Animal Diversity Web

Di­ver­sity

Uro­cyon, de­rived from the Greek word for “tailed dog”, is a genus of Canidae, the fam­ily that is com­posed of coy­otes, dogs, foxes, jack­als, and wolves. The sci­en­tific name of Uro­cyon can be at­trib­uted to the au­thor Baird in 1857. Also known as gray foxes (not to be con­fused with the species), this genus en­com­passes two species: the gray fox Uro­cyon cinereoar­gen­teus, and the smaller gray fox species, is­land fox Uro­cyon lit­toralis. These two species to­gether rep­re­sent the most basal clade within the ex­tant Canidae.

Div­ing into the nat­ural his­tory of this taxon, the lin­eage lead­ing to Uro­cyon ini­tially di­verged from other canids dur­ing the Miocene, which was 8-12 mil­lion years (MY) ago. Re­search has found that fos­sil Uro­cyon, or gray foxes that have gone ex­tinct, has been pre­sent in North Amer­ica since the early Pliocene (~5 MY). Con­tem­po­rary Uro­cyon, or gray foxes that are cur­rently ex­tant, is the only ex­tant canid with a nat­ural range span­ning both North and South Amer­ica. Con­tem­po­rary gray foxes have been clas­si­fied into 15 sub­species based on mor­phol­ogy, in ad­di­tion to six sub­species of is­land fox.

Cur­rently, U. cinereoar­gen­teus is listed as a “Least Con­cern” species in IUCN, while U. lit­toralis is listed as “Near Threat­ened” mainly due to in­fec­tious dis­eases. Con­ser­va­tion ef­forts and fur­ther re­search have been con­ducted, as well as con­struct­ing meth­ods to mit­i­gate dis­ease in is­land foxes. (Coo­nan, et al., 2013; God­dard, et al., 2015; "Gray Foxes (Genus Uro­cyon)", 2021; Sanchez and Hud­gens, 2020; Wil­son and Reeder, 2007)

Ge­o­graphic Range

Uro­cyon can be found from south­ern Canada to south­ern United States as a na­tive in the Nearc­tic re­gion, along with its na­tive range also ex­tend­ing through north­ern Colom­bia and Venezuela in the Neotrop­i­cal re­gion. It is, how­ever, not found in some moun­tain­ous parts of the North­west United States and in the Great Plains. More specif­i­cally for is­land foxes, as their name im­plies, the range of U. lit­toralis con­sists of the six Chan­nel Is­lands off the coast of south­ern Cal­i­for­nia. In the North­ern Chan­nel Is­land com­plex, they are found on San Miguel, Santa Rosa, and Santa Cruz Is­lands. In the South­ern Chan­nel Is­lands, they occur on San Nico­las, Santa Catalina, and San Clemente Is­lands.

An­nual home range sizes of Uro­cyon are vari­able across their ge­o­graph­i­cal range, rang­ing from 75 ha to 676 ha, with most stud­ies re­port­ing es­ti­mates rang­ing from 100 ha to 350 ha. (Deuel, et al., 2017a; God­dard, et al., 2015; "Gray Foxes (Genus Uro­cyon)", 2021; Hof­man, et al., 2015; Liu, 2002; Vu, 2011)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native

• Other Geographic Terms
• island endemic

Habi­tat

Uro­cyon is con­sid­ered as habi­tat gen­er­al­ists, but has a pref­er­ence for se­lect­ing habi­tats con­tain­ing for­est cover, such as hard­wood forests, mixed pine-hard­wood forests, ma­ture pine forests, mid-ro­ta­tion pine plan­ta­tions, and even res­i­den­tial areas and agri­cul­ture close to human dwellings. Of all canids, gray foxes are thought to be the most closely as­so­ci­ated with hard­wood forests, and many stud­ies have also doc­u­mented the com­mon pref­er­ence of mixed pine/hard­wood forests by gray foxes. Stud­ies have found that gray foxes are tol­er­ant of urban and sub­ur­ban land­scapes, but use of sub­ur­ban land­scapes may also be lim­ited by fac­tors such as in­ter­ac­tions with larger car­ni­vores. For is­land foxes on the Chan­nel Is­lands, they can also be found in val­ley and foothill grass­lands, is­land chap­ar­ral, and coastal marshes.

