Seasonal Movements, Habitat Selection, and Food Habits of Black Bears in Shenandoah National Park, Virginia. (Nathan Garner, Master's thesis, 1986.)

ABSTRACT

This study took place from May 1982 through April 1985. 47 bear (25 adult females, 17 adult males, and 5 subadult males) were radio-collared and followed. Subadult males had the largest home ranges (289 sq km), then adult males (116 sq km), followed by adult females (22 sq km). Extensive overlap between sexes and age groups occurred. Females with cubs were more limited in the spring (but not by the fall). Large fall ranges corresponded to the dispersed mast crop compared to the summer soft mast. Adult and subadult males had less stable home ranges than adult females. Males roamed outside the Park in spring and fall and were outside the Park 17% more often than females. Males avoided park roads throughout the year, while females preferred fire roads during the summer and early fall, but avoided heavier traveled light duty roads and primary roads. Both males and females preferred foot trails. Bears rarely came within 300 feet of campgrounds, picnic areas and other human visitation sites. Both sexes used low elevations during the summer and higher elevations during early and late fall. Bears made most use of stream corridors during drier, hotter months of summer.

Twelve stomachs and 854 bear scats were examined with plant material making 90% of the annual diet and animal matter making up 8%.

Males were found in black locust/black cherry forests more than expected while being found in tulip poplar forests less often than forest composition would expect. Females used the tulip poplar forest more than males and used the black locust/black cherry forests less than males. Shifts in the use of chestnut oak/northern red oak and northern red oak/white oak forests corresponded to available mast, preference for white oak acorns, foraging strategy, and the importance of mountain laurel shrub cover in late fall.

Seasonal use of domestic fruits at 330 abandoned homesites within the Park was evaluated. While females tended to locate near the orchards more than males in summer, both sexes utilized the resources in late fall, being an important nutritional food for black bears in relation to total soft fruits eaten.

(This study was part of a comprehensive study of black bear in the SNP, done simultaneously with Dan Carney -see his Masters thesis, also included. The study area is the Central District of the SNP.)

RESULTS AND DISCUSSION

A total of 47 collared bear were located a total of 3973 times during the study. Males were located from the ground every 5-6 days whereas females averaged 3-4 days between ground locations. Males and females averaged 7-8 days between aerial locations.

Total Home Range Males had an average home range of 116 sq km and females 22 sq km. This agrees with existing studies which indicate the larger males need larger areas due to greater metabolic requirements. Further, males increase their reproductive success by being highly mobile and breeding with many females, while females only cover a minimum area necessary for "self maintenance and development of their young."

Subadults had larger home ranges than both adult sexes (289 sq km), in agreement with existing studies, as adult males caused the dispersment of the subordinate males. (One subadult, tagged as part of this study, was captured outside Baltimore in the fall of 1982.) Home range is a function of the nutritional quality of the forest. Highly diverse habitats enable bears to switch food sources in times of specific food shortages. This is the case for the SNP.

Seasonal and Annual Home Range Although some studies show an increase in male home range during the breeding season, no seasonal differences were found here. Females with cubs were more limited in spring and one of the two summers than solitary females. By fall, cubs did not limit female range. (PA found females with cubs had a larger home range than solitary females, TN, the opposite.) All bear had a larger fall home range due to the distribution of mast sites. Of the two subadult males and two females with yearlings active throughout the winter, all made use of mountain laurel thickets for protection. (Females with yearlings were the most active in PA studies.) These two groups are the most likely to need to be active, as their nutritional needs of body growth and raising young are the most demanding. Limited 24 hour studying in this study indicates bears are more diurnal in summer in search of soft mast, and more nocturnal in fall, searching for hard mast, which often takes them outside of the Park. This is in agreement with studies in the Smokies.

Home Range Stability Males generally have less stable ranges than females. Core areas within home ranges change with the seasons. This fall change, in response to hard mast, is more evident with adult females than males.

