{"id":7787,"date":"2026-10-09T11:45:00","date_gmt":"2026-10-09T11:45:00","guid":{"rendered":"https:\/\/wordpress.viu.ca\/biol325\/?p=7787"},"modified":"2026-10-09T16:56:06","modified_gmt":"2026-10-09T16:56:06","slug":"fox-sparrow-fever","status":"publish","type":"post","link":"https:\/\/wordpress.viu.ca\/biol325\/2026\/10\/09\/fox-sparrow-fever\/","title":{"rendered":"Fox Sparrow Fever"},"content":{"rendered":"\n

What comes to mind when you hear the word sparrow? Maybe a small, ordinary brown bird, hopping around your backyard. But the fox sparrow is not your typical sparrow! With their striking variety, behaviours, and beautiful songs, these birds have captured naturalists’ attention for generations. By the end of this tribute to fox sparrows, you may find yourself appreciating these wonderful birds just as famous historical naturalist John Burroughs did in his essay A Spring Reish<\/a>, when he stated:<\/p>\n\n\n\n

\u201cThe fox sparrow, who passes earlier (sometimes in March), is also chary of the music with which he is so richly endowed.  It is not every season that I hear him, though my ear is on the alert for his strong, finely modulated whistle\u201d (Burroughs, 1896\/2010).<\/p>\n\n\n\n

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Code: FOSP <\/p>\n\n\n\n

Family: Passeriformes <\/p>\n\n\n\n

Order: Passeriformes <\/p>\n<\/div>\n\n\n\n

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Description and ID <\/p>\n\n\n\n

Weighing in at 26- 44g<\/a>, with a wingspan of 26.7- 29cm<\/a> and a length of 15- 19cm<\/a>, these chunky little sparrows will steal your heart! Fox sparrows have a robust body. They have a small and rounded head and a stout bill. In flight, their broad wings and rounded tail feathers help them sustain short but explosive bursts of flight efficiently.<\/p>\n\n\n

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(Photo by tinyfishy<\/a>, 2008)<\/figcaption><\/figure>\n<\/div>\n\n\n

What makes Fox sparrows particularity fascinating is their diverse variation in appearance. Depending on their geographical region, adult plumage ranges from a vibrant reddish color to a slate-gray, with four main groups across their range. In other words, there is almost a fox sparrow for everyone!<\/p>\n\n\n\n

The first contender is the subspecies that gave fox sparrows their name: the red or \u201ctaiga\u201d group. They display a striking \u201cfoxlike\u201d reddish coloration across its head and body, complemented with a dark gray-brown streaked crown. Their white breast and sides have the sparrow species signature chest markings; however, this species, have distinctive reddish-brown chevron shapes.<\/p>\n\n\n

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(Photo by Evan Lipton, 2017.<\/a>)<\/figcaption><\/figure>\n<\/div>\n\n\n

Next up is the “Sooty”(Pacific) subspecies. Interestingly, their breeding region affects their coloration, where farther North and West, tend to be paler. They have large brown chevrons along their breast, dark brown flanks, undertail coverts, and mantle that contrast with grey auriculars. The southern population tends to be darker overall, with subtle reddish tones appearing on the wings and tail.<\/p>\n\n\n

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(Photo by Betsy Matsubara<\/a>)<\/figcaption><\/figure>\n<\/div>\n\n\n

The Slate-colored or interior west group is next, and contrary to its simple-sounding name, it may have the most striking plumage of all! Their breasts and underparts have, dark brown chevrons, while their wings and tail can show a rich reddish coloration. In contrast, their rump, mantle and head have grey plumage. Overall, this combination creates a enticing look for a bird whose name makes it sound boring!<\/p>\n\n\n

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(Photo by Tom Benson<\/a>)<\/figcaption><\/figure>\n<\/div>\n\n\n

If you still have not chosen a favourite subspecies, this last competitor may be the one for you! Meet the Thick-billed (California) fox sparrow, known for its (you guessed it!) very thick bill. The bill is not the only characteristic that sets this sparrow apart. Unlike finches and other similar birds, fox sparrows have a distinguishable, tall gray crown. This subspecies also have reddish-brown plumage on the tails and wings. Like the other subspecies, these sparrows proudly wear the fox sparrow’s signature reddish-brown chevrons along their white breast and sides.<\/p>\n\n\n

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(Photo by Steve Rottenborn, 2018<\/a>)<\/figcaption><\/figure>\n<\/div>\n\n\n

Distribution and Habitat<\/p>\n\n\n\n

Fun fact: fox sparrows are among the most widely distributed, variable birds in North America. Each subspecies is adapted to different regions of North America, creating unique habitat preferences and migration strategies. So, think of them as four different versions of the same bird, each with its own favourite place to call home.<\/p>\n\n\n\n

