After last week’s column about boreal irruptives, I received an e-mail from Mildred Bennett, who was curious about the winter finches she had seen in her yard over the years. Specifically, she commented on two of my favorite winter finches: pine grosbeaks and evening grosbeaks.

“We had never seen one until about 10 years ago. We had a pair visit for a few weeks,” Mildred wrote of the pine grosbeak. “We were both amazed at their beauty and such a soft voice for a good-sized bird.”

Mildred’s description of the pine grosbeak captured the bird perfectly. The males are striking in their dark red or russet body plumage, which contrasts sharply with their black wings and tail. Females are overall grayer, but still sport a yellowish wash of color over their heads and upper backs.

Most apt was her observation of the birds’ vocalizations. I have often thought their quiet, almost whispered call notes would be more fitting coming from a bird half their size.

More than once, I’ve observed a large flock as it devoured the fruit of a crabapple tree. The birds called softly to one another as they ate the sticky fruits, seeming to end up with more of the food sticking to their beaks than actually being consumed. They looked like people at a pie-eating contest.

Pine grosbeaks are known as an “irruptive” species. They occupy or remain near most of their breeding territories year-round. However, when there are widespread cone, berry and nut crop failures, they “irrupt” from their normal ranges in search of viable food sources.

According to Matthew Medler of the Boreal Songbird Initiative in a report written early last fall, pine grosbeaks “are making their first major irruption into the northern U.S. in several years. Initial reports were of a few individuals at a time, but pine grosbeaks are now being seen in some places in flocks of 20 to 40 birds, with several spectacular adult males mixed into these flocks.”

Currently, the Maine Bird Alert states pine grosbeaks “continue to be encountered with exceptional frequency and numbers.”

Evening grosbeaks – also an irruptive finch – have been reported statewide as well this winter. Despite this, many people have noted they seem to be less abundant than they were years ago. In fact, The National Audubon Society reports they have declined by 78 percent over the last 40 years.

Interestingly, before the mid-1800s this finch was considered to be a rare sight east of the Mississippi River. Soon after this time period, it began to make regular winter irruptions and gradually increased its range eastward, reaching its highest numbers between 1940 and 1980.

There are two factors that seem to have had the most influence in the birds’ expansion. First, the planting of box elder trees as prairie windbreaks and ornamentals provided the birds with abundant over-winter seed.

Second, periodic outbreaks of spruce budworm are thought to have provided the birds with a superabundant food source during the summer, making it easy for the birds to breed successfully and continue to expand their ranges.

The bird’s decline since the mid-1980s seems a little harder to pinpoint. The Audubon Society cites degradation of their boreal forest habitat, insecticide use, competition with other finches and the spread of disease from other finches as contributing causes.

Add to this the typical fate of many other birds – such as collisions with buildings and moving vehicles, among other things – and the toll eventually adds up.

I, like Mildred Bennett, also miss seeing this large, flashy finch and consider it a special occasion when they do happen across my path. And I’ll never forget how author Scott Weidensaul recounted a friend’s description of them: as “grospigs,” due to their amazing ability to empty a backyard bird feeder of sunflower seed in record time.

For the Audubon Society’s list of the top 20 common birds in decline, and how you can help, go to: www.audubon.org/bird/stateofthebirds/cbid/browseSpecies.php.

bdnsports@bangordailynews.net