Home Range Overlap Extensive overlap occurred among adult male and female as well as subadult female home range. This is found throughout the country. Thus, some tolerance is implied among bear, with a lack of territoriality. Adult male home ranges overlap several females during the breeding season (summer). This allows the polygamous males to breed with several females. Home range overlap between adult females, subadult males and subadult females may be the result of kinship. Spatial distribution of food may also account for the overlap and tolerance. Adult female overlap was greater, and home ranges smaller, in winters of heavy mast than winters of low mast. Even with small home range and large overlap, existing studies suggests that close encounters are uncommon due to most activities of bears being limited to small areas within their home range. Strong mutual avoidance was noted among bears in the Smokies. Overlap in this study was wide ranging, with up to 96 % of total home range overlap in some cases for females. One study revealed that, outside the breeding season, a minimum of 50km was kept between adult males and females.

Seasonal Movements

Park vs non-Park. Males made long excursions to the Piedmont Plateau in the spring and early fall, but stayed in or adjacent to the Park 94% of the time during the breeding season. Females rarely ever traveled out to the Piedmont. Females were found outside the Park most in summer (21%), followed by early fall, spring and late fall (16%, 10%, and 8% respectively). All bears used the Park in late fall for acorn consumption and for winter denning. Both males and females were found outside the Park in late fall and early winter, thus exposing both to hunting pressures. However, females enter their winter dens earlier than males, thus limiting their vulnerability. Annually, males were outside the Park 32% of the time, while females were outside the Park 15% of the year.

Geographic Features. Males avoided park roads throughout the year, while females preferred fire roads during the summer and early fall, but avoided heavier traveled light duty roads and primary roads. Wild black cherries along fire roads during late summer and early fall were used extensively by bears, with females being most common users. This could, in part, be explained by noting the limiting climbing abilities of the larger male bears. (Heavy male bear can actually lose their climbing abilities.)

Both males and females showed the greatest use of small rivers and streams during the summer. SNP forests have lush vegetation along stream corridors. Males were never found within 300 feet of campgrounds or picnic areas. Only one female was found within this 300 foot area. Females were found closer to human disturbances than males throughout the year. Bear were found at lower elevation in summer (in part due to abandoned homesite orchards) and higher elevation in early and late fall, in response to mast. Ridgetop trails were used by bear more often than expected.

FOOD HABITS AND HABITAT SELECTION

Radio-marked bears were monitored during all seasons from initial capture (post spring, 1982) through April, 1985. Scats and stomachs were analyzed from May 1982 through Dec 1984, although most of the 854 scat samples were collected in 1983.

Seasons were spring (Mar 20- June 15), summer (June16-Aug 31), early fall (Sept 1-Oct 15), late fall (Oct 16-Dec 20), and winter (Dec 21- Mar 19).

Seven forest types were identified:

  1. Chestnut oak/red oak
  2. Tulip poplar
  3. N. red oak/white oak
  4. Hardwood mixture

5. Pine

6. Black locust/Black cherry

7. Hemlock

Seasonal Food Habits

Plant Foods - Tree fruits, forbs, squawroot composed 81% of the annual diet. The remaining vegetable matter included shrub and vine fruits, corn and graminoids. This is consistent with PA studies and many others throughout the country. In early spring, males would feed on cornfields outside the Park, while females would join males in summer and early fall. Males would travel further from the Park in search of corn fields than females. Certain males did this in a routine fashion.

Animal Foods - Invertebrates make up 5% while mammals and birds make up 3% of the annual diet, supplying needed protein to the diet. Vespids (yellow jackets, wasps and hornets), ants and beetles are a part of the seasonal diet (5% of the annual diet). Deer can be a major food source in winter as carrion, or, as was witnessed, a bear can run down a fawn. Trace amounts have been identified as groundhogs, opossum, raccoon, weasel, beaver, and grouse.

