Grosbeaks are medium-sized songbirds that belong to the finch family. They are found throughout North America and are known for their large, conical bills used for cracking hard seeds and fruits. Many grosbeak species exhibit seasonal variations in their plumage, changing color between their breeding and non-breeding seasons.
What is a grosbeak?
There are six species of grosbeaks commonly found in North America:
- Rose-breasted Grosbeak – Found in eastern North America
- Black-headed Grosbeak – Found in western North America
- Blue Grosbeak – Found in southern and central U.S.
- Evening Grosbeak – Found across northern U.S. and Canada
- Pine Grosbeak – Found across northern U.S. and Canada
- Black-backed Grosbeak – Found only in Baja California
The grosbeak’s large bill allows it to eat hard seeds and fruits that are too big or tough for smaller songbirds to open and eat. Typical grosbeak foods include sunflower seeds, berries, buds, and tree sap. Grosbeaks are medium-sized, ranging from 5.9 to 8.7 inches in length and weighing up to 3 ounces.
Do grosbeaks change color?
Many grosbeak species do indeed undergo changes in plumage color between seasons, typically developing more vivid, colorful breeding plumage in the spring/summer and duller non-breeding plumage in the fall/winter. However, the degree of seasonal color change varies by species:
Rose-breasted Grosbeak
Dramatic seasonal change – Males in breeding plumage have a bright red triangle on a white breast, black head, wings and back and white undersides. In winter, their red breast patch fades to pink and their black feathers become more brown. Females maintain similar streaked brown plumage year-round.
Evening Grosbeak
Moderate seasonal change – Males have yellow-green and black mottled plumage year-round, but their yellow-green coloration becomes more subdued in winter. Females are gray with green-yellow highlights in breeding plumage and mostly gray in winter.
Pine Grosbeak
Minimal seasonal change – Males are red overall with some yellow-olive highlights and gray wings. This coloration remains similar year-round but may become slightly duller in winter. Females are yellow-olive and gray overall, also with minimal seasonal variation.
Why do grosbeaks change color?
Seasonal color change in birds occurs due to changes in the feather structure, specifically in the types and amount of melanin pigments deposited into growing feathers. It serves different purposes depending on the species:
Camouflage
Duller non-breeding plumage provides better camouflage and avoids predator detection when the birds are not actively breeding. For example, male Rose-breasted Grosbeaks with vivid red breast patches are easier targets against snowy winter backgrounds in their breeding plumage.
Social Signaling
Brighter, bolder breeding plumage helps advertise the health and fitness of males to potential mates. In many species like the Rose-breasted Grosbeak, only high-quality males achieve the brightest breeding colors.
Territory Marking
Bolder plumage colors help males stand out and mark their breeding territories during the reproductive season. This signals “stay-out” warnings to rival males.
When do grosbeaks molt and change color?
Most grosbeaks undergo two molts per year – once after breeding and once before the next breeding season. This allows them to cycle their feathers and adopt breeding or non-breeding plumage.
Late Summer/Fall Molt
After breeding from May-July, grosbeaks will molt in late summer and early fall August-October. This replaces their bright breeding plumage with duller non-breeding colors in time for winter camouflage.
Late Winter/Spring Molt
In February-March, another molt occurs to transition back to breeding colors in preparation for courtship and mating from April-July.
Some key points about grosbeak molting:
- Molting requires a lot of energy, so their appetites increase during this time.
- The molting period is risky since new growing feathers impair flight. Grosbeaks tend to molt as a flock for protection.
- Molting is usually staggered over several weeks – not all feathers are replaced at once.
- Juveniles tend to replace all feathers during their first fall molt and adults do more gradual replacements.
How can you distinguish male vs female grosbeaks?
In most grosbeak species, males and females have distinctive plumage that makes them relatively easy to distinguish:
Species | Male Plumage | Female Plumage |
---|---|---|
Rose-breasted Grosbeak | Black head, red triangular breast patch, white undersides | Streaked brown overall with white belly |
Evening Grosbeak | Yellow-green and black mottled coloration | Gray with greenish-yellow highlights |
Blue Grosbeak | Blue overall with reddish-brown wings | Streaked brown |
However, juveniles and non-breeding adults can sometimes be harder to distinguish. In those cases, look for these subtler differences:
- Adult males are generally larger and stockier than females.
- Adult male bills often grow larger, especially in species like Evening Grosbeaks.
- Non-breeding males retain some muted or dull remnants of breeding colors.
Conclusion
Most grosbeak species exhibit some degree of seasonal color change as they cycle between breeding and non-breeding plumage. Males tend to have the brightest, boldest colors in spring and summer to attract mates and mark territories. Then drabber camouflage takes over in the fall and winter. The mechanisms and purposes behind this color change are complex, but ultimately help optimize the birds’ reproduction and survival across seasons.