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The sooty fox sparrow, a true Pacific coast specialist. Picture this: In the summer, they travel northbound to Alaska to breed in habitats consisting of willow and blackberry thickets. As winter approaches, they travel back southbound along the Pacific coast to California. British Columbia residents stay year-round because of their seasonal adaptations. However, a 2018<\/a> study on the discovered that these \u201csedentary\u201d birds traveled a total of approximately 3,000km between their breeding and wintering grounds.<\/p>\n\n\n

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(Image by David Sibley)<\/figcaption><\/figure>\n<\/div>\n\n\n

Among the four fox sparrow subspecies, the red (taiga) is the most migratory.  In winter, these birds are found across eastern North America, particularly in areas with dense forests. Their migration routes stretch across Canada and the United States, ranging from Alaska to Newfoundland. In their wintering grounds, they can be found along the forest edges surrounded by trees such as black and white spruce, balsam fir, tamarack, aspen, birch, willow and alder.<\/a><\/p>\n\n\n

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(Image by David Sibley)<\/figcaption><\/figure>\n<\/div>\n\n\n

Slate-colored fox sparrows live in the Interior West of North America, from California to New Mexico in the winter. Summer breeding occurs in central British Columbia, where they favour the riparian woods.<\/p>\n\n\n

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(Image by David Sibley)<\/figcaption><\/figure>\n<\/div>\n\n\n

Next are the Thick-billed fox sparrows, which have the smallest distribution of the four. They spend the winter season in northeast California, before migrating to central Oregon in the summer to breed. They may not travel far, but they know what they like, and stick with it!<\/p>\n<\/div><\/div>\n\n\n

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(Image by David Sibley)<\/figcaption><\/figure>\n<\/div>\n\n\n

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Reproduction and Feeding Behaviour <\/p>\n\n\n\n

Fox sparrows are skilled foragers, typically spotted on the ground sorting through leaf litter, looking for their next meal. Their predation technique involves the \u201cdouble-scratch method<\/a>\u201d, where they scratch both feet backwards simultaneously after an initial forward hop. During breeding season, insects are the best food choice, acting as a protein source that supports the growth of their young. In the winter and during migration, their menu expands to include seeds, fruits, plant buds, or invertebrates.<\/p>\n\n\n\n

When it comes to raising a family, fox sparrows are just as resourceful. Their nests are surprisingly difficult to find in the breeding season. In western North America, they hide under dense trees while foraging.  In eastern North America, they breed under coniferous forests or on upturned stumps. Females establish their nests in  2-3 days<\/a>, assembling coarse forest debris, twigs, moss and lichens around an interior lining of fine insulating materials (like rootlets or fine grass). This carefully crafted nest provides a safe home for 2-5 eggs, which are nurtured until they hatch.  <\/p>\n\n\n\n

But raising chicks comes with some danger. Fox sparrow parents are highly alert during breeding season for predators such as merlins, steller’s jays, snakes, chipmunks and weasels (Cornell Lab of Ornithology, n.d.<\/a>). When threatened, parents teach their young to evade predation by using a metallic chip to pretend to have a broken wing. It is a dramatic reminder that beneath their quiet ground-foraging lifestyle is a surprisingly adaptive and protective parent,<\/p>\n\n\n\n

Singing Behaviour<\/p>\n\n\n\n

Fox sparrows enjoy their independence, but they are far from silent. These birds\u2019 recognizable trait is their beautiful variation of songs.  In particular, the males of the eastern population are known for their rich songs that vary between the subspecies.<\/p>\n\n\n\n

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(Song #1<\/a> “Red” subspecies)<\/p>\n\n\n\n

(Song #2<\/a> Slate-colored subspecies)<\/p>\n\n\n\n

(Song #3<\/a> Thick-billed subspecies)<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n\n\n\n

<\/p>\n\n\n\n

Their songs begin with one or more clear whistles before breaking into short trills or chirps. Western populations can have three to four song types, while northern and eastern species have two to three. Overall, calls vary depending on the population, but common sounds are described as sharp \u201csmack<\/a>\u201d or chu-chu calls.<\/p>\n\n\n\n

(Call #1<\/a> “Red” subspecies)<\/p>\n\n\n\n

(Call #2<\/a> Thick-billed subspecies)<\/p>\n<\/div><\/div>\n\n\n\n

These songs are more than just beautiful background music; they may reveal who these birds are. Researchers<\/a> found striking variations in the \u201cbuzzy\u201d syllables that fox sparrows use. For example, slate-colored fox sparrows had 97% of their songs containing the buzzy syllable, compared to 53% of thick-billed fox sparrows. The vocalizations collected and observed in this study allowed researchers to distinguish subspecies based on songs, which means that fox sparrows’ songs are like their own musical fingerprint.<\/p>\n\n\n\n

