Grouse

Grouse/ɡraʊs/are a group of birds from theorderGalliformes, in thefamilyPhasianidae. Grouse are presently assigned to thetribeTetraonini(formerly the subfamilyTetraoninaeand the familyTetraonidae), a classification supported bymitochondrial DNAsequence studies,and applied by theAmerican Ornithologists' Union,ITIS,International Ornithological Congress,and others.
Grouse inhabittemperateandsubarcticregions of theNorthern Hemisphere, frompine foreststomoorlandandmountainside,from83°N(rock ptarmiganin northernGreenland) to28°N(Attwater's prairie chickeninTexas).
Theturkeysare closely allied with grouse, but they have traditionally been excluded from Tetraonini, often placed in their own tribe, subfamily, or family;certain more modern treatments also exclude them.Later phylogenomic analyses demonstrated conclusively that they aresisterto the traditionally-defined grouse, and they, along with the somewhat earlier-divergingkoklass pheasant, may be treated as grouse (i.e., asbasalmembers of the Tetraonini).This is reflected in some more recent circumscriptions.
Like many other galliforms, grouse are generally heavily-built birds. The traditional grouse (excluding turkeys) range in length from31 to 95 cm (12 to37+1⁄2in), and in weight from0.3 to 6.5 kg (3⁄4to14+1⁄4lb). If they are included,wild turkeytoms are the largest grouse species, attaining lengths of 130 cm (50 in) and weighing up to 10 kg (22 lb).Male grouse are larger than females, and can be twice as heavy in thewestern capercaillie(the largest of the traditional grouse). Like many other galliforms, males often sport incredibly elaborate ornamentation, such as crests, fan-tails, and inflatable, brightly colored patches of bare skin. Many grouse have feathered nostrils, and some species, such as theptarmigans, have legs which are entirely covered in feathers; in winter the toes, too, have feathers or small scales on the sides, an adaptation for walking on snow and burrowing into it for shelter. Unlike many other galliforms, they typically have nospurs,although turkeys do possess very prominent spurs.
Grouse feed mainly on vegetation—buds,catkins, leaves, and twigs—which typically accounts for over 95% of adults' food by weight. Thus, their diets vary greatly with the seasons. Hatchlings eat mostly insects and otherinvertebrates, gradually reducing their proportion of animal food to adult levels. Several of the forest-living species are notable for eating large quantities ofconiferneedles, which most othervertebratesrefuse. To digest vegetable food, grouse have bigcropsandgizzards, eat grit to break up food, and have longintestineswith well-developedcaecain whichsymbioticbacteria digestcellulose.
Forestspecies flock only in autumn and winter, though individuals tolerate each other when they meet.Prairiespecies are more social, andtundraspecies (ptarmigans,Lagopus) are the most social, forming flocks of up to 100 in winter.  All grouse spend most of their time on the ground, though when alarmed, they may take off in a flurry and go into a long glide.
Most species stay within their breeding range all year, but make short seasonal movements; many individuals of theptarmigan(called rock ptarmigan in the US) andwillow grouse(called willow ptarmigan in the US)migratehundreds of kilometers.
In all but one species (thewillow ptarmigan), males arepolygamous.  Many species have elaboratecourtship displayson the ground at dawn and dusk, which in some are given inleks. The displays feature males' brightly coloredcombsand in some species, brightly colored inflatable sacs on the sides of their necks. The males display theirplumage, give vocalizations that vary widely between species, and may engage in other activities, such as drumming or fluttering their wings, rattling their tails, and making display flights. Occasionally, males fight.
The nest is a shallow depression orscrapeon the ground—often in cover—with a scanty lining of plant material. The female lays oneclutch, but may replace it if the eggs are lost. She begins to lay about a week after mating and lays one egg every day or two; the clutch comprises five to 12 eggs. The eggs have the shape of hen's eggs and are pale yellow, sparsely spotted with brown.  On laying the second-last or last egg, the female starts 21 to 28 days of incubation. Chicks hatch in dense, yellow-brown down and leave the nest immediately. They soon develop feathers and can fly shortly before they are two weeks old. The female (and the male in the willow grouse) stays with them and protects them until their first autumn, when they reach their mature weights (except in the malecapercaillies). They are sexually mature the following spring, but often do not mate until later years.
Grouse make up a considerable part of the vertebratebiomassin the Arctic and Subarctic. Their numbers may fall sharply in years of bad weather or high predator populations—significant grouse populations are a major food source forlynx,foxes,martens, andbirds of prey.
The three tundra species have maintained their former numbers.  The prairie and forest species have declined greatly because of habitat loss, though popular game birds such as thered grouseand theruffed grousehave benefited from habitat management. Most grouse species are listed by theIUCNas "least concern" or "near threatened", but thegreaterandlesser prairie chickenare listed as "vulnerable" and theGunnison grouseis listed as "endangered". Some subspecies, such as Attwater's prairie chicken and theCantabrian capercaillie, and some national and regional populations are also in danger.The wild turkey precipitously declined before returning to abundance, even in developed areas.
The phenotypic difference between males and females is calledsexual dimorphism.Male grouse tend to be larger than female grouse,which seems to hold true across all the species of grouse, with some difference within each species in terms of how drastic the size difference is.The hypothesis with the most supporting evidence for the evolution of sexual dimorphism in grouse is sexual selection.Sexual selection favors large males; stronger selection for larger size in males leads to greater size dimorphism.Female size will increase correspondingly as male size increases, and this is due to heredity (but not to the extent of the male size).This is because females that are smaller will still be able to reproduce without a substantial disadvantage, but this is not the case with males.The largest among the male grouse (commonly dubbed 'Biggrouse') attract the greatest numbers of females during their mating seasons.
Male grouse displaylekkingbehavior, which is when many males come together in one area and put on displays to attract females.Females selectively choose among the males present for traits they find more appealing.Male grouse exhibit two types: typical lekking and exploded lekking.In typical lekking, males display in small areas defending a limited territory, and in exploded lekking, displaying males are covered over an expansive land area and share larger territories.Male grouse can also compete with one another for access to female grouse through territoriality, in which a male defends a territory which has resources that females need, like food and nest sites.These differences in male behavior in mating systems account for the evolution of body size in grouse.Males of territorial species were smaller than those of exploded lekking species, and males of typical lekking species were the largest overall.The male birds that exhibit lekking behavior, and have to compete with other males for females to choose them, have greater sexual dimorphism in size.This suggests the hypothesis of sexual selection affecting male body size and also gives an explanation for why some species of grouse have a more drastic difference between male and female body size than others.
Sexual size dimorphism can manifest itself differently between grouse and other birds. In some cases, the female is dominant over the male in breeding behavior, which can result in females that are larger than the males.
Grouse aregame, and hunters kill millions each year for food, sport, and other uses. In the United Kingdom, this takes the form ofdriven grouse shooting. The maleblack grouse's tail feathers are a traditional ornament for hats in areas such asScotlandand theAlps.  Folk dances from the Alps to the North American prairies imitate the displays of lekking males.