More info for the terms: avoidance, cover, density, frequency, hardwood, parturition, phenology, presence, selection, shrub, shrubs, succession, taiga, tree, tundra
In general, moose tend to select habitats that offer the highest density, highest biomass, and most nutritious forage [206,269,280]. Habitat use may be modified by weather (e.g., snow accumulation and temperature; see Cover); rutting activity; calving; presence of lick sites and aquatic habitats; predators; population density; individual age, gender, and reproductive status; and juxtaposition of habitats providing food and cover [206]. Across the moose's range in North America, important moose habitats include mature, closed-canopy conifer or conifer-hardwood forests and high forage-producing, early-successional forests, shrublands, and aquatic habitats [79,93,206]. Moose appear to require both young and old forests in their home ranges [276]. Seasonally, moose use high forage-producing, open-canopy habitats in spring and early summer and again in late fall and early winter. They shift to denser cover in late summer and in midwinter. Habitat use is largely governed by forage availability, except when severe winter weather favors use of closed-canopy forests [201].
According to a comprehensive review of moose habitats in North America, "typical" habitat providing abundant herbaceous forage and deciduous browse includes shrubby, open upland habitats—such as logged areas, burns in early succession, and subalpine shrublands—and aquatic habitats in spring and early summer [206]. Closed-canopy areas are often used in late summer for protection from extreme heat [265]. Moose return to shrubby, open upland areas—such as large stands of shrubs and saplings—in fall and early winter during the rut and prior to migration [206,265]. Closed-canopy areas—tall shrub communities or tall closed-canopy conifer and hardwood-conifer stands—are used in late winter when forage quantity and nutritive quantity is lowest and moose seek areas sheltered from snow [206]. Moose may remain in shrubby, open habitats throughout winter if snow is soft and shallow and forage remains accessible [265].
In mountainous terrain, regardless of region, moose tend to occupy subalpine forests, timberline forest-shrubland mosaics, and shrublands above timberline in summer and early fall [206,265]. Because snow depths are often less at low elevations, moose often move from high elevations in early winter to low elevations in late winter. In late fall in mountainous terrain, moose typically migrate into lowland shrubfields in old burns or logged areas or into floodplain riparian vegetation, remaining there through winter [206]. In some regions, snow depth is lower at wind-blown, high-elevation sites than at low-elevation sites, and the reverse pattern is exhibited (see Seasonal movements and migration).
In flat terrain, moose use aquatic habitats and open upland sites such as aspen and willow stands in summer. Late-winter habitat in flat terrain is usually dense conifer forest. In tundra, moose occupy riparian shrublands year-round and adjacent uplands with sparse shrubs in summer [265]. On the basis of total year-round use, shrublands, particularly willow habitats, are the most preferred habitat throughout the moose's range [200,265].
Forage: For information on moose habitat use relative to forage quantity and quality, see Forage site selection.
Cover: Moose most commonly select closed-canopy communities in late summer and late winter. They most commonly select open-canopy communities during late fall, early winter, and spring. Deep and/or crusted snow and high temperatures cause moose to seek closed-canopy habitats. Moose habitat use varies between years, reflecting differences in weather [209].
Summer: Moose may shift from open habitats in early summer to cool, closed-canopy habitats in late summer for protection from heat when temperatures may exceed maximum critical temperatures (see Physiology) [20,265]. In mixed-transitional forests on Superior National Forest, Minnesota, moose of mixed ages and genders preferentially occupied aquatic areas, young (<20 years old) quaking aspen/paper birch stands, and upland mature balsam fir stands in early summer. Of these habitats, open stands (<988 trees/ha) with short (<49 feet (15 m) tall), young trees were preferred. In mid- to late summer, "moderately stocked" upland stands of quaking aspen and paper birch and lowland stands of black spruce, quaking aspen, and balsam fir were used more than expected compared to availability, suggesting a shift away from the most open areas. In late summer, moose movements generally decreased, and moose shifted to mature stands (>50 years old) [201]. During a 3-year study in southwestern Montana, moose tended to use closed-canopy aspen and conifer forest during dry, hot summers and more open canopy cover during cool, wet summers [202].
