Tetraoninae

Diversity

Tetraoninae is currently recognized as containing nineteen species across ten genera: Bonasa , Canachites , Centrocercus , Dendragapus , Falcipennis , Lagopus , Lyrurus , Tetrao , Tetrastes , and Tympanuchus (Persons et al., 2016). Roughly 129 subspecies of grouse are currently recognized, though this estimation is uncertain due to lack of comparative molecular genetic studies regarding subspecific relationships within Tetraoninae (Storch, 2007a). Most grouse are not considered to be threatened due to their large distributions in territory that is thinly populated by humans; however, some species have become threatened in recent decades. Gunnison sage grouse ( Centrocercus minimus ) is presently listed as Endangered; lesser prairie chickens ( Tympanuchus pallidicinctus ) are listed as Vulnerable by the IUCN, with some subspecies such as Attwater's prairie chickens ( Tympanuchus cupido attwateri ) being critically at risk (Storch, 2007b).

Geographic Range

Grouse bear a holarctic distribution wherein both the palearctic and nearctic regions host multiple genera and species, with willow ( Lagopus lagopus ) and rock ( L. muta ) ptarmigan occurring in both regions (Storch, 2007b). Phylogenetic analyses pinpoint the origins of the group in northwestern North America between the Miocene and Pliocene periods, with subsequent radiation of taxa amid the Pliocene-Pleistocene glacial cycles (Drovetski, 2003). Most species inhabit northern Eurasia and North America, with Chinese grouse ( Bonasa sewerzowi ) and greater prairie chickens ( Tympanuchus cupido ) exhibiting the most southern distribution in each respective biogeographic region (Lucchini et al., 2001). Grouse populations and ranges have declined significantly from historic levels in densely inhabited areas of central and western Europe as well as central and eastern North America, with driving factors including overhunting and habitat loss (Storch, 2007a).

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native

• Other Geographic Terms
• holarctic holarctic

Habitat

Grouse inhabit a diverse array of habitats across their extant range, including coniferous and deciduous forests, alpine areas, tundra, scrublands, and grasslands (Dimcheff et al., 2002; Drovetski, 2003; Ellsworth et al., 1995). Most species inhabit woodlands, though North American sage grouse ( Centrocercus ) and prairie grouse ( Tympanuchus ) are adapted to scrubland and grassland habitats (Ellsworth et al., 1995). Ptarmigans ( Lagopus ) inhabit ecosystems ranging from moorland to alpine and arctic tundra (Thirgood et al., 2000). Migratory behavior is exhibited by several species: willow ( L. lagopus ) and rock ( L. muta ) ptarmigans are known to migrate hundreds of kilometers seasonally, while smaller-scale activity is exhibited by Centrocercus , Dendragapus , Tetrao , and Tympanuchus species (Storch, 2007b).

• Habitat Regions
• temperate temperate
• polar polar
• terrestrial terrestrial

• Terrestrial Biomes
• tundra tundra
• taiga taiga
• savanna or grassland savanna or grassland
• forest forest
• mountains mountains

Systematic and Taxonomic History

Tetraoninae comprises a subfamily within the pheasant family Phasinidae , with genetic evidence supporting a close relationship with turkeys ( Meleagris ). The group was formerly classified as its own family-level taxonomic unit under the name Tetraonidae (Dimcheff et al., 2002; Storch, 2007b). Molecular genetic analyses of Tetraoninae members have resulted in a number of species distinctions in recent years, such as the separation of greater sage grouse ( C. urophasianus ) and Gunnison sage grouse ( C. minimus ) in 2000, as well as a number of genus reassignments of previously recognized species, the most recent being the reassignment of spruce grouse ( C. canadensis ) to its own genus from the genus Falcipennis (Persons et al., 2016; Storch, 2007b).

Physical Description

Grouse are galliform birds characterized by their feathered tarsi and the absence of spurs. Most species of grouse display substantial sexual dimorphism; males are generally larger than females - averaging nearly three times the mass of females in some species - and commonly possess colorful skin ornamentation such as wattles and cervical skin patches used for display purposes (Drovetski et al., 2006; Lebigre et al., 2007; Storch, 2007b). Several species are comprised of multiple physically and geographically distinct subspecies, with L. muta consisting of up to thirty species worldwide, though molecular genetic studies have only recently begun to clarify intraspecific relationships amongst grouse taxa (Storch, 2007b).