Uro­cyon habi­tat se­lec­tion also varies sea­son­ally with avail­abil­ity of re­sources, e.g. soft mast, small mam­mals, birds, and in­sects. Dur­ing the day, gray foxes are more often found in habi­tat types with dense brushy un­der­sto­ries, whereas at night, stud­ies have found that habi­tat se­lec­tion does not occur. Gray foxes have been ob­served in dens lo­cated in un­der­ground bur­rows and hol­low trees or logs. (Cooper, et al., 2012; Deuel, et al., 2017b; Deuel, et al., 2017a; Egan, et al., 2021; Kapfer and Kirk, 2012; Liu, 2002; Moore and Collins, 1995; Tem­ple, et al., 2010; Vu, 2011)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• savanna or grassland
• chaparral
• forest

• Other Habitat Features
• urban
• suburban
• agricultural

Sys­tem­atic and Tax­o­nomic His­tory

Dur­ing the Miocene, which oc­curred 8-12 MY ago, the lin­eage lead­ing to Uro­cyon ini­tially di­verged from other canids. The genus has been pre­sent in North Amer­ica since the Hemphillian land mam­mal age (Pliocene; ~5 MY). Con­tem­po­rary Uro­cyon re­mains as the only ex­tant canid with a nat­ural range through North and South Amer­ica. Fos­sil records show that U. cinereoar­gen­teus has been found at al­most 40 Pleis­tocene lo­cal­i­ties, the old­est of which date back to the late Irv­ing­ton­ian or pos­si­bly the early Irv­ing­ton­ian. These records also have found that U. lit­toralis ev­i­dently reached the Chan­nel Is­lands off Cal­i­for­nia in the late Pleis­tocene. The genus Uro­cyon is con­sid­ered to be the most basal of the liv­ing canids.

The nam­ing of the genus Uro­cyon can be at­trib­uted to the au­thor Baird in 1857. This genus has no names that it was pre­vi­ously known as. How­ever, the gray fox species U. lit­toralis was orig­i­nally named Vulpes lit­toralis in 1857, with other com­mon names for the is­land fox that in­clude coast fox, short-tailed fox, is­land gray fox, chan­nel is­land fox, chan­nel is­lands gray fox, Cal­i­for­nia chan­nel is­land fox, and in­su­lar gray fox.

Two re­cent re­vi­sions of the fam­ily Canidae have sug­gested that Uro­cyon should be in­cluded as a sub­genus of Vulpes by Clut­ton-Brock et al. in 1976. How­ever, ge­netic analy­ses of the fox-like canids con­firmed that Uro­cyon is a dis­tinct genus from the red foxes (Vulpes). Ge­net­i­cally, Uro­cyon often clus­ters with two other an­cient lin­eages: the east Asian rac­coon dog (Nyc­tereutes pro­cy­onoides) and the African bat-eared fox (Oto­cyon mega­lo­tis). Re­cent mi­to­chon­dr­ial ge­netic stud­ies sug­gest di­ver­gence of North Amer­i­can east­ern and west­ern gray foxes in the Irv­ing­ton­ian, mid-Pleis­tocene into sep­a­rate sis­ter taxa.

Gray foxes share many di­ag­nos­tic char­ac­ter­is­tics with other North Amer­i­can foxes, such as red foxes (Vulpes vulpes) and fen­necs (Vulpes zerda). How­ever, gray foxes have dif­fer­ent char­ac­ter­is­tics and be­hav­iors com­pared to some of their fox rel­a­tives that can eas­ily dis­tin­guish them from the oth­ers. (Fritzell and Harold­son, 1982; Gef­fen, et al., 1992; God­dard, et al., 2015; Liu, 2002; Wil­son and Reeder, 2007)

• Synapomorphies

  • Guard hairs
  • Vibrissae
  • Pointed ears
  • Digitigrade
  • Bushy tail
  • Semi-retractable claws

Phys­i­cal De­scrip­tion

Uro­cyon is char­ac­ter­ized with a griz­zled ap­pear­ance on the back and sides due to in­di­vid­ual guard hairs that are banded with white, gray, and black. Typ­i­cally, gray foxes have a total body length of 800 to 1125 mm, with a tail that is be­tween 275 to 443 mm long. They also typ­i­cally have a hind­foot length be­tween 100 to 150 mm. Adult weights range from about 3 to 7 kg. It is to note that U. lit­toralis is a dwarf ver­sion of U. cinereoar­gen­teus, with adults weigh­ing be­tween 1 to 3 kg, along with smaller body lengths be­tween 590 to 790 mm. In both Uro­cyon species, males tend to be slightly larger than fe­males, but in­di­vid­u­als of both sexes fall into the same length and weight ranges.