Winter: During winter, snow depth is often a major determinant of moose distribution because it reduces forage availability and restricts movement (see Physical description). During mild winter weather, moose often use forests with patchy tree cover and shrubs, where forage is abundant. Moose shift to closed-canopy conifer habitats if snow conditions become severe [79,133]. A 1996 review reported that 14 studies indicated increased use of, and movement into, microsites with dense conifer cover when snow was deep and encrusted [20].
Moose foraging in snow. Photo courtesy of La Verne Smith, US Fish and Wildlife Service.
High overstory cover often characterizes winter habitat for moose because it intercepts snow, which lowers locomotion costs and/or increases browse availability relative to other available habitats [20,79,81,206]. In the mixed-transitional forest region of central New Brunswick, moose used open hardwood and conifer forest in January when snow was 11 to 19 inches (28-48 cm) deep. They used dense (basal area: >75 ft²/acre) conifer forest in March significantly more than available when snow was 30 to 44 inches (76-112 cm) deep (P<0.05) [267]. In northern New Hampshire, moose preferred 5- to 20-year-old logged areas during winter, only moving to areas with balsam fir cover when snow exceeded 36 inches (91 cm) [298]. In mixed-transitional forests on the Superior National Forest, moose preferred sparsely stocked clearcuts <20 years old before the rut. During the rut, they preferred mature (>50 years old) moist, lowland habitats. After the rut, moose again preferred open habitat (clearcuts <20 years old) containing abundant forage. Open habitats still were preferred in early winter, but moose gradually shifted to 40-year-old closed-canopy balsam fir-black spruce stands as snow accumulated during midwinter. In general, closed-canopy stands were used most often during severe winter conditions, whereas open forests were used during mild conditions [201]. In central Alberta, moose shifted from open lowland habitats in early winter to upland habitats with dense canopy cover in late winter because of increased snow depth in lowland areas. Lowland use was negatively related to mean monthly snow depths (r²=0.30, P<0.05) [237]. On the Upper Peninsula of Michigan, in late winter when snow was deep (>50 inches (127 cm)), moose of all ages and genders selected denser canopies at bedding sites (calves 74%, cows 66%, and bulls 52%) than available at nearby random points (P<0.002 for all variables), but no such difference was found in early winter when snow was shallow (<50 inches) [176]. In north-central Idaho when average snow depth in open areas was >30 inches (75 cm), moose movements were restricted to multicanopied old-growth forests where snow depth averaged 7 inches (18 cm) [213]. In southeastern Alaska during a winter of below-average snowfall, moose preferred hardwood stands; used conifer stands, hardwood-conifer stands, and logged areas in proportion to availability; and avoided open areas. During an above-average snowfall winter, moose used conifer and hardwood-conifer stands more, and hardwood stands and logged areas less, than in the below-average snow winter (P<0.01 for all variables) [114]. Racey and Racey [225] found that conifer species and tree spacing determined a habitat's ability to intercept snowfall and provide thermal protection for moose in southwestern Ontario. Forty-year-old black spruce stands >39 feet (12 m) tall and spaced at 11.8 feet (3.6 m) did not provide adequate protection from deep snow, but black spruce stands with 5.9-foot (1.8 m) spacing provided protection. The authors suggested that most conifer species would provide sufficient protection for moose from deep snow at 5.9-foot spacing [225].
Conifer forests most often provide late-winter cover for moose, but the amount of conifer cover in stands used in late winter appears highly variable. In southern Quebec, winter yards had a multicanopied forest structure with a wide range of canopy closures (range: 41-80%) and canopy heights (range: 30-69 feet (9-21 m)) [223]. Moose often use small pockets of conifer cover in hardwood and hardwood-conifer forests. McNicol and Gilbert (1978 cited in [78]) found that 80% of moose winter bedding sites in 10- to 15-year-old clearcuts were associated with young (1.0-3.0 inches (2.5-7.6 cm) DBH) conifer clumps. In northeastern Ontario, moose use of forest stands changed as winter progressed. In late February and late March during 2 winters, moose preferred hardwood-conifer stands over conifer stands or open areas. In late February, moose showed no preference for any particular hardwood-conifer stand type, but in late March, moose preferred hardwood-conifer stands with abundant balsam fir, which accounted for >50% of the winter diet [51]. Several researchers suggested that moose select hardwood-conifer stands in winter during periods of deep snow because these stands offer a good interspersion of forage and cover at a time when movements are limited ([51,114], Dussault 2000 cited in [71]).
