Evening Grosbeaks

The stunningly beautiful evening grosbeaks are mystery birds that come pouring from the canyons to invade our urban areas on a daily cycle- an eruptive population here in Cache Valley. I always hear their loud chirp notes high above, often beyond sight. They alight in towering trees where they feed and converse with chirps and trills all the while. Highly social, evening grosbeaks are unlike their four solitary grosbeak cousins.

Their behaviors leave me puzzled. – Why this daily ritual of flying back and forth from rural to urban? Where and when do they nest? Do they nest close together given their flock behavior? Are they urban or rural nesters? I was able to find some answers, but there are yet many gaps in on their behaviors and highly variable populations.

The Evening Grosbeaks were of much interest from the late 1800s to the mid-1900s, resulting from its eastward range expansion. Comparatively few recent studies have been conducted other than breeding ecology and behavior in Colorado during the 90’s. They were formerly restricted to the western United States but have expanded their range eastward across the country, perhaps a result of the establishment of box elder trees in eastern cities with abundant seeds that persist through the winter, and outbreaks of eastern forest insects which they feast on.

As is the case with many irruptive, nomadic species, it is difficult to determine their true population. Unfortunately, this bird has almost disappeared from the east once again, and has all but disappeared in the Appalachian Mountains and has suffered heavy declines elsewhere. A focus on understanding what is driving population trends is needed for developing conservation strategies to help it recover.

Potential causes of the Evening Grosbeak’s decline are tar sands mining, which has destroyed large swaths of its Canadian boreal forest breeding habitat. Pesticides used to control spruce budworm, an important food for Evening Grosbeak, may also be a factor. Large numbers are killed by window collisions, and cars during winter, when they gather on roadsides to pick up road salt and grit.

During the breeding season, their behavior is quite secretive, and courtship occurs without elaborate song or display. This secretiveness makes it difficult to study this species’ life history. They breed in high altitude and high latitude various forest types throughout North America. Nests are typically located high up in trees, on horizontal branches well out from the trunk. The female builds the nest, which is a loose saucer of roots and twigs lined with fine grass, moss, rootlets, needles, and lichen. Both parents, generally monogamous, help feed the young. They forage in treetops for insect larvae during the summer, buds in spring, and seeds, berries, and small fruits in winter. They sport heavy, strong beaks which can crack open the toughest shells, including cherry pits- a favorite. Evening Grosbeaks are known to snip off the twigs of Sugar Maple trees and sipping the sweet sap- yum!

As birders and citizen scientists, we must document all we can to supply the much needed dearth of data on this marvelous bird, and report it to www.ebird.org

This is Jack Greene for Bridgerland Audubon- and I’m wild about Utah and its evening grosbeaks!

Credits:

Pictures: Courtesy Pixabay, Alain
Courtesy US FWS,
Text: Jack Greene, Bridgerland Audubon Society

Additional Reading:

Evening Grosbeak, All About Birds, Cornell Lab of Ornithology, Cornell University, https://www.allaboutbirds.org/guide/Evening_Grosbeak

Evening Grosbeak, Coccothraustes vespertinus, Birdweb.com, Seattle Audubon Society, https://www.birdweb.org/birdweb/bird/evening_grosbeak

Evening Grosbeak, Coccothraustes vespertinus, eBird.org, https://ebird.org/species/evegro