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful
• ornamentation ornamentation

Reproduction

Roughly half of the world's grouse species exhibit polygynous lekking mating systems, including the members of genera Centrocercus , Tetrao , and Tympanuchus . The remainder are monogamous (as seen in Tetrastes and Lagopus species) or express more generalized polygynous mating systems, i.e. members of Bonasa and Dendragapus (Storch, 2007b). In lekking species, males will perform visual and acoustic mate displays within their territory, giving rise to the onomatopoeic term "booming" for Centrocercus and Tympanuchus lek displays. Successful males may mate with several dozen females over the lekking period, while T. tetrix females appear to mate with only one male (Robel, 1966; Lebigre et al., 2007). Vegetated open habitats, such as forest clearings, heathland, and natural ridges in plains, are preferred breeding habitats in both lekking and monogamous species (Pedersen et al., 2013; Lebigre et al., 2007; Robel, 1966)

• Mating System
• monogamous monogamous
• polygynous polygynous

Grouse breed annually during a springtime mating season, with most species mating between the months of April and May (Hoppe et al., 2019; Lebigre et al., 2007; Pedersen et al., 2013; Storch, 2007b; Thirgood et al., 2000). Female grouse are capable of storing sperm for a prolonged period of time after mating, up to two weeks in T. urogallus . Egg clutch sizes generally fall in the range of 5-12 eggs and are incubated solitarily by females for 3-4 weeks until hatching (Hoppe et al., 2019; Lebigre et al., 2007; Storch, 2007b).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous
• sperm-storing sperm-storing

In most grouse species, females incubate eggs and rear chicks in the absence of male investment. Only in the willow ptarmigans ( L. lagopus ) is male parental investment common with the majority of males guarding their mates throughout the incubation period (Freeland et al., 1995; Storch, 2007). During incubation, females of most grouse species spend upwards of 90-95% of their time incubating eggs; greater prairie chicken ( T. cupido ) hens that are brooding were consistently observed to limit time away from the nest to a morning and evening foraging bout per day (Hoppe et al., 2019). As for other galliform birds, grouse chicks are precocial and capable of walking and foraging soon after hatching, though they are accompanied by their mother and reared in suitable areas until reaching independence in the following fall (Pedersen et al, 2013; Storch, 2007).

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

Lifespan/Longevity

Longevity in wild grouse remains poorly documented in literature, with age structure in wild populations and its impact on population health identified as an area of research needed by the IUCN (Storch, 2007b). In black grouse ( T. tetrix ), wild males and females between 5-6 years of age have been identified via surveys of lekking habitats (Kervinen et al., 2016; Soulsbury et al., 2012).

Behavior

Grouse species are generally terrestrial and are ground-nesting, though they are capable of flight (Storch, 2007b). During the majority of the year, grouse do not adhere to strict social organization patterns. Some species such as rock ptarmigans ( L. muta ) and black grouse ( T. tetrix ) are known to form large flocks in the winter months, with L. muta flocks being recorded to consist of ~100 individuals. Other species in this genus are solitary outside of breeding season and neither avoid nor actively seek to form conspecific groups (Lebigre et al., 2007; Pedersen et al., 2013; Storch, 2007b). During breeding season, lekking behavior is observed in about half of known grouse species, during which males will display before assembled groups of females to attract mates. Males' competitiveness and aggression, as well as the attractiveness of their display to females, are involved in reproductive success during lekking events (Robel, 1966; Sadoti et al., 2016)

• Key Behaviors
• terricolous
• flies
• diurnal diurnal
• motile motile
• solitary solitary
• territorial territorial
• social social

Communication and Perception

In lekking species of grouse, males display for females in an attempt to secure mates while also competing with rival males over territory (Sadoti et al., 2016). Lekking males are often physically larger than females and are physically ornamented because the species rely on visual cues to perceive their environments. Males of several taxa host brightly-colored combs, inflatable skin sacs, or sex-specific feather patterns. Depending on species, these may be used to display for females or exhibit competitive displays for other males (Drovetski et al., 2006; Holder & Montgomeri, 1993; Storch, 2007b). Lekking displays also often contain a vocal component, particularly in the loud "booming" lek displays seen in the males of Tympanuchus species (Robel, 1966; Sadoti et al., 2016).

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Adult grouse are generally herbivorous, though chicks are known to consume invertebrates to help supply the energy needed to sustain their rapid growth early in life (Storch, 2007a). The diets of adults are known to vary between species, with forest-dwelling species such as black grouse ( L. tetrix ) and western capercaillie ( T. urogallus ) having been found to contain Scots pine foliage in their stomach contents while rock ptarmigans ( L. muta ) consumes birch and willow buds instead. Some grassland species, such as sharp-tailed grouse ( T. phasianellus ) and lesser prairie chickens ( T. pallidicinctus ) are known to have granivorous diets (Newman et al., 2020; Storch, 2007a). Habitat structure in regard to food availability is known to play a role in habitat preference in grouse. Presence of shrub-based food resources was found to correlate positively with lek site attendance in T. pallidicinctus , with loss of foraging habitat implicated as a significant conservation threat for tundra-dwelling grouse species (Sadoti et al., 2016; Storch, 2007b).

