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Redpoll

The redpoll (Acanthis flammea) is a small, seed-eating finch in the family Fringillidae, native to the northern boreal and arctic regions of Eurasia and North America, where it breeds in tundra, taiga, and coniferous forests before undertaking erratic, irruptive migrations southward in winter.^[1] This species is characterized by its compact size (approximately 12–14 cm in length), short conical yellow bill, red crown patch, black chin and throat patch in males, and heavily streaked brown-and-white plumage that provides camouflage in snowy habitats; variations in plumage paleness, body size, and bill length occur across its range, but these are now attributed to a chromosomal inversion rather than separate species.^[2]^[3] In a significant taxonomic update by the American Ornithological Society in 2024, the common redpoll, hoary redpoll, and lesser redpoll—previously recognized as distinct species—were lumped into the single species A. flammea based on genetic analyses revealing minimal differences and ongoing gene flow, with morphological variations explained by a supergene polymorphism.^[3] This lumping reflects advances in molecular ecology, including 2015 DNA studies and 2021 research on chromosomal inversions, which demonstrated that despite superficial differences (e.g., the hoary form's whiter, less streaked appearance and smaller size), the populations interbreed freely where ranges overlap.^[3] Redpolls are highly nomadic, with movements triggered by seed crop failures in their breeding grounds, leading to massive irruptions that can bring flocks to southern latitudes, including central North America and Europe, where they frequent weedy fields, birch catkins, and backyard feeders stocked with nyjer or thistle seeds.^[4]^[1] Behaviorally, redpolls are energetic and social, traveling in noisy flocks with a distinctive "zipping" or chattering call, and they exhibit remarkable adaptations for harsh environments, such as storing seeds in expandable esophageal pouches, tunneling into snow for insulation (enduring temperatures as low as -65°F or -54°C), and demonstrating problem-solving intelligence in experiments like the string-pulling task for food access.^[5]^[4] Their diet consists primarily of small seeds from alder, birch, and conifers, supplemented by insects during breeding; nests are woven cups of twigs and moss, often placed in shrubs or stunted trees, with clutches of 3–7 eggs incubated mainly by the female.^[1] While generally not endangered, population fluctuations tied to climate and food cycles make them a focal species for monitoring northern ecosystem health, with the oldest recorded individual surviving over seven years in the wild.^[5]

Taxonomy and Systematics

Classification History

The redpoll was originally described by Carl Linnaeus in 1758 as Fringilla flammea in the tenth edition of Systema Naturae, based on specimens from Norrland, Sweden.^[6] In 1797, German naturalist Moritz Balthasar Borkhausen resurrected the genus Acanthis (originally proposed earlier but unused) to accommodate A. flammea, distinguishing it from other finches on morphological grounds such as bill shape and plumage patterns.^[6]^[7] Historically, redpolls were recognized as multiple species within the genus Acanthis, reflecting ongoing debates in finch taxonomy that included frequent lumps and splits based on geographic variation and morphology. For much of the 20th century, up to three or more species were commonly accepted, including the Common Redpoll (A. flammea), Hoary Redpoll (A. hornemanni), and Lesser Redpoll (A. cabaret), with distinctions drawn from plumage streaking, size, and breeding ranges.^[6] These separations were influenced by earlier works like those of Sibley and Monroe (1990, 1993), but challenges in field identification and overlapping traits led to periodic revisions.^[8] Advances in molecular phylogenetics during the 2010s provided critical evidence of close relatedness within Acanthis, revealing minimal genetic divergence across forms despite phenotypic differences. Studies using mitochondrial DNA, microsatellites, and genome-wide single nucleotide polymorphisms (SNPs) demonstrated homogeneity, with no fixed differences supporting species-level separation; for instance, analyses showed shared haplotypes and low divergence rates indicative of recent common ancestry and ongoing gene flow.^[9] A key 2021 study identified a ~55-Mb chromosomal inversion (supergene) as the primary driver of morphological and plumage variation, maintaining polymorphism without reproductive isolation.^[10] These findings echoed earlier finch taxonomy shifts, such as genus-level rearrangements in Fringillidae based on DNA sequencing. This genetic evidence prompted major taxonomic revisions, culminating in the 2024 lumping of all redpoll taxa into a single species, Acanthis flammea (English name: Redpoll), by the American Ornithological Society (AOS) in its 65th Checklist supplement, citing near-identical whole-genome sequences across ranges including Greenland and Iceland.^[11] The International Ornithological Congress (IOC) World Bird List followed suit in version 14.2, emphasizing genomic homogeneity, continuous variation, and lack of isolation.^[12] As of 2025, this monotypic treatment is also adopted by BirdLife International in its taxonomic checklist, aligning with the newly established AviList consensus taxonomy.^[8]^[13]