Whether conifer or hardwood-conifer stands are used in winter, a juxtaposition of relatively open habitat with good forage availability next to closed habitat providing escape cover and a suitable microclimate appears important in moose habitat selection. In Denali National Park and Preserve, 96% of moose groups foraging on willows in open tundra from late May through early September were ≤164 feet (50 m) from cover of spruce forest [180]. In southeast Ontario, moose decreased browse use with increased distance from cover in 5- to 6-year-old clearcuts. Use decreased beyond 260 feet (80 m) from cover (P<0.01) [100]. In northwestern Quebec, moose home ranges were located in areas with high amounts of edge and interspersion among habitat patches [54]. Moose commonly select edge habitat apparently because of close proximity of habitats providing food and cover (e.g., [22,54,100,116,154,187,276,280]).For more information on this topic, see Logging and Burn size and shape. Bubenik [40] speculated that taiga moose and tundra moose may have different habitat juxtaposition requirements because taiga moose prefer disturbed areas for feeding and often seek escape in the forest, whereas tundra moose prefer more open areas and seek escape into the open.
Moose may not increase use of closed-canopy conifer forest when snow deepens, especially if conifer habitats do not have reduced snow cover. Schwab and others [243] reported that browse burial increased with increased conifer canopy cover in north-central British Columbia, and open, wind-exposed logged sites provided the most accessible forage to moose in winter. The authors suggested that logged areas may provide better moose habitat in winter than unlogged areas [243]. However, the authors did not determine how moose were using the different habitats. In North Park, Colorado, some moose used antelope bitterbrush and mountain-mahogany habitats on slopes where forage was exposed by wind during winter [16]. In the Susitna River floodplain in south-central Alaska, moose preferentially traveled along nonvegetated, windblown sites such as dry sloughs and frozen river channels during periods of deep snow because these areas had shallower snow than other sites (P<0.05) [49]. On the Seward Peninsula in western Alaska, moose occurred in riparian willow habitats 92% of the time in late winter. They utilized windswept areas of the river and gravel bars with shallow snow to access the linear bands of willow habitat along the river [95].
Moose may move to conifer habitats in late winter for reasons other than snow conditions, such as presence of abundant and/or nutritive forage or to avoid predators. On Isle Royale, moose moved into northern whitecedar bottomland and reduced daily movements during periods of deep snow (32-39 inches (80-100 cm)) [234]. Because average snow depth was not less in the bottomlands but was more variable, Renecker and Schwartz [231] attributed the increased use of bottomland areas during deep snow conditions to increased availability of high-quantity but low-quality browse in bottomlands. In south-central Alaska moose selected alder-willow communities during a deep snow winter, although overstory cover was often sparse because this habitat provided the greatest access to preferred willow browse [262]. Other researchers reported that conifer habitats had relatively more available, more nutritive browse than other available habitats in late winter, which likely explained moose use of these habitats. For more information this topic, see Forage site selection. In late winter, moose may be in poor physical condition (see Physical description) and be heat stressed when temperatures exceed 23 °F (5 °C) (see Physiology), another explanation for reduced movements and moose use of conifer habitats at this time.
According to a review of moose habitat use in North America, conifer cover does not appear to be a major component of moose winter habitats in regions where snow depth is usually <35 inches (90 cm) or in regions with little or no conifer cover [206]. In these areas, moose often concentrate in habitats with low overstory cover where food is abundant in winter, including river deltas and riparian zones with willows, rather than where snow is sparse [79]. In north-central Alaska, nonmigratory moose preferred river floodplains dominated by tall (>7 feet (2 m)) shrubs year-round. Moose appeared to congregate in the tall-shrub river floodplains throughout the year because of both high cover provided by the tall shrubs and abundant browse [183]. The review concluded that in deep-snow areas where conifers are absent, moose select microsites with combinations of shrub canopies and topographical situations, such as south-facing or wind-blown slopes, that reduce snow depths [206].
