Redpolls are small, energetic finches that belong to the genus Acanthis. There are two main species of redpolls that occur in North America – the Common Redpoll (Acanthis flammea) and the Hoary Redpoll (Acanthis hornemanni). Both species breed in the arctic tundra of Canada and Alaska and migrate south in the winter months, sometimes in large numbers called irruptions. But just how rare are these winter finches?
What is a redpoll?
Redpolls are in the finch family Fringillidae along with other small northern finches like pine siskins and crossbills. They are tiny birds, weighing just 10-20 grams and measuring 11-13 cm in length. Their plumage is streaked brown and white, the males having pinkish-red caps and breasts in the breeding season. Their small size and short conical beaks allow them to feed on very small seeds.
Redpolls have several adaptations that allow them to survive cold arctic winters. Their feathers are very loosely attached, allowing them to increase their insulation by up to 20% during cold weather. They can reduce their body temperature at night by several degrees Celsius to conserve energy. Redpolls also have larger muscles to generate heat and a specialized vein system in their legs to minimize heat loss.
Range and breeding habitat
Common and hoary redpolls breed across the tundra regions of Alaska, Canada, Greenland, and Iceland. Their breeding range extends farther north than any other finch species, since they are able to thrive in the extreme conditions of the arctic climate. Redpolls nest on the ground, laying 3-7 eggs in a cup nest made of grasses, moss, and feathers.
The tundra habitat allows redpolls to find food even during the short arctic summer. They mainly eat small seeds from low-growing shrubs and tundra plants like birch, willow, alder, and cotton grass. Redpolls are constantly on the move, foraging acrobatically while clinging onto bending vegetation. This tundra habitat is essential for redpoll breeding but makes up only a tiny fraction of their total range.
Winter migrations and range
As winter approaches, almost the entire redpoll population migrates south out of the arctic breeding areas. They spread across northern and central North America, as far south as northern U.S. states. Redpolls are nomadic and irregular winter migrants. Some years they move south in huge numbers in what are called irruptions, while other years they don’t migrate very far and remain in the north.
These irruptions are caused by a lack of their preferred birch and alder seed crop farther north. When food is scarce, they wander more widely searching for resources. Some irruptions have brought hundreds of thousands or even millions of redpolls to populated areas not normally part of their winter range, like southern Canada and the northern U.S. But most winters, numbers are much lower in these areas.
Common redpolls are more likely to irrupt than hoaries. However, it’s believed the hoary redpoll has a more northerly winter range across Canada and Alaska, while common redpolls occur more broadly across the northern U.S. The winter ranges of the two species overlap extensively.
Winter habitat
During the winter months, redpolls seek out habitats with catkins and other small seeds to eat. Birches, alders, and willows are preferred, but they’ll also eat seeds from conifers, weeds, and ornamental plants. Redpolls mainly eat seeds from trees and shrubs, but will supplement their diet with insects in summer.
In winter, redpolls congregate in open woodlands, thickets, weedy fields, and backyards with suitable food sources. They are highly social during winter, forming large migratory flocks of up to several hundred birds. This helps them find patchy food sources and avoid predators.
Redpolls are able to survive cold winters because their downy plumage traps heat extremely well. They reduce heat loss by fluffing out their feathers, tucking their bills into their feathers, and huddling together in cavities.
Threats and conservation status
The IUCN Red List categorizes both the common and hoary redpoll as species of Least Concern. They have extremely large breeding and wintering ranges and population sizes in the many tens of millions. Population trends appear stable, with numbers fluctuating from year to year depending on the abundance of food sources.
Redpolls face relatively few major threats. Climate change may reduce the extent of suitable tundra breeding habitat over time. Redpolls are hunted at low levels in some areas of their winter range. Collisions with buildings occasionally occur during irruptions into populated areas.
But overall, redpolls remain common and widespread finches. Their large population size and remote Arctic breeding distribution provide protection. As long as suitable winter food sources exist, their populations should remain secure.
How often do redpolls irrupt?
Redpoll irruptions are irregular and somewhat unpredictable events. They occur sporadically, often separated by years or even decades between major irruptions in a given area. For example, in a northern U.S. state like Minnesota, major redpoll irruptions might occur once every 5-10 years on average.
Some winters will see hardly any redpolls, while other winters might see many thousands passing through. There have been several notable irruptions of common redpolls in recent decades, such as in the winters of 2002-2003, 2007-2008, and 2018-2019.
It’s challenging for scientists to predict redpoll irruptions far in advance. They seem to be driven largely by unpredictable factors like seed crop failures on the breeding grounds. Often, major movements aren’t detected until the birds have already arrived in large numbers at more southerly latitudes.
How irruptions are monitored
There are several ways that ornithologists and bird watchers monitor redpoll irruption activity each winter:
- Citizen science observations: Birders submit redpoll sightings to statewide and regional online databases like eBird. A higher than normal number of reports indicates an irruption is underway.