Subspecies and Identification

The Redpoll (Acanthis flammea) is recognized as comprising five subspecies, reflecting subtle morphological and geographic variations across its range. The nominate subspecies, A. f. flammea (Eurasian Common Redpoll), serves as the baseline form with intermediate size and streaking. A. f. rostrata (Greenland Redpoll) is notably larger and heavier, adapted to coastal environments with a stouter bill for seed extraction. A. f. cabaret (Lesser or European Redpoll) is the smallest subspecies, characterized by darker plumage and more pronounced streaking on the underparts and flanks. A. f. exilipes (Siberian Redpoll) represents a paler northern form with reduced streaking, while A. f. hornemanni (Hoary or Arctic Redpoll) is the largest and palest, featuring minimal streaking and whiter underparts across high-arctic populations.^[14] Key morphological distinctions aid in separating these subspecies, though they are often clinal rather than discrete. For instance, A. f. hornemanni exhibits reduced dark streaking on the undertail coverts and a brighter white nape compared to the more streaked A. f. flammea, while A. f. cabaret shows heavier flank streaking and a smaller, finer bill than the nominate form. A. f. rostrata stands out with its deeper-based, broader bill suited to gritty coastal seeds, and A. f. exilipes displays intermediate paleness with grayer tones. These traits, including bill shape and rump streaking, provide diagnostic cues when combined.^[14] Field identification of Redpoll subspecies presents significant challenges due to extensive overlap in intermediate forms, such as "exilipes-like" birds that blur boundaries between paler and darker groups. Separating A. f. flammea from A. f. hornemanni or exilipes often requires close views or measurements, as single traits like undertail covert streaking prove unreliable amid individual variation and wear. Recommendations emphasize assessing multiple characters, including nape whiteness, overall buff vs. white underpart tones, and bill proportions, particularly in adult males where pinkish elements are more evident. Immatures and females further complicate distinctions, with genetic studies indicating clinal variation and limited differentiation supporting subspecies status despite the 2024 AOS lumping into a single species.^[14]

Physical Description

Size and Morphology

Redpolls are small, compact finches with an average length of 11.5–14 cm, a wingspan of 19–22 cm, and a mass ranging from 9–20 g.^[2]^[15]^[16] Their body structure features a rounded head, a short conical bill adapted for cracking small seeds, a relatively short and notched tail, and sturdy legs that facilitate perching in vegetation and foraging on the ground.^[17] Sexual dimorphism in size is minimal, with males averaging slightly larger than females—approximately 0.3 g heavier and with wings about 1.7 mm longer on average.^[18] Juveniles are smaller and less robust overall compared to adults, with shorter wings and lower body mass during their first months.^[18] Several morphological adaptations enhance their resilience in cold environments, including dense, fluffy plumage that insulates against extreme temperatures; individuals can increase plumage mass by approximately 31% from summer to winter, enabling survival in conditions as low as -65°F (-54°C).^[4] These variations, including in body size and bill length, are largely attributed to a supergene polymorphism involving chromosomal inversions. Bill morphology also shows subtle variation among subspecies, such as a deeper, sturdier bill in the Greenland Redpoll (A. f. rostrata) suited to processing harder seeds in its subarctic habitat.^[17]^[3]