Another motivation for singing in fox sparrows is territory.  Researchers<\/a> on eastern fox sparrows observed males singing regularly within their traditional migration areas, where one male fox sparrow aggressively sang to a recording of another fox sparrow’s song. So, the next time you hear a fox sparrow singing, listen closely; it could be just telling you to leave.<\/p>\n\n\n\n

Conservation Status<\/p>\n\n\n\n

Fox sparrows are a highly adaptive species that have spread across North America. Anthropogenic impacts, such as logging and forest fires, have altered fox sparrow habitat selection, as they thrive in the shrubs that result. Additionally, fox sparrows commonly breed in remote regions in North America that are not currently disturbed by humans. According to the Continental Concern Score<\/a> assessment, there is a low conservation concern for this species, where it is rated 8 out of 20. <\/p>\n\n\n

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(Image by North American Bird Conservation Initiative<\/a>, 2016)<\/figcaption><\/figure>\n<\/div>\n\n\n

Recent Research<\/p>\n\n\n\n

Genetics:<\/p>\n\n\n\n

One fascinating aspect of fox sparrow species is their incredible variety of appearances. With so many distinct subspecies, you might wonder: are they all really related?  In short, yes, but their genetic history is more complicated than their plumage suggests. In 2025<\/a>, one study observed how different sparrow populations are genetically connected. The results showed that different sparrow species with overlapping ranges experienced interbreeding and hybridization. This study on wild sparrow crossbreeding was inclusive of fox sparrows, suggesting that fox sparrows and other sparrow species hybridize, which could result in plumage variation in their progeny.<\/p>\n\n\n\n

Competition:<\/p>\n\n\n\n

Fox sparrow foraging behaviours have been shown to impact other bird species that share a similar niche, such as the song sparrow. A 45-year study<\/a> on Mandarte Island, British Columbia, observed what happens when fox sparrows entered a habitat already occupied by song sparrows.  The new habitat colonized by fox sparrows created strong competition with native song sparrows. Fox sparrows dominated, causing song sparrows to relocate to other areas, which was observed in 91 – 100% of the interactions! Instances of niche competition were typically observed in the winter, when fox and song sparrows directly competed for seeds to forage. The arrival of fox sparrows to their winter feeding grounds was correlated with a 48% decrease in juvenile song sparrows’ survival. These findings reinforce the fact that fox sparrows are not only cute, but also formidable competition for their look-alikes.<\/p>\n\n\n\n