Uro­cyon have dis­tinc­tive black, white, and red­dish-brown fa­cial mark­ings, with a buff and gray col­ored un­der­fur. White fur shows on the ears, throat, chest, belly, and hind legs. Parts of the neck, sides, and limbs are de­scribed to be “cin­na­mon-ru­fous” col­ored (yel­low or or­ange col­oration). There is also a pre­dom­i­nance of black-tipped hairs near the mid­dle of the back that forms a dark, lon­gi­tu­di­nal stripe. The stripe ex­tends into a con­spic­u­ous black mane of coarse hair on the top of a black-tipped tail. Gray foxes have pointed ears, a pointed muz­zle, and long hooked claws that are semi-re­tractable. Com­pared to adult gray foxes, new­born pups typ­i­cally have dark brown col­oration, along with a thicker dor­sal fur coat. (Fritzell and Harold­son, 1982; Gomp­per, et al., 2006; Liu, 2002; Moore and Collins, 1995; Vu, 2011)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger

Re­pro­duc­tion

Both ex­tant species of Uro­cyon are con­sid­ered as pri­mar­ily monog­a­mous. Adult gray foxes are so­cially monog­a­mous and form pair-bonds, which con­tribute to the spa­tial be­hav­ior of each pair mem­ber. Pair for­ma­tion and courtship gen­er­ally occur from Jan­u­ary through March, with most breed­ing oc­cur­ring in late Feb­ru­ary and early March. Dur­ing mat­ing sea­son, com­pe­ti­tion in­creases due to the need to at­tract mates, es­pe­cially for males that dis­play more ag­gres­sion while de­fend­ing mates. For ex­am­ple, they will some­times give off a se­ries of sharp barks or yips to at­tract their mate. An­other method that gray foxes use to at­tract mates is the pres­ence of scent glands on their face, pads of their feet, and in­side their anus. These glands are pri­mar­ily used to de­mar­cate ter­ri­tory, but they are also used to at­tract po­ten­tial mates.

One study has re­ported on a sin­gle mated pair that was found to­gether 13.5% of the time. An­other study ra­dio-tracked two mated pairs dur­ing parts of the breed­ing and den­ning sea­sons. They found that the males for­aged sep­a­rately from the fe­males at night, and usu­ally re­turned to the den at day­light. Com­pared to the fe­males, the males did not make re­peated trips to the den. When the young reached 3 months of age, they ac­com­pa­nied their moth­ers as they left the den, and by 4 months of age, they started to for­age in­de­pen­dently.

It was also ob­served in an­other study where mated gray foxes were closer than ex­pected to each other within their home ranges. In­ter­ac­tions among mem­bers of a mated pair may dif­fer at fine tem­po­ral scales. Be­cause gray foxes are so­cially monog­a­mous, spa­tial over­lap is com­mon be­tween adults in a pair-bond and these pairs main­tain ex­clu­sive ter­ri­to­ries. Re­searchers sug­gest that the over­lap among non-paired in­di­vid­u­als is likely due to the re­sult of re­lat­ed­ness among over­lap­ping in­di­vid­u­als. In­di­rect ob­ser­va­tions of so­cial or­ga­ni­za­tion of gray foxes sug­gest that fam­ily units, com­posed of an adult male, adult fe­male, and pos­si­bly ju­ve­niles, main­tain spa­tially or tem­po­rally sep­a­rate home ranges. The mated pair will re­main to­gether until late fall, but then will gen­er­ally be soli­tary dur­ing the win­ter. (Deuel, et al., 2017b; Fritzell and Harold­son, 1982; Moore and Collins, 1995; Schutz, et al., 2009; Vu, 2011)

• Mating System
• monogamous

The breed­ing sea­son of Uro­cyon varies ge­o­graph­i­cally, though gen­er­ally breed­ing ac­tiv­ity ex­tends from late Jan­u­ary to May. The num­ber of off­spring per breed­ing sea­son is an av­er­age be­tween three to four young per fe­male, though for U. lit­toralis specif­i­cally, lit­ter size can also range from one to five, with usu­ally an av­er­age of two or three.

The ges­ta­tion pe­riod of gray foxes is un­known; how­ever, it has been re­ported to be an av­er­age of 63 days for U. cinereoar­gen­teus, and a range be­tween 50 to 53 days for U. lit­toralis. Par­tu­ri­tion usu­ally oc­curs from the end of April through early May. There have been no di­rect ob­ser­va­tions of par­tu­ri­tion for U. lit­toralis, but stud­ies sug­gest that the young of is­land foxes are born blind and help­less. Pups are typ­i­cally weaned for over three to four weeks, though wean­ing is usu­ally com­plete at about 6 weeks. The par­ents (pri­mar­ily the fe­male) start bring­ing solid food to the young be­fore they are com­pletely weaned.