Plumage and Coloration

Redpolls display a characteristic plumage of brownish-gray upperparts heavily streaked with dark brown, contrasting with pale underparts that are lightly streaked on the flanks and sides. Key identifying features include a small red patch on the forecrown, a black chin and throat bib, two prominent white wing bars, and, in adult males, a pinkish-red rump and undertail coverts. The bill is yellow with black feathering surrounding the base, and the tail is notched with white outer feathers.^[2]^[19] Sexual dimorphism is evident in coloration intensity: adult males exhibit brighter plumage with extensive rose-red suffusion on the breast, flanks, and rump, along with a more vivid red crown patch and bolder black bib. In contrast, adult females are duller overall, with reduced or absent pink tones, a less distinct red forecrown, and buffy-brown underparts that are more streaked. Juveniles resemble females but are even more subdued, featuring a brownish head lacking red and heavily streaked buff underparts during their initial plumage stage in summer.^[19]^[2] Redpolls undergo a complete prebasic molt following breeding, typically from July to September, replacing all feathers into a fresh basic plumage that appears slightly paler due to buff or whitish fringing on the feathers, enhancing camouflage in snowy environments. This winter plumage wears through the year, becoming darker and more contrasting by spring, though no distinct alternate plumage develops for breeding; instead, the worn basic feathers accentuate the rosy areas in males. Age-related differences persist into the formative plumage after partial preformative molt, where retained juvenile feathers create a more mottled appearance compared to the uniform definitive basic plumage of adults.^[19] For identification, redpolls show streaking on the flanks, nape, and undertail coverts, though the latter are predominantly white and less streaked in paler individuals; overall plumage tone ranges from heavily streaked brownish forms to whiter variants across their range.^[2]^[19]

Distribution and Habitat

Geographic Range

Redpolls are native to the Holarctic region, where they breed across northern latitudes from Scandinavia and Iceland in Europe, through Siberia and Asia, to North America including Alaska, Canada, and Labrador, as well as Greenland.^[1]^[8] Their breeding distribution is primarily circumpolar, with a southern limit generally around 50–60°N in Eurasia and slightly farther north in North America.^[6] Introduced populations of redpolls, primarily the subspecies A. f. cabaret, were established in New Zealand through releases from Britain between 1862 and 1875; these birds are now widespread in hill-country habitats across much of the [South Island](/page/South Island) and parts of the [North Island](/page/North Island).^[20]^[8] The subspecies A. f. flammea occupies the most extensive native range, breeding from Scandinavia eastward across northern Russia and Siberia to Alaska and northern Canada, south to approximately 50°N in Eurasia.^[6] The high-Arctic subspecies A. f. hornemanni is restricted to tundra regions including northern Greenland, [Ellesmere Island](/page/Ellesmere Island), and parts of northern Canada and Siberia.^[6] In western Europe, A. f. cabaret breeds in the British Isles, Ireland, and parts of continental Europe such as northern France to southern Norway, central Europe, and the Alps, while the larger North American form A. f. rostrata occurs in boreal zones from Alaska to Labrador. A. f. islandica breeds in Iceland.^[6] Redpolls underwent post-glacial colonization of boreal and tundra zones following the retreat of ice sheets approximately 10,000–15,000 years ago, leading to their current circumpolar distribution with genetic evidence of recent population expansions; as of 2025, there have been no reported significant range contractions.^[21]^[22] Seasonal migrations can temporarily extend their range southward into temperate zones during winter irruptions.^[23]

Habitat Preferences

Redpolls primarily occupy boreal and subarctic forests characterized by birch (Betula), alder (Alnus), willow (Salix) thickets, and conifers such as pine, spruce, and larch, as well as tundra edges with scattered shrubs.^[5]^[15] These environments provide the seed-rich catkins and understory vegetation essential for their survival, with a marked preference for open, scrubby areas over dense old-growth forests.^[24] During breeding, they favor shrubby understories or low trees in stunted boreal woodlands, particularly along river valleys where windswept conditions are moderated by vegetation cover.^[5] In winter, redpoll flocks congregate in more exposed habitats, including open birch stands, weedy fields, and woodland edges, where they exploit persistent seed sources amid variable snow cover.^[15] Redpolls utilize a broad array of semi-open country, from brushy fields and barren tundra to backyard feeders, with paler, whiter forms more common in sparser northern habitats.^[5]^[15] This seasonal shift reflects their nomadic tendencies, driven by food availability in cold, open landscapes they tolerate exceptionally well.^[25] Redpolls demonstrate key adaptations to these harsh, windswept environments, including a strong affinity for catkin-bearing trees that supply winter seeds and physiological traits enabling endurance in subzero temperatures down to -65°C.^[26]^[25] They roost in snow tunnels for insulation and use an esophageal pouch to store seeds, allowing efficient foraging in exposed areas without dense cover.^[5] In their introduced range in New Zealand, redpolls have established in analogous open woodlands, scrubby farmlands, tussock grasslands, and forest clearings featuring exotic birches and alders.^[27]^[28]