Spring - Primarily leaves, stems, roots, and fruits of various forbs, including sweet cicely, jack-in-the pulpit, mayapple and angelica. Intensive use of sweet cicely (46% volume) was found consistent with Montana, but not found elsewhere in the SE U.S. Jack-in-the-pulpit was second in volume with 29%, and mayapple third with 7%. Unlike the Smokies, serviceberries were not used in significant amounts (14% for the Smokies, <1% for this study, due to their sparse abundance). Forbs were a major food source for the bear. (In Washington, spring was a "negative foraging period" for black bear, that actually lost weight in the spring. This was also noted in the Smokies and Montana.) Mayapples are the main spring fruit, with sweet cherries starting at the end of spring. These are both much more nutritious than high cellulose herbaceous leaves and stems, which are hard for bears to digest because their stomachs are too acid to support the microbes needed for cellulose digestion. Ants, beetles, wasps and hornets eaten in late spring was also a good source of protein.

Summer - Forbs soon shifts to squawroot (40%), ants (11%), domestic apples (7%) and sweet cherries (5%) from old orchards. Spicebush, blueberries and huckleberries accounted for 7%. (In the Smokies, blueberries and huckleberries were 23% of the total summer diet.) Blackberries and raspberries made up another 4%. (Compared to 12-24% of the Smokies.) Yellow jackets, wasps and hornets make up another 2% of the summer diet.

Early Fall - Foods were primarily soft and hard tree fruit. Black cherry led with 48% by volume, mainly in September, like the Smokies. Black cherry was a factor in PA as a summer food. Acorns made up 19% the first two weeks of September, and most extensively used the first two weeks of October. Other hard tree fruit included apple (7%), spicebush (3%), huckleberry, blueberry, serviceberry and blackberry. Soft tree fruit included pokeberries (2%), and wild grapes (2%). (Note that the use of spicebush is the only reported case of this happening in the Appalachian mountains.)

Late Fall - Acorns (66%) and hickories (9%), apples (7%), grapes (5%), and pokeweed (1%). Since chestnut oaks failed to fruit during the study, most of the acorns were northern red oak and white oak. Successful birthing and rearing of cubs is a function of the fatty layer put on from the fats and carbohydrates consumed by fall acorn digestion. Numerous studies show a direct correlation between poor mast years and a reduction in next years cub production and subadult survival.

Winter - The few insomniacs of winter (17 scats) fed on acorns (58%) and apples (17%). Dried graminoids are used in an increased amount in early fall as material used in forming the fecal plug. Deer makes up 13%, primarily as road kills or gunshot victims.

SEASONAL HABITAT USE

1311 location sites of the 44 collared bear were observed. This represented 80% of the total number of habitat use locations; the rest were outside of the Park.

Spring - Compared to the relative abundance of the seven forest types in the Park, the females used each of the seven in proportion to their abundance, males used tulip poplar proportionately less. Females used tulip poplar forests more than males and males used black locust/black cherry more than females. The attraction of bear to these two forest types is likely related to the lush understory of forbs.

Summer - Use of forest types during the breeding period did not change. Males and females were noted together for several days. Chestnut oak/Red oak was the most used forest type, due to the parasitic plant, squawroot.

Fall - Clearly, bear use the oak forests in early and late fall predominantly. Locust /cherry forests were used more than their proportions in early fall by both males and females and in late fall by males. Young females have distinct advantages over males in familiarity with fall food sources due to the overlap that females offspring have with their mothers and the dispersal behavior of young males into unexplored areas. Exclusion of subadults and young from prime feeding sites by the adult males, seen in some studies, was not observed here. In fact, females with and without cubs were seen feeding near adult males in areas with abundant mast. During the fall, males were outside the Park 25% of the time, and females, 12% of the time. This also reduced contact among bear. Chestnut oaks failed all three years of the study, thus, the red and white oak forests were the most visited. In 1982 and 1984, white oaks had a poor mast production. White oak acorns are preferred, probably due to the low tannin levels, thus, higher palatability. (Studies of squirrels also showed the same preference.) In 1982, with poor mast, other food sources were used, such as cherries, apples, wild grapes and hickory nuts. Chestnut oak/red oak forests are heavily used in late fall due to the frequent mountain laurel cover that is associated with this forest type (after the leaf drop). Male use was 74%, and female use was 64%. During all three years, regardless of mast production, this use of the chestnut oak/red oak forest type was clear. (These chestnut oak/red oak forest types have 72% of the mountain laurel cover; the red oak/ white oak forest has only 8% of the mountain laurel cover.