Stud­ies have found that the young emerge from the den at about three to four weeks of age. When pups reach two months of age, they spend most of the day out­side of the den, and then they begin to for­age with their par­ents in mid- to late June, and will con­tinue to re­main with their par­ents through­out the sum­mer. The par­ents dis­perse away from the natal home range in late Sep­tem­ber, but the pups will re­main in their natal areas until at least De­cem­ber. Both males and fe­males are sex­u­ally ma­ture by 10 months of age, soon after dis­per­sal. It has been re­ported that ju­ve­nile gray foxes have dis­persed as far as 84 km from their natal area. (El­broch and Allen, 2013; Fritzell and Harold­son, 1982; Moore and Collins, 1995; Vu, 2011)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

Both male and fe­male par­ents take care of the off­spring in the two ex­tant species of Uro­cyon. Dur­ing pre-fer­til­iza­tion in a mated pair, the male will pri­or­i­tize hunt­ing for re­sources, while the fe­male will pri­or­i­tize search­ing for a den. After birth, both the mother and fa­ther will pro­tect their pups. Dur­ing the pre-in­de­pen­dence pe­riod, the fa­ther is typ­i­cally pro­vid­ing most of the food scraps, as well as teach­ing pups hunt­ing skills. At three to six weeks, the pups are weaned and ready to hunt on their own. Both par­ents hunt for food sep­a­rately at this point, since the pups are learn­ing to hunt in­de­pen­dently. Pups leave their mother in the fall when they are about 10 months old, since they’re sex­u­ally ma­ture and ready to dis­perse at that stage.

Al­though gray foxes lack sig­nif­i­cant sex­ual di­mor­phism, home range sizes of males are gen­er­ally slightly larger than fe­males. How­ever, male and fe­male home ranges are both smaller and move­ment rates are less dur­ing den­ning, sug­gest­ing some de­gree of male in­vest­ment in rear­ing young. Home ranges tend to be largest dur­ing breed­ing sea­son, when pup rear­ing re­spon­si­bil­i­ties have di­min­ished and re­source abun­dance may be low. Ad­di­tion­ally, home ranges are in­ter­me­di­ate dur­ing pup-rear­ing sea­son, and the small­est while den­ning when adult move­ments are re­stricted as a re­sult for car­ing for young.

Stud­ies have found that adult gray foxes have rel­a­tively low an­nual sur­vival rates, and both sexes con­tinue to in­de­pen­dently rear pups fol­low­ing mate loss, with a lone male’s abil­ity to rear pups being de­pen­dent on whether pups have been weaned. When the pups dis­perse from their natal range, lone adults may be mo­ti­vated to seek out a new mate to pair with for the up­com­ing breed­ing sea­son if their mate died be­tween the time of whelp­ing and pup dis­per­sal. (Deuel, et al., 2017a; Fritzell and Harold­son, 1982; Moore and Collins, 1995; Vu, 2011)

• Parental Investment
• precocial
• male parental care
• female parental care
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • male
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifes­pan/Longevity

Uro­cyon has a typ­i­cal lifes­pan (cap­tive and wild) that ranges be­tween 6 to 8 years. There has been a re­port of gray foxes liv­ing up to 10 years in the wild, and 12 years in cap­tiv­ity. How­ever, due to U. lit­toralis being the largest en­demic post-Pleis­tocene land mam­mal on the Chan­nel Is­lands, is­land foxes have been fac­ing a de­creased lifes­pan in the wild. There is cur­rently no de­fin­i­tive av­er­age of their lifes­pan. (Fritzell and Harold­son, 1982; Hof­man, et al., 2015; Vu, 2011)

Be­hav­ior

Uro­cyon mainly live a soli­tary, motile lifestyle. For U. cinereoar­gen­teus, this species of gray fox is pri­mar­ily noc­tur­nal and cre­pus­cu­lar, with stud­ies re­port­ing that they travel greater dis­tances per hour at night than dur­ing the day. How­ever, local shifts in di­ur­nal rest­ing places are com­mon as well. Usu­ally, this species hunts at night and spends the day sleep­ing in hol­low logs or un­der­ground bur­rows.

Com­pared to U. cinereoar­gen­teus, U. lit­toralis has been ob­served to have more day­time ac­tiv­ity, with peaks oc­cur­ring dur­ing pe­ri­ods of low light in­ten­sity (e.g. sun­set and sun­rise). Ra­dioteleme­try stud­ies have re­ported that the ac­tiv­ity pat­terns of is­land foxes vary sea­son­ally in re­sponse to changes in am­bi­ent air tem­per­a­ture. For ex­am­ple, dur­ing the sum­mer, is­land foxes show very lit­tle ac­tiv­ity dur­ing the mid­dle of the day, but they are most ac­tive dur­ing early morn­ings and evenings. On the other hand, dur­ing the win­ter, lit­tle ac­tiv­ity oc­curs dur­ing early morn­ings and evenings, while most of the for­ag­ing oc­curs dur­ing the day.