Behavior and Ecology

Breeding Biology

Redpolls typically reach breeding age at one year old.^[29] They form monogamous pairs that last for a single breeding season, with some pairs establishing bonds before arriving at breeding sites.^[30] The breeding season varies by latitude and population; northern populations breed from May to July, while southern ones may start as early as late April.^[30] In regions like interior Alaska, breeding can extend over four months, allowing for extended reproductive efforts.^[31] Nests are cup-shaped structures built primarily by the female, using fine twigs, rootlets, grasses, moss, and lichens for the outer layer, lined with feathers, fur, plant down, or wool.^[5] They measure approximately 7.5–12 cm in outer diameter and 5–10 cm deep, with an inner cup of 4.5–6 cm diameter and 3–4 cm deep.^[30] Nests are typically placed 1–3 m above ground in shrubs or conifers such as willow, alder, birch, spruce, or larch, though heights up to 5 m occur; in tundra areas, they may be lower or on the ground in rocky crevices.^[5]^[30] The female constructs the nest over 7–10 days.^[30] Clutch sizes range from 3 to 7 eggs, averaging 4–6, with larger clutches in northern latitudes and during years of abundant seed resources.^[30] Eggs are pale blue-green to turquoise, ovate, and marked with purple spots, measuring about 17 × 12 mm and weighing around 1.3 g.^[30] The female incubates the eggs for 10–12 days, beginning with the penultimate or last egg, while the male provides food to her.^[5]^[30] Both parents feed the nestlings, which fledge after 10–16 days, typically around 11–12 days.^[5]^[32] Redpolls usually produce 1–2 broods per year, though up to four have been observed in captivity; second broods may occur into August in favorable conditions.^[30] Breeding success is generally high in years with good seed crops, supporting larger clutches and higher fledging rates, but declines during poor seed years or adverse weather like cold, wet spells, when adults rely more on invertebrates.^[30] In one study of nine nests, 72% of 33 eggs hatched, with 39% of eggs resulting in fledged young.^[32]

Foraging and Diet

Redpolls primarily consume small seeds, with birch and alder catkins forming the bulk of their winter diet, comprising up to 90% in regions like southern England.^[33] They supplement this with seeds from willows, grasses, sedges, conifers such as spruce and pine, and wildflowers including buttercups and mustards.^[34] This seed-based diet supports their high metabolic rate, which enables them to tolerate extreme cold down to -54°C, with irruptive movements often triggered by fluctuations in seed availability across their range.^[33] During the breeding season, redpolls shift their diet to include a higher proportion of invertebrates for protein, with insects like aphids and spiders making up 20–30% of intake, particularly for adults in Alaska (20–25%) and nestlings in Finland (up to 90%).^[33] This seasonal change enhances nutritional quality to meet reproductive demands, though vegetable matter remains dominant year-round.^[35] Redpolls forage in flocks ranging from 10 to over 100 individuals, often numbering in the thousands during winter, allowing efficient exploitation of patchy resources.^[34] They employ acrobatic techniques, such as hanging upside down from catkins or cones to extract seeds, and frequently peck at the ground or snow for fallen items.^[33] To optimize energy use in harsh conditions, they utilize an expandable esophageal crop (throat pouch) to store up to 2 grams of seeds—about 15% of their body mass—for later digestion in sheltered locations.^[35]

Vocalizations and Communication

Redpolls produce a variety of vocalizations that serve essential roles in social interactions and territorial maintenance. The primary call types include a metallic "chit-chit-chit" or "tseet" used for contact within flocks, a sharper "pink" note as an alarm signal, and a rolling "zree" or trill delivered in flight.^[36] These calls contribute to flock cohesion, with chattering series of clipped "che" notes facilitating group coordination during foraging and movement.^[37] Additionally, a nasal, rising whistle known as the "dsooee" call is employed by perched individuals for attraction or mild alarm, while a harsher rattle ("tschrrrr") functions in territorial threats and advertising.^[37] Male redpolls deliver songs primarily during the breeding season, perching to produce twittering, warbling phrases lasting 10–20 seconds that combine elements of their calls, such as sequences of "che, che, che, tschrrrr."^[37] These songs, which can extend up to 33 seconds with around 16 notes, are more complex and frequent in males compared to females, aiding in mate attraction and territory defense.^[37] Subtle sex differences are evident, with males exhibiting greater vocal elaboration to assert dominance during breeding displays.^[15] Vocalizations vary slightly by subspecies, reflecting adaptations to different environments. The hornemanni subspecies (formerly known as the Hoary Redpoll) produces calls that are slightly higher-pitched and slower than those of the Common Redpoll forms, though overall vocal repertoires remain similar across forms and differences are subtle and not diagnostic for identification.^[38]