References <\/p>\n\n\n\n

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  1. Britannica Editors (2026, March 30). John Burroughs. Encyclopedia Britannica. https:\/\/www.britannica.com\/biography\/John-Burroughs<\/a> <\/li>\n<\/ol>\n\n\n\n
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    1. Burroughs, J. (2010). A spring relish. In C. Johnston (Illus.), A year in the fields<\/em> (pp. 37-52). Houghton, Mifflin and Company. Project Gutenberg. https:\/\/www.gutenberg.org\/files\/31292\/31292-h\/31292-h.htm#illus10<\/a>  (Original work published 1875)   <\/li>\n<\/ol>\n\n\n\n
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      1. Cornell Lab of Ornithology. 2025. All About Birds. Cornell Lab of Ornithology, Ithaca, New York. https:\/\/www.allaboutbirds.org<\/a> Accessed on October 8, 2026. <\/li>\n<\/ol>\n\n\n\n
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        1. Lipton, E. (2017). Fox sparrow<\/em> [Photograph]. Macaulay Library. https:\/\/macaulaylibrary.org\/asset\/48144671<\/a> <\/li>\n<\/ol>\n\n\n\n
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          1. Fox sparrows<\/em>. (n.d.). Alaska songbird institute. Retrieved September 28, 2026, from https:\/\/aksongbird.org\/bird-guide-fox-sparrow\/<\/a> <\/li>\n<\/ol>\n\n\n\n
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            1. Johnson KM, Germain RR, Tarwater CE, Reid JM, Arcese P. Demographic consequences of invasion by a native, controphic competitor to an insular bird population. Oecologia. 2018 May;187(1):155-165. https:\/\/doi.org\/10.1007\/s00442-018-4101-y.<\/a>Epub 2018 Mar 2. PMID: 29500488.  <\/li>\n<\/ol>\n\n\n\n
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              1. Kevin C. Fraser, Am\u00e9lie Roberto-Charron, Bruce Cousens, Michael Simmons, Ann Nightingale, Amanda C. Shave, Ren\u00e9e L. Cormier, Diana L. Humple, Classic pattern of leapfrog migration in Sooty Fox Sparrow (Passerella iliaca unalaschcensis<\/em>) is not supported by direct migration tracking of individual birds, The Auk<\/em>, Volume 135, Issue 3, 1 July 2018, Pages 572\u2013582, https:\/\/doi.org\/10.1642\/AUK-17-224.1<\/a> <\/li>\n<\/ol>\n\n\n\n
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                1. Lloyd JD. The recent expansion of Fox Sparrow (Passerella iliaca iliaca<\/em>) breeding range into the northeastern United States. PeerJ. 2018 Dec 10;6: e6087. https:\/\/doi.org\/10.7717\/peerj.6087.<\/a> PMID: 30581676; PMCID: PMC6292377.  <\/li>\n<\/ol>\n\n\n\n
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                  1. Lloyd, J. (2018, October 3). Fox sparrows: A boreal bird on the move<\/em>. Vermont Center for Ecostudies. https:\/\/vtecostudies.org\/blog\/fox-sparrows-a-boreal-bird-on-the-move\/<\/a> <\/li>\n<\/ol>\n\n\n\n
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                    1. National Audubon Society. (n.d.). Fox sparrow<\/em>. Audubon. Retrieved October 8, 2026, from https:\/\/www.audubon.org\/field-guide\/bird\/fox-sparrow<\/a>  <\/li>\n<\/ol>\n\n\n\n
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                      1. North American Bird Conservation Initiative. (2016). State of north america’s birds 2016: Species <\/em>    assessment summary and watch list<\/em> [Research report]. North American Bird Conservation Initiative (NABCI). https:\/\/www.stateofthebirds.org\/2016\/resources\/species-assessments\/<\/a>  <\/li>\n<\/ol>\n\n\n\n
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                        1. Pandolfino, Edward & Douglas, Lily & Pyle, Peter. (2023). VOCALIZATIONS AND BILL MEASUREMENTS MAY RESOLVE SOME QUESTIONS ABOUT TAXONOMIC RELATIONSHIPS WITHIN THE FOX SPARROW COMPLEX. Western Birds. 54. 117-132. https:\/\/doi.org\/10.21199\/WB54.2.2<\/a> . <\/li>\n<\/ol>\n\n\n\n
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                          1. Rottenborn, S. (2018). Fox sparrow<\/em> [Photograph]. Macaulay Library. https:\/\/macaulaylibrary.org\/asset\/124922961<\/a> <\/li>\n<\/ol>\n\n\n\n
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                            1. Sibley, D. A. (2016). Emberizine sparrows and their allies. In D. A. Sibley (Author), The sibley<\/em> field guide to birds of western north america<\/em> (Second ed., p. 408). Alfred A. Knopf. <\/li>\n<\/ol>\n\n\n\n
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                              1. tinyfishy. (2008). Fox sparrow<\/em> [Photograph]. Flickr. https:\/\/www.flickr.com\/photos\/tinyfishy\/2777046996\/in\/photostream\/<\/a> <\/li>\n<\/ol>\n\n\n\n
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                                1. Weckstein, J. D., D. E. Kroodsma, and R. C. Faucett (2020).\u202fFox Sparrow\u202f(Passerella iliaca<\/em>), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.\u202fhttps:\/\/doi.org\/10.2173\/bow.foxspa.01<\/a> <\/li>\n<\/ol>\n\n\n\n
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                                  1. Wiens, B.J., DeCicco, L.H. & Colella, J.P. triangulaR:<\/em> an R package for identifying AIMs and building triangle plots using SNP data from hybrid zones. Heredity<\/em> 134<\/strong>, 251\u2013262 (2025). https:\/\/doi.org\/10.1038\/s41437-025-00760-2<\/a>  <\/li>\n<\/ol>\n\n\n\n

                                    <\/p>\n","protected":false},"excerpt":{"rendered":"

                                    Photo by John Lloyd<\/p>\n","protected":false},"author":6324,"featured_media":7879,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-7787","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/posts\/7787","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/users\/6324"}],"replies":[{"embeddable":true,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/comments?post=7787"}],"version-history":[{"count":8,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/posts\/7787\/revisions"}],"predecessor-version":[{"id":7911,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/posts\/7787\/revisions\/7911"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/media\/7879"}],"wp:attachment":[{"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/media?parent=7787"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/categories?post=7787"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wordpress.viu.ca\/biol325\/wp-json\/wp\/v2\/tags?post=7787"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}