A no­table lo­co­mo­tion that gray foxes are known for are their agile, tree-climb­ing be­hav­ior (scan­so­r­ial lo­co­mo­tion). Stud­ies have ob­served gray foxes climb­ing ver­ti­cal, branch­less tree trunks with their semi-re­tractable claws. They are able to grasp the trunk with their fore­limbs and then push up the trunk with their hindlimbs. Gray foxes have also been ob­served jump­ing from branch to branch, and de­scend­ing down the trunk by ei­ther back­ing down the ver­ti­cal tree or run­ning head­first down a slop­ing tree. Some of the rea­sons why they climb trees are be­cause of for­ag­ing pur­poses, rest­ing, or es­cap­ing from preda­tors.

Based on ra­dioteleme­try stud­ies and rel­a­tive trap suc­cess, the so­cial or­ga­ni­za­tion of gray foxes have been ob­served to con­sist of fam­ily units, com­pris­ing an adult male and fe­male, and pos­si­bly ju­ve­niles, in which they main­tain spa­tially or tem­po­rally sep­a­rate home ranges. How­ever, one study ob­served a home range of four gray foxes, con­sist­ing of two males and two fe­males, that oc­cu­pied the same area dur­ing the spring and sum­mer. (Fritzell and Harold­son, 1982; Liu, 2002; Moore and Collins, 1995; Vu, 2011)

• Key Behaviors
• scansorial
• terricolous
• diurnal
• nocturnal
• crepuscular
• motile
• nomadic
• daily torpor
• solitary
• territorial
• social

Com­mu­ni­ca­tion and Per­cep­tion

Uro­cyon com­mu­ni­cates with one an­other using vi­sual, tac­tile, acoustic, and chem­i­cal sig­nals. This in­cludes the typ­i­cal bark­ing and growl­ing com­mu­ni­ca­tion be­hav­ior. They are com­monly heard bark­ing at night. A study has re­ported the prin­ci­pal sound fre­quen­cies of the bark of gray foxes. For ex­am­ple, U. lit­toralis barks have been com­pared to the barks of a rat ter­rier. Gray foxes also gen­er­ally pro­duce hisses and short, sharp growls dur­ing in­traspe­cific ag­gres­sion. All types of vo­cal­iza­tions are used by both sexes to es­tab­lish dom­i­nance be­tween in­di­vid­u­als dur­ing in­traspe­cific en­coun­ters.

An ob­ser­va­tion of a so­cial com­mu­ni­ca­tion in­volves young gray foxes (5 to 8 weeks old) fre­quently rais­ing a hind leg to show their gen­i­talia to a con­spe­cific, rep­re­sent­ing a sub­mis­sive or ap­pease­ment ges­ture. An­other study as­sessed that this leg-lift­ing be­hav­ior in ju­ve­niles seemed to be a mu­tual greet­ing, as paired pups were ob­served in mu­tual leg-lift­ing and smelling of each other’s gen­i­talia after ap­proach­ing one an­other. A third study ob­served a more ag­gres­sive-dom­i­nant be­hav­ior of the largest pup in the den pre­sent­ing their gen­i­talia to a runt, in which the dom­i­nant pup at­tacked the runt after the runt at­tempted to avoid it.

Ju­ve­niles also com­monly play fight, where ag­gres­sive or play­ful at­tacks be­tween gray foxes are di­rected at the cheek. Since the cheek is where the skin is es­pe­cially thick, no crit­i­cal dam­age is done dur­ing play fights. In­traspe­cific fight­ing is often ac­com­pa­nied by growl­ing, bark­ing, tail and ear bit­ing, chas­ing, scuf­fling, and hip slam­ming.

Ad­di­tion­ally, ol­fac­tory cues from urine and feces de­po­si­tion play a role in in­traspe­cific gray fox com­mu­ni­ca­tion, along with how gray foxes per­ceive their en­vi­ron­ment. Ev­i­dence of this has been found in both ex­tant species, where the de­po­si­tion of urine and feces have been iden­ti­fied in con­spic­u­ous lo­ca­tions, such as on logs, rocks, small bushes, sticks, bare ground, and other el­e­vated sites, as well as along trails and road edges. These scats are often de­posited in groups. For adult gray foxes, mark­ing of ter­ri­to­ries and food are done by using their scent glands. Fur­ther­more, vi­sual and acoustic cues are preva­lent dur­ing for­ag­ing pe­ri­ods, es­pe­cially hunt­ing at night, as this al­lows gray foxes to be more alert for prey and be more suc­cess­ful with food cap­tures. (El­broch and Allen, 2013; Fritzell and Harold­son, 1982; Moore and Collins, 1995; Vu, 2011)

• Communication Channels
• tactile
• acoustic
• chemical

• Other Communication Modes
• pheromones
• scent marks

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Uro­cyon has an om­niv­o­rous diet, which con­sists of a va­ri­ety of food de­pend­ing on cer­tain lo­ca­tions, sea­sons, and re­source avail­abil­ity. This va­ri­ety can in­clude small ver­te­brates, fruit, seeds, and in­ver­te­brates. Both ex­tant gray fox species U. cinereoar­gen­teus and U. lit­toralis have slightly dif­fer­ent diets based on their re­source avail­abil­ity due to their var­ied habi­tats.