Migration Patterns

Redpolls are partial migrants, with northern breeding populations exhibiting irregular southward movements during winter, while some individuals remain in breeding areas if food supplies are sufficient. These movements are primarily driven by the availability of seeds, particularly from birch and alder trees, leading to nomadic behavior within their winter range. In years of abundance, redpolls may winter as far north as their breeding grounds in the Arctic tundra and boreal forests, but in scarcity, they extend south to mid-latitudes such as the northern United States and central Europe.^[39]^[4]^[40] Southward migration typically begins post-breeding in September and peaks through November, with birds traveling diurnally in flocks that can number from fewer than 100 to several thousand individuals. Return migrations northward occur from mid-March to May, though timing varies by region and weather conditions, with most departing southern Canada and the northern U.S. by early April. During winter, redpolls remain nomadic, forming large flocks—often numbering in the hundreds while foraging—that shift locations in response to depleting local seed resources.^[39]^[2]^[40] The irruptive nature of redpoll migrations follows boom-bust cycles closely tied to the abundance of birch seeds in their northern breeding areas, with major southward invasions occurring roughly every two years when crops fail. For instance, poor seed yields in boreal Canada and Alaska in 2023 prompted notable irruptions into the northern U.S. the following winter, including rare sightings along the Oregon coast. These cycles result in highly variable winter distributions, where birds move only as far south as necessary to locate adequate food, often staging short daily flights of up to 165 km.^[40]^[41]^[39] Redpolls likely navigate using visual landmarks and cues from food availability during their flock-based migrations, though specific mechanisms remain understudied. Subspecies exhibit slight differences in migratory behavior; for example, the larger Acanthis flammea rostrata, breeding in Greenland, tends to be more northerly in its winter range and initiates southward movements earlier, from late July to October, often reaching northern Europe rather than venturing as far south as nominate populations.^[39]^[42]

Conservation Status

Population Trends

The redpoll (Acanthis flammea) is classified as Least Concern by the IUCN, reflecting its extremely large global range, with an estimated 50–150 million mature individuals, though the population trend is decreasing as of the 2018 assessment.^[8] Precise figures remain preliminary due to the species' vast boreal distribution and the 2024 taxonomic lumping with the former hoary redpoll.^[8]^[5] Regionally, redpolls remain abundant across boreal zones in North America, Europe, and Asia, where they form dense breeding aggregations during favorable conditions. In North America, data from the Christmas Bird Count (CBC) indicate short-term fluctuations in counts, often influenced by irruptive migrations, but reveal no long-term decline in recent years—for instance, boreal region totals have shown variability without sustained drops since 2020.^[43] These patterns align with the species' Least Concern status, despite longer-term concerns in some areas like a reported 77% decline over 40 years in parts of North America.^[8] Population monitoring relies on citizen-science platforms such as eBird and the North American Breeding Bird Survey (BBS), which track breeding density and distribution in boreal habitats, complemented by CBC winter counts for assessing irruptive movements.^[5] In the introduced New Zealand population, established from British releases between 1862 and 1875, the species is fairly common in hill-country regions but reports indicate declines in abundance in recent years, particularly in the [North Island](/page/North Island).^[20] Fluctuations in redpoll numbers follow boom-bust cycles driven by variability in seed availability, particularly mast seeding events in boreal conifers and exposure of weed seeds under variable snow cover, leading to irruptive population shifts rather than overall declines.^[44] These dynamics ensure resilience, with no evidence of broad population crashes across the species' range.^[44]