Age, gender, and reproductive status: Except during the rut, moose habitat use typically differs among males and females during much of the year. Spatial segregation apparently occurs because adult males select habitat with greatest forage abundance, while females—especially cows with calves in summer—select habitats with greater cover [36,177]. Miquelle and others [177] observed segregation of male and female moose in Denali National Park and Preserve and found that segregation was greatest in winter and with large bulls. The authors speculated that because of their larger body size and postrut energy deficit, large bulls were more prone to malnutrition in winter than other age or gender classes, causing them to move to areas with high forage biomass but deep snow, whereas other age and gender classes foraged in areas with low forage availability but low snow depths [177]. Many researchers reported that cows with calves sought heavier cover than other adults (e.g., [36,72,176,177,202,281]). Peek [202] noted that bulls and cows without calves made greater use of open areas than cows with calves during summer in southwestern Montana. In the Upper Peninsula of Michigan in winter, cows and calves bedded in denser eastern hemlock stands (75% canopy cover) than bulls, probably because calves needed shallower snow to avoid predators. Bull bedding sites were found in less dense balsam fir (57% canopy cover), probably because this habitat was abundant and provided some shelter as well as food [176]. In interior Alaska, males moved into a mechanically-crushed feltleaf willow opening to forage, while females and young remained in the adjacent untreated feltleaf willow habitat with less forage but more cover [36]. In Denali National Park and Preserve, females with calves tended to use quaking aspen-white spruce and resin birch-diamondleaf willow habitats during the calving-summer period (1 May-24 August) and tended to avoid habitats commonly used by males and females without calves, such as upland Richardson's (Salix richardsonii) or diamondleaf willow habitats [177]. However, in some areas such as southeastern Wyoming, males and females apparently do not segregate [16].
Predation risk: Predators may force moose to select habitats where detection by predators is less probable [75,258]. In a 1996 review, Balsom and others [20] concluded that mature conifer forest may be important to moose because it provides cover, shallower snow depths, and improved mobility, all of which can reduce predation. In southeastern British Columbia, gray wolf moose-kill sites were located farther from edges of small forest patches than random sites (P<0.05 for all variables), indicating that sites farther from cover had greater predation risk [137].
Predation risk may also influence feeding behavior of moose, with moose foraging less selectively with increased predation risk [79]. In Denali National Park and Preserve, moose foraging selectivity on feltleaf willow (based on the stem diameter at the point of browsing) decreased as distance to concealment cover of white spruce forest increased. Cows with calves, which were considered the most vulnerable to predation, fed less efficiently (spent less time foraging and more time alert) than other age and gender classes [180]. In 7- to 10-year-old postfire habitats on the Kenai Peninsula—where vegetation averaged <3 feet (1 m) tall and provided little cover for moose—moose foraged on less preferred species when they were remote from (130-200 feet (40-60 m)) concealment cover in winter [296]. In Michigan, solitary adults and yearlings selected mainland sites with abundant browse, whereas female moose with young calves chose small predator-free islands throughout the growing season even though forage conditions were poorer on the islands than on the mainland sites [75].
In most cases a combination of factors likely influences moose habitat use. In Quebec, moose distribution across the landscape appeared to be a trade-off among predator avoidance, deep snow avoidance, and food availability. At the landscape scale, moose avoided areas used by gray wolf packs, but by doing so, concentrated in areas where snow was deep. However, moose appeared to counterbalance the costs of deep snow by selecting heterogeneous landscapes where habitats providing food were highly interspersed with habitats providing cover [72].