In mul­ti­ple east­ern and cen­tral states of the U.S., mam­mals are the pre­dom­i­nant prey for U. cinereoar­gen­teus, then fol­lowed by fruit and seeds, in­ver­te­brates, an­thro­pogenic items, and birds. Dur­ing the win­ter, lago­morphs (e.g. cot­ton­tail rab­bits (Sylvi­la­gus)), ro­dents (e.g. voles Mi­cro­tus, deer mice Per­omyscus, woodrats Neotoma, and cot­ton rats Sig­modon)) com­pose the largest por­tion of U. cinereoar­gen­teus. Dur­ing sum­mer and au­tumn sea­sons, in­ver­te­brates (pre­dom­i­nantly or­thopter­ans, an order of in­sects which con­sists of grasshop­pers, lo­custs, and crick­ets) mainly make up their diet. Ad­di­tion­ally, plant foods like per­sim­mon, berries, grapes, ap­ples, and corn also in­crease in im­por­tance dur­ing the au­tumn, pos­si­bly form­ing up to 70% of the diet by vol­ume. In one study, it was found that while an­a­lyz­ing gray fox scat com­pared to the coy­ote and bob­cat scat, fruit con­sump­tion was at a high fre­quency dur­ing the sum­mer and au­tumn, and al­most all fruits eaten were man­zanita berries. It was also found that when gray fox scats were largely com­posed of man­zanita berries, their di­etary breadth was nar­rower com­pared to coy­otes and bob­cats.

Less com­monly eaten foods by U. cinereoar­gen­teus are birds (in­clud­ing poul­try), squir­rels (Sci­u­rus), opos­sum (Didel­phis vir­gini­ana), and deer (Odocoileus) car­rion. How­ever, one study found that gray foxes were the prin­ci­pal preda­tors of red-faced war­bler (Cardel­lina rubrifrons) and yel­low-eyed junco (Junco phaeono­tus) nests within their study sys­tem, ac­count­ing for 89% of all nest depre­da­tions. Fur­ther­more, an­other study ob­served gray foxes in the Chi­huahuan Desert of north­ern Mex­ico and south­west­ern U.S. only scav­enged on fresh, 1- or 2-day-old car­rion.

The diet of U. lit­toralis is sim­i­lar when com­pared to U. cinereoar­gen­teus, but they pri­mar­ily eat a wide va­ri­ety of plants and an­i­mal re­mains. Is­land foxes are op­por­tunis­tic for­agers, in which they for­age on any food items en­coun­tered within their home range, and they gen­er­ally do not move great dis­tances to feed on abun­dant, yet lo­cal­ized food re­sources. Vary­ing ac­cord­ing to sea­sonal avail­abil­ity of foods and the par­tic­u­lar is­land sam­pled, is­land fox diet in­cludes mice, ground nest­ing birds, arthro­pods, and fruits. The im­por­tance of fruit in the diet of is­land foxes is re­lated to a plant's fruit­ing sea­son. Is­land foxes have lim­ited ver­te­brate prey due to the ver­te­brate fauna of the Chan­nel Is­lands being de­pau­per­ate. Com­pared to the gray fox, is­land foxes show a re­duced de­pen­dence on ver­te­brate prey. Mam­mals, es­pe­cially deer mice (Per­omyscus man­ic­u­la­tus), com­prise the largest ver­te­brate por­tion of the diets of is­land foxes on Santa Cruz Is­land, with deer mice com­pris­ing 53% of the vol­ume of win­ter feces. Other po­ten­tial ro­dent prey in­cludes Cal­i­for­nia ground squir­rels (Sper­mophilus beecheyi), west­ern har­vest mice (Re­i­throdon­to­mys mega­lo­tis), Cal­i­for­nia voles (Mi­cro­tus cal­i­for­ni­cus), black rats (Rat­tus rat­tus), and house mice (Mus mus­cu­lus). Rep­tiles and am­phib­ians have re­port­edly not con­sti­tuted a sig­nif­i­cant pro­por­tion of the over­all diet of is­land foxes, though the Pa­cific cho­rus frog (Pseudacris regilla) is the only am­phib­ian that is­land foxes are known to eat, and it has been sug­gested that is­land foxes may eat all species of rep­tiles that are found on the is­lands.