Threats and Conservation Measures

Redpolls face several primary threats, primarily related to habitat alteration and environmental changes in their boreal and tundra breeding grounds. Logging in boreal forests disrupts the shrubby habitats of willow, birch, and alder essential for nesting and foraging, contributing to long-term population declines observed in North American surveys. Climate change poses a significant risk by altering seed availability cycles—key to their diet—and shifting breeding ranges northward; projections indicate that by 2050, the winter range may experience a 38% shift out of current areas with a 19% overall decrease in suitable area under moderate warming scenarios. During irregular irruptions southward in search of food, redpolls experience minor but notable mortality from collisions with windows in human-populated areas. Additional risks include exposure to pesticides that reduce insect prey availability, particularly during the breeding season when young redpolls rely on protein-rich insects alongside seeds. In introduced ranges such as New Zealand, where redpolls established populations in the 19th century, competition with native and other introduced species appears minimal, with the birds maintaining densities without evident negative impacts. Conservation efforts for redpolls are integrated into broader avian protections rather than species-specific programs, given their overall abundance and Least Concern status. They are safeguarded under the Migratory Bird Treaty Act in the United States and Canada, prohibiting take and promoting habitat protection. BirdLife International supports boreal forest management initiatives to mitigate logging and habitat fragmentation, while citizen science platforms like eBird enable ongoing monitoring of population trends and irruption patterns through millions of observer-submitted records. Although no dedicated recovery plans exist due to stable global numbers exceeding 50 million mature individuals, redpolls benefit from finch-focused conservation addressing shared threats like feeder-related diseases. The 2025 State of the World's Birds report by BirdLife International highlights vulnerabilities for migratory species like redpolls, emphasizing the need for enhanced climate adaptation in northern ecosystems.

References

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The "Common" form is brown and white with heavily streaked sides. Male "Common" has a rosy-red wash on the breast and upper flanks.
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Basic Description. As energetic as their electric zapping call notes would suggest, Redpolls are active foragers that travel in busy flocks.
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Redpolls are energetic little birds that forage in flocks, gleaning, fluttering, or hanging upside down in the farthest tips of tree branches.
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... resurrected genus Acanthis that had been introduced in 1797 by the German naturalist Moritz Balthasar Borkhausen. ... morphology in a Holarctic songbird".
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This small brown finch, with its red poll, belongs to a taxonomically complex group formerly consisting of three or more redpoll species.<|separator|>
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### Foraging and Diet of Common Redpoll
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[38]
Sounds and Vocal Behavior - Redpoll - Acanthis flammea
Oct 22, 2024 · Common Redpoll. Most extensive published analysis of vocalizations based on birds in Europe and Siberia (182 Zablotskaya, M. M. (1981).
[39]
Common and Hoary Redpolls - Earbirding
Jul 31, 2013 · Apparent Hoary Redpoll, eastern Ontario, 2/4/2009. Photo by ... Arctic [=Hoary] sounded clearly slower, higher-pitched and less pure ...
[40]
Movements and Migration - Redpoll - Acanthis flammea
Oct 22, 2024 · Redpolls arriving on northern Alaskan breeding grounds carried appreciable amounts of fat. However, those taken during migration periods had ...<|separator|>
[41]
Bird of the Month: Common Redpoll - NH Audubon
Feb 6, 2023 · For Common Redpolls, the drivers of the irruptions are spruce and birch seed crops in boreal Canada and Alaska where the species nests.<|separator|>
[42]
Oregon and Washington: Winter 2023–2024 - American Birding ...
A remarkable spate of at least eight Redpoll sightings in January on the Oregon Coast, where generally very rare, coincided with a cold snap throughout the ...
[43]
The Redpoll Complex - Finch Research Network
Nov 22, 2020 · The most familiar Common Redpoll (Acanthis flammea) subspecies ... The bill shape and color never looked like a good match for ssp.Missing: adaptations | Show results with:adaptations<|control11|><|separator|>
[44]
Where Have All The Birds Gone? - National Audubon Society
Curious about what the CBC data show? Audubon's Science team has built a tool where you can explore population trends over the last few decades!
[45]
Continent‐Wide Patterns of Climate and Mast Seeding Entrain ... - NIH
Feb 19, 2025 · Additionally, due to changes in snow cover dynamics, redpolls may exploit a more readily available resource—weed seeds left exposed in low snow ...