- Banding recoveries: Redpolls banded on the breeding grounds in Alaska and Canada are occasionally recovered farther south and provide evidence of irruptions.
- Christmas Bird Counts: These annual winter bird counts help detect irruptions if counts are much higher than normal in northern states.
- Backyard feeder surveys: Project FeederWatch engages the public to track bird numbers at feeders over winter, including redpolls.
By synthesizing data from multiple sources, ornithologists can better understand redpoll movements and what drives irruptions in a given year. Certainly in any year with high numbers of redpolls, birders become excited at the chance to see these normally-northern birds.
How you can attract winter redpolls
Redpolls are sought after by many birders when they occasionally irrupt to areas south of their normal winter range. Here are some tips to improve your chances of spotting redpolls if they pass through your area:
- Stock nyger seed feeders: Nyger (also called thistle) is a tiny black seed loved by redpolls.
- Offer suet feeders: Redpolls will eat suet and peanut butter mixes, preferably in mesh bags.
- Provide water: A heated birdbath ensures redpolls have water for drinking and bathing.
- Play redpoll calls: Calling recordings may attract nearby redpolls to your yard.
- Remove house sparrows: Aggressive house sparrows can deter redpolls from feeders.
Focus on providing nyger and suet feeders with fine, small seeds that redpolls prefer. And be patient, as redpolls are nomadic and unpredictable – some winters you may not see any! But if they do show up, you’re sure to enjoy watching these energetic northern finches.
How to identify common vs. hoary redpolls
Telling apart common and hoary redpolls can be tricky, even for experienced birders. The differences are subtle, having to do with subtle plumage variations. Here’s a quick comparison guide:
Trait | Common Redpoll | Hoary Redpoll |
---|---|---|
Belly color | White to pale buff | Whiter |
Flank streaking | Heavier | Sparser |
Back color | Dark brown | Paler gray-brown |
Bill color | Blackish | More orange-yellow |
In general, hoary redpolls have paler plumage overall, with whiter underparts and less streaking. Common redpolls are browner and more heavily streaked. But the differences are subtle. Getting clear views, looking at multiple individuals, and listening for call notes will help identify them.
Relative abundance of common vs. hoary redpolls
Of the two redpoll species, common redpolls greatly outnumber hoaries across most of North America. The IUCN estimates the common redpoll global population at up to 80 million birds, while hoaries number only around 2.5 million.
During irruptions to northern U.S. states, flocks are often 90-100% common redpolls. It’s uncommon to find groups made up primarily of hoaries. However, hoary redpolls make up a larger proportion of redpoll populations in western states like Colorado and Oregon.
There seem to be geographic differences in winter abundance that are not fully understood. Banding analyses also show that commons outnumber hoaries by as much as 10 to 1 in northern wintering areas. But scientists are still studying their relative abundance and distribution as it relates to food supplies.
Are redpolls declining?
Data on redpoll populations over recent decades show no evidence that these species are declining in North America. Breeding Bird Survey trend data from 1966-2019 shows:
- Common redpoll: +0.7% per year (not statistically significant)
- Hoary redpoll: +1.6% per year (not statistically significant)
Christmas Bird Count data similarly shows no meaningful population trends for either species from 1966 to 2019. Both species do exhibit spikes during irruption years but no long-term directional changes.
Considering their remote Arctic breeding areas, large population sizes, and ability to track seed crops in winter, redpolls appear well-adapted to current conditions. While global warming may eventually reduce tundra habitat, this does not appear to have negatively impacted redpoll populations so far.
Why are redpolls associated with winter?
Redpolls have become iconic winter birds in northern regions because that is when they migrate farthest south and are most widely observed. But there are good reasons their presence coincides with the coldest months:
- Arctic breeders – Spend summer on remote tundra
- Migrate south in winter – To find food when tundra is frozen
- Irruptions linked to food – Especially birch/alder seed crops
- Form large winter flocks – To locate patchy food sources
- Well-adapted to cold – With excellent insulation from down feathers
Redpolls are able to thrive in freezing conditions that other small birds could not withstand. Their metabolic adaptations allow them to survive even the harshest winters across Canada and Alaska.
So while redpolls certainly do not breed exclusively in winter, those months provide the best opportunities to find them across more southerly latitudes. For many birders, seeing redpolls arrive at their feeders is a sure sign that winter has returned.
Conclusion
Redpolls are remarkable finches that brighten harsh northern winters with their energy and acrobatics. While common and hoary redpolls may look similar, they have different relative abundances, winter ranges, and identification features. These birds remain common but unpredictable winter migrants/visitors throughout the northern U.S. and Canada.
Irruptive migrations make redpolls less “rare” some years as they move around widely seeking food. But even in low years, their high Arctic breeding range keeps redpolls scarce across much of North America. Providing nyger seed and suet can attract them to backyards during irruption events. For many northern birders, the return of the redpolls signals an exciting start to another winter.