Human refuse areas and car­rion (e.g. car­casses of pigs, sheep, cat­tle, and ma­rine mam­mals), pro­vide sup­ple­men­tal food sources for is­land foxes, es­pe­cially when al­ter­nate foods are scarce. Like U. cinereoar­gen­teus, in­sects (par­tic­u­larly or­thopter­ans) are an im­por­tant food source for is­land foxes. For ex­am­ple, the Jerusalem cricket (g.​Stenopel­ma­tus sp.) is the most im­por­tant in­sect prey of is­land foxes. Dur­ing sum­mer and au­tumn sea­sons, grasshop­pers have been pre­dom­i­nantly found in the diets of is­land foxes. (El­broch and Allen, 2013; Fritzell and Harold­son, 1982; Kirk­patrick and Con­way, 2010; Lar­son, et al., 2015; Liu, 2002; Moore and Collins, 1995; Neale and Sacks, 2001; Vu, 2011)

• Primary Diet
• carnivore
  • eats terrestrial vertebrates
  • insectivore
  • eats non-insect arthropods
  • molluscivore
  • scavenger
• herbivore
  • frugivore
  • granivore
• omnivore

• Foraging Behavior
• stores or caches food

Pre­da­tion

The pri­mary preda­tors of Uro­cyon are golden ea­gles (Aquila chrysae­tos), bob­cats (Lynx rufus), coy­otes (Canis la­trans), and great horned owls (Bubo vir­gini­anus). Ad­di­tional preda­tors that more specif­i­cally prey on ju­ve­nile is­land foxes are red-tailed hawks (Buteo ja­maicen­sis), do­mes­tic dogs (Canis do­mes­ti­cus), com­mon ravens (Corvus corax) and bald ea­gles (Hali­aee­tus leu­co­cephalus). How­ever, hu­mans are con­sid­ered as the most sig­nif­i­cant preda­tor of adult gray foxes due to being hunted for fur or killed by farm­ers that con­sider them as pests. For ex­am­ple, it has been re­ported that the total fur har­vest of U. cinereoar­gen­teus in the U.S. in­creased from about 26,000 in­di­vid­u­als in 1970 to over 100,000 in­di­vid­u­als in 1975, with a five-fold in­crease in av­er­age pelt price over the same pe­riod.

An im­por­tant anti-preda­tor adap­ta­tion found in Uro­cyon is the re­tractable claws. These allow gray foxes to es­cape from ter­res­trial preda­tors by climb­ing up trees in an ef­fi­cient and agile man­ner. Gray foxes can also es­cape by hid­ing under brushes and uti­lize their cryp­tic col­oration, as their gray, black, white, and or­ange col­ors help them cam­ou­flage within the earthy tones of their sur­round­ings. (Fritzell and Harold­son, 1982; Liu, 2002; Moore and Collins, 1995; Vu, 2011)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • Bald eagle (Haliaeetus leucocephalus)
  • Bobcat (Lynx rufus)
  • Common raven (Corvus corax)
  • Coyote (Canis latrans)
  • Domestic dogs (Canis domesticus)
  • Golden eagle (Aquila chrysaetos)
  • Great horned owl (Bubo virginianus)
  • Red-tailed hawks (Buteo jamaicensis)

Ecosys­tem Roles

Uro­cyon plays an im­por­tant role in the ecosys­tem, es­pe­cially in terms of bal­anc­ing and main­tain­ing preda­tor-prey pop­u­la­tions and re­la­tion­ships. For ex­am­ple, due to being a gen­er­al­ist, the feed­ing habits of gray foxes leads to the reg­u­la­tion of small ro­dent pop­u­la­tions, as well as pre­vent­ing over­growth of veg­e­ta­tion in their en­vi­ron­ment. Not only are gray foxes im­por­tant preda­tors in ecosys­tems, they are also con­sid­ered as food sources to larger an­i­mals like golden ea­gles (Aquila chrysae­tos), bob­cats (Lynx rufus), coy­otes (Canis la­trans).

Ad­di­tion­ally, U. cinereoar­gen­teus has been found as a host to many par­a­sitic arthro­pods, such as fleas (Siphonaptera), lice (Ph­thi­raptera), ticks (Ixo­dida), chig­gers (Trom­bi­di­formes), and mites (Acari). A study found that un­like red foxes (Vulpes vulpes), gray foxes are highly re­sis­tant to in­fes­ta­tion by sar­cop­tic mange mites (Sar­coptes sca­biei). Gray foxes also host many species of in­ter­nal par­a­sites, such as trema­todes (Trema­toda), ces­todes (Ces­toda), ne­ma­todes (Ne­ma­toda), and acan­tho­cepha­lans (Acan­tho­cephala).