Summary and Conclusions

Black bears in SNP were largely herbivorous and used seasonally abundant foods. The major food items consumed were herbaceous leaves and stems in spring; squawroot, tree fruits (sweet cherry, black cherry, apple), insects, and various forbs in summer; and tree fruits (acorns, black cherries, apple, hickory nuts) in fall. Winter-active bears relied upon acorns, apples, and white-tailed deer. Bears in SNP consumed more tree fruits (48% volume) than any other food item annually. Implications from carrion consumption seen in this study are that bears are opportunistic and will readily eat meat when it is available. Based on existing studies in NC and TN, spring foods, (forbs, grasses) in SNP were low in nutritional value; summer and early fall foods were high in sugars and other carbohydrates (fruits and seeds) and provided a source of high quality protein (animal matter); and late fall foods were high in fats and available energy (acorns).

Females preferred poplar forests for consumption of forbs in spring and early summer and for utilization of domestic apples and sweet cherries at abandoned homesites throughout summer. Males preferred locust/cherry forests for use of forbs in spring and for the consumption of wild black cherries and apples in fall. Significant shifts in use of chestnut oak/red oak and red oak/white oak forests by both males and females in early and late fall was attributed to availability of oak mast, preference for white oak acorns in early fall, foraging strategy, and the utilization of mountain laurel shrubs for escape and thermal cover in late fall.

Chestnut oak/red oak forest was the most heavily used forest type during all seasons by both males and females; it provided forbs in spring, squawroot in summer, and acorns as well as mountain laurel shrub cover in fall. The importance of oak forests in SNP in providing year round foods is added evidence that oak types are critical habitats for bears (as has been shown in various studies throughout the southern Appalachians.)

USE OF ABANDONED HOMESITES

330 homesites were identified within the Central District. Disturbed areas around the homesites averaged 1-2 ha size and included 2-3 fruit tress or small orchards (usually 5-15 trees). By far, the most common fruit trees were sweet cherry (Prunus avium) and domestic apple. 90% of the homesites had at least one of these present. Peach, pear, and plum were found at only 5% of the homesites. (In the North and South Districts, orchards were found not associated with homesites---not the case in the Central---all sweet cherry and domestic apple trees were found by homesites.)

Movements - Among males, bear showed no affinity for the orchards. In late fall, males were found less than land use would figure, due to mast in higher elevations (only 19% of homesites found in oak forests). Females tended to be found more often near homesites than would be expected by land use in the summer and early fall, and farther away in the late fall (for the same reason as males).

Phenology and Food Habits - Sweet cherries were consumed in summer (mid-June to Mid-July) when ripe, while apples were eaten in the summer, early and late fall (late fall was fallen fruit). Of the total soft fruit eaten by bears, 16, 11 and 44% of it was domestic fruit for summer, early and late fall.

Discussion - While males have larger home ranges, females tend to stick near the domestic fruit trees in their smaller ranges. "Positive reinforcement" may explain the females repeated use of the fruit trees.

Ecological Implications - Over the next twenty years, (this written in 1986), a drastic decline in fruit production can be expected as the forest takes over the fruit trees. As a result, it may be expected that bears will use commercial orchards adjacent to SNP to a greater extent.