Cover requirements:
Calving sites: Calf mobility following parturition is limited, and movements are restricted to the calving site, a small area around the birth site [37]. Maternal females typically remain at calving sites 1 to 2 weeks after birthing [141,240,275], and movements may not approach preparturition levels until 3 to 4 weeks after birthing [37,275]. In south-central Alaska, maternal moose movements increased the 2 days prior to parturition, were greatly reduced for at least the next 9 days, and did not approach preparturition levels until calves were about 26 days old [275]. Moose typically use different calving sites each year ([37,52,297], abstract by [45]).
Moose appear to select calving sites based upon forage abundance and nutritional quality (to support high energetic costs of lactation); vegetation cover and structure (to conceal neonates); reduced predation risk (seeking good vantage points such as elevated open sites from which potential predators could be sighted; areas with reduced chances for encounters with predators; or areas providing escape from potential predators such as areas near open water); or a combination of these factors [3,37,141,215,240,280]. However, calving-site selection is highly variable. Some researchers in interior Alaska [37], central Quebec (abstract by [45]), and south-central Ontario [300] found that calving sites were located at high elevation or locally elevated features such as hill tops or upper slopes, presumably from which potential predators could be sighted; however, elevation and slope position did not appear to influence calving-site selection in northern New Hampshire [240], northwestern Montana, southeastern British Columbia [141], or central Ontario [3]. Researchers in north-central Maine [151], Wyoming (Altmann 1958, 1963 cited in [141]) and northwestern Montana [52] concluded that calving sites were located close to forage and water. In interior Alaska, forage, particularly willow, was more than twice as abundant, and forage quality was slightly but significantly higher, at calving sites than at random sites (P<0.01 for all variables) [37]. However, researchers in northern New Hampshire [240], central Quebec (abstract by [45]), central Ontario [3], northwestern Montana, and southwestern British Columbia [141] found no indication of selection for water or forage.
Several researchers attributed high variability in calving site choice to differences in potential predator avoidance strategies and potential compensatory relationships among habitat variables that provide seclusion and cover [3,141,215]. In interior Alaska, Bowyer and others [37] found an inverse relationship between visibility and availability of forage, indicating that moose made trade-offs between risk of predation and food in selecting calving sites. In southeastern British Columbia moose exhibited 2 distinct calving-site selection strategies: 52% of cows calved at high-elevation sites where forage quantity and nutritional quality were low but risk of predation by grizzly bears was also low, and 48% of cows calved at low-elevation sites close to water where forage quantity and nutritional quality were high. Predation risk was also high at low-elevation sites, but moose selected low-elevation sites with relatively greater visibility [215]. Scarpitti and others [240] suggested that lack of a relationship between calving sites and forage abundance in their study was likely due to abundant food resources throughout the study area. The authors speculated that moose populations at the southern limit of the moose's distribution are unlikely to be limited by food resources, whereas moose in northern regions may have restricted food resources prior to parturition [240]. Bubenik [40] suggested that cover and visibility appeared less important on island sites where predators were absent than on mainland sites.
Aquatic habitats: In North America, particularly in eastern and central parts of the moose's range, moose commonly use aquatic habitats such as lakes, ponds, rivers, marshes, bogs, and muskegs [206,280]. Moose use aquatic habitats primarily to feed on sodium-rich aquatic plants (see Diet) [280]. Moose may also use aquatic habitats to drink water, avoid biting insects, thermoregulate, and avoid potential predators [15,86,206,258]. However, some moose populations exhibit little or no use of aquatic habitats [40,206]. Regional differences in moose use of aquatic habitats are in part related to the availability of aquatic habitats and aquatic plants within those habitats [206]. The availability of alternative sodium sources such as lick sites may also influence aquatic habitat use [86]. Through feeding activity, moose can alter density and composition of aquatic vegetation by reducing the availability of preferred aquatic plants, by trampling plants, or by increasing turbidity (see Moose foraging effects) [86,87,200].
Moose on the Kanuti National Wildlife Refuge. Photo courtesy of Bill Raften, US Fish and Wildlife Service.
