food
availability--thus, declining observations could mean that the birds are changing their
wintering locations or that there are real declines in abundance.
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.
 Probability
of seeing Evening Grosbeaks
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| Key The colors indicate the following changes in
probability of observing Evening Grosbeaks for the years 1999 to 2003:
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