U. lit­toralis eat a wide va­ri­ety of plant and an­i­mal re­mains, so they are con­sid­ered as a key­stone species within their habi­tat. With­out is­land foxes, the nat­ural ecosys­tem of the is­lands will most likely col­lapse. By prey­ing on other is­land species, is­land foxes help keep their pop­u­la­tions down. (Fritzell and Harold­son, 1982; Moore and Collins, 1995; Vu, 2011)

• Ecosystem Impact
• keystone species

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

An eco­nomic im­por­tance for hu­mans is that Uro­cyon helps con­trol agri­cul­tural pest pop­u­la­tions, such as ro­dents (Ro­den­tia) and rab­bits (Lep­ori­dae).

The fur pelts of Uro­cyon are col­lected and sold by hu­mans via hunt­ing and trap­ping, though com­pared to the pelts of red foxes (Vulpes vulpes), gray foxes have shorter and coarser fur, thus mak­ing them less de­sir­able in the mar­ket. More specif­i­cally for U. lit­toralis, Na­tive Amer­i­cans have used their fur for arrow quiv­ers, capes, blan­kets, and head-dresses for cer­e­mo­nial prac­tices. In ad­di­tion to being oc­ca­sional hunt­ing tar­gets, gray foxes have been re­port­edly used for il­le­gal pet trade pur­poses. (Fritzell and Harold­son, 1982; Hof­man, et al., 2015; Liu, 2002; Moore and Collins, 1995; Vu, 2011)

• Positive Impacts
• pet trade
• body parts are source of valuable material
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Like most wild mam­mals, gray foxes carry a range of dis­eases. Uro­cyon is ca­pa­ble of being a car­rier of zoonotic dis­eases that pose a threat to hu­mans, such as ra­bies and lep­tospiro­sis. An­other oc­ca­sional prob­lem that gray foxes cause for hu­mans is the threat to poul­try farm­ers. (Fritzell and Harold­son, 1982; Moore and Collins, 1995; Vu, 2011)

• Negative Impacts
• injures humans
  • causes disease in humans
  • carries human disease
• causes or carries domestic animal disease

Con­ser­va­tion Sta­tus

In the genus Uro­cyon, U. cinereoar­gen­teus cur­rently has a sta­ble pop­u­la­tion and listed as “Least Con­cern” in IUCN, while U. lit­toralis is cur­rently listed as “Near Threat­ened” in IUCN, though there seems to be a slight in­crease trend in pop­u­la­tion size.

Al­though the pop­u­la­tion size of the gray fox is sta­ble, local pop­u­la­tions are fac­ing the threat of dis­eases, in­clud­ing ra­bies, ca­nine dis­tem­per, tu­laremia, lis­te­rio­sis, lep­tospiro­sis, histo­plas­mo­sis, tox­o­plas­mo­sis, and Tyzzer’s dis­ease. An­other fac­tor to con­sider is the hunt­ing and trap­ping of gray foxes by hu­mans dur­ing the reg­u­lated sea­son. How­ever, no spe­cial con­ser­va­tion ef­forts have been made to ad­dress this issue due to the large abun­dance of gray foxes cur­rently.

The is­land fox is the largest en­demic post-Pleis­tocene land mam­mal on the Chan­nel Is­lands. Dis­ease trans­mis­sion and epi­demic pre­ven­tion have top pri­or­ity in con­ser­va­tion ef­forts, es­pe­cially for small, iso­lated pop­u­la­tions like the is­land fox, which has a his­tory of sub­stan­tial pop­u­la­tion de­cline due to in­tro­duced dis­ease. For ex­am­ple, is­land foxes are sus­cep­ti­ble to ear mite in­fec­tions. They have been cur­rently treated with aca­ri­cides in an at­tempt to re­duce mite in­fec­tions and the mor­bid­ity and mor­tal­ity as­so­ci­ated with this highly preva­lent tumor. A study found that it is crit­i­cal to con­sider host den­si­ties at likely lo­ca­tions of pathogen in­va­sion when de­sign­ing dis­ease man­age­ment plans. (Coo­nan, et al., 2013; Cooper, et al., 2012; Fritzell and Harold­son, 1982; Hof­man, et al., 2015; Moore and Collins, 1995; Sanchez and Hud­gens, 2020; Vick­ers, et al., 2015)

• IUCN Red List [Link]

  Not Evaluated

Con­trib­u­tors

Karen Yang (au­thor), Col­orado State Uni­ver­sity, Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

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