Moose may forage in aquatic habitats year-round, but peak use typically occurs during late spring to fall [206]. Moose appear to begin and end use of aquatic habitats earlier in southern parts of the species' distribution [200]. MacCracken (1992 cited in [206]) reported moose use of aquatic plants throughout the year on the Copper River Delta, Alaska, with peak use occurring May through August. In Ontario, moose began feeding on aquatic plants in late May or early June and continued to feed on aquatic plants until mid-October [282]. Peak use of aquatic habitats coincides with peak moose sodium requirements—which peaks during lactation and antler growth in late spring and early summer—and with aquatic plant phenology and growth—which peak in late summer [1,86]. On Isle Royale, American beaver (Castor canadensis) ponds were frozen from November to April and thus were unavailable to moose. After spring thaw, little aquatic foliage persisted from the previous growing season, so aquatic plants were largely unavailable to moose in spring. Moose ate aquatic foliage as soon as it became available in early June and continued throughout the summer and early fall; maximum aquatic plant biomass was available to moose during late August to early September [5].
Moose select aquatic habitats where their preferred forage is abundant. In east-central Ontario, moose tended to feed in areas with abundant needle spikerush, narrowleaf bur-reed (Sparganium angustifolium), green algae (Chara spp.), Farwell's watermilfoil (Myriophyllum farwellii), and Robbins' pondweed (Potamogeton robbinsii). Moose fed primarily on these species where water flowed into the lake. The water inflow may have supplied hydrogen carbonate and calcium or increased the growth of plants favored by moose [86]. In northeastern Minnesota, American beaver ponds, slow streams, and small lakes with "mucky" bottoms had greater productivity of aquatic plants important to moose than fast streams and large lakes with rocky bottoms. The authors found that only the littoral zone (depth to <10 feet (3 m)) of large water bodies provided aquatic forage plants for moose. American beaver ponds were important sources of aquatic vegetation for moose, but aquatic plant productivity in American beaver ponds varied with pond age, with very young and very old ponds appearing least productive and thus least suitable for moose [1]. Moose on Isle Royale foraged in American beaver ponds dominated by smooth stonewort (Nitella flexilis) and pondweeds (alpine pondweed (Potamogeton alpinus) and small pondweed (P. pusillus)) where water was <4.9 feet (1.5 m) deep and substrates ranged from fine gravel to deep (<3.3 feet (1 m)) silt [5].
Lick sites: Mineral licks used by moose may occur naturally or be man-made. Some researchers consider licks critical to moose health, whereas lick absence in some locations with moose suggests that licks may not be essential on all sites [40]. Moose may use lick sites for water, mineral supplementation, and social gathering [228]. Consumption of lick water and soils may allow moose to improve rumen function and nutrient absorption during transition from low-quality, high-fiber winter diets to high-quality spring forage; to shift from high-quality spring forage to summer forage with higher concentrations of plant defense compounds; to improve palatability and digestibility of forage by absorbing tannins and toxins; to replace mineral reserves depleted during winter; and to supplement elemental intake during molt, antler growth, and nutritional stress associated with pregnancy and lactation [15,264].
Moose use licks throughout the day and night, but primarily from dusk until dawn [15,228,264]. Moose may use licks throughout the year [228,232] but use typically peaks in late spring and early summer before decreasing steadily through the end of summer. Peak lick use coincides with moose calving, molting, and antler growth. Because moose mostly visit licks before aquatic vegetation is fully developed, licks may fulfill moose's sodium requirements before other sodium sources are available [15,144,232,264]. Although moose use mineral licks more often in spring and early summer and aquatic vegetation more in summer and fall, moose visit licks regardless of availability of aquatic vegetation [149,175,232]. This may be because licks provide a more concentrated source of sodium [175,232].
Some researchers found that more females than males visited licks [15,149,175]. Miller and Litvaitus [175] proposed that greater frequency of visits to licks by females in northern New Hampshire may reflect females' greater need for sodium. In Alaska, peak lick use by bulls occurred earlier in the summer than peak use by cows. Summer molt was initiated first by adult bulls and then by cows (see Physical description) and may explain why bulls used licks earlier in the season than cows. Parturition, which confines cows and their calves to calving sites, may also delay lick use by females [264].