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore
  • granivore granivore

Predation

Grouse are preyed upon by a wide range of vertebrate predators throughout their range. Red foxes ( Vulpes vulpes ) are an important predator of many grouse species with increased populations of foxes often correlating with declines in sympatric grouse species. Domestic dogs ( Canis lupus familiaris ) are also known to prey on grouse and are believed to be a significant threat to populations of caucasian grouse ( L. mlokosiewiczi ) (Storch, 2007a; Storch, 2007b). Several species of predatory birds, such as northern harriers ( Circus cyaneus ) and peregrine falcons ( Falco peregrinus ), are significant predators of both adult and juvenile grouse. Nest predation is another frequent threat to grouse. Mesocarnivorous mammals such as the American badger ( Taxidea taxus ) are recognized as frequent grouse nest predators, while nest predation by common ravens ( Corvus corax ) has been identified as a growing conservation threat to greater sage grouse ( C. urophasianus ) populations (Hoppe et al., 2019; Coates & Delehanty, 2010). The primary mode of predator defense in most grouse species is crypsis, with females commonly having camouflaged plumage (Storch, 2007b).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Grouse play important roles as prey species in their ecosystems due to a wide range of mammalian and avian predators preying upon grouse (Storch, 2007b; Thirgood et al., 2000). Grouse are also known to act as seed dispersers; seeds of poison ivy ( Toxicodendron radicans ) have been identified in the droppings of both sharp-tailed grouse ( T. phasianellus ) and ruffed grouse ( B. umbellus ), with seeds excreted by the latter germinating at statistically normal levels (Penner et al., 1999). Several grouse species are also known to act as hosts for parasitic organisms. Intestinal helminths are common in Georgian populations of caucasian grouse ( L. mlokosiewiczi ), and caecal nematodes Trichostrongylus tenuis are known to parasitize willow ptarmigan ( L. lagopus ) populations in southern Scotland, with incidences of parasitic eyeworms ( Oxyspirura petrowi ) found in 75% of a surveyed population of lesser prairie chickens ( T. pallidicinctus ) (Dunham et al., 2014; Storch, 2007b; Thirgood et al., 2000).

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Grouse have historically served as an important game animal in regions they co-inhabit with humans. Grouse hunting is conducted for both food and sport (Storch, 2007a; Storch, 2007b). In recent decades, ecotourism focused on grouse lekking sites has increased in popularity, resulting in some economic influx for communities located near leks (Storch, 2007b).

• Positive Impacts
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known adverse effects of Tetraoninae on humans.

Conservation Status

The majority of grouse species are not imminently threatened with extinction, which is common for most species possessing large ranges that oftentimes contain large tracts of thinly inhabited and/or relatively undisturbed habitats (Storch, 2007b). Of the 19 currently recognized species of grouse, two are presently ranked as Threatened by the IUCN: Gunnison sage grouse ( C. minimus ), which were classified as Endangered due to their small/fragmented ranges, small populations, and threats faced due to habitat destruction, and lesser prairie chickens ( T. pallidicinctus ), which were classified as Vulnerable due to their small population sizes, rapidly diminishing ranges, and threats faced due to habitat disruptions for agriculture and petrochemical exploration (Birdlife International, 2018; Birdlife International, 2020; Storch, 2007a). Certain subspecies of grouse are even more critically threatened, such as Attwater's prairie chickens ( Tympanuchus cupido attwateri ), which qualify as Critically Endangered with a wild population of less than 50 mature specimens (Storch, 2007a). Many conservation strategies for threatened grouse species focus on habitat preservation since habitat loss and population subdivision are recognized as eminent threats to the continued sustenance of grouse species (Storch, 2007b).

Other Comments

Fossil and mitochondrial DNA evidence suggest the origins of Tetraoninae being in the Pliocene period (~7.2 MYA) in the northwestern nearctic, with significant radiation of grouse taxa occurring between 3.2 - 1.9 MYA as a result of increased fluctuations in global climate and the appearance of new diverse habitat types in the palearctic and nearctic (Drovetski, 2003).

Additional Links

Encyclopedia of Life

Contributors

Casey Shaw (author), Colorado State University, Sydney Collins (editor), Colorado State University.

References

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