Migratory Herds Research Articles

Dry wildebeest carcasses in the African savannah: the utilization of a unique resource

AbstractUtilization of dry wildebeest carcasses by spotted hyaena in an African savannah setting is investigated. Four transects of varying length (3–10 km) were located in the Maasai Mara National Reserve, Kenya. Measuring carcass weight changes biweekly over a period of 9 months monitored hyaena use of dry wildebeest carcasses. Nutrient quality of dry carcasses (skin and bone) and of flesh was analysed in the laboratory using the material collected in the field. Contrary to common expectation, carcass weight change was significantly higher when the migrants were present in the Reserve than when they were absent in all transects monitored. This is thought to indicate greater carcass utilization during periods of relative prey scarcity caused by the migratory herd movements within the Reserve, and perhaps, the territorial nature of spotted hyaenas. Nutrient analysis indicated that dry carcasses contain significant amounts of protein, carbohydrates and minerals, although lacking in fats compared with flesh. The opportunistic nature and evolution of a digestive physiology in this species capable of utilizing dry carcasses appears to have important adaptive value in an environment frequented by thousands of migrant herbivores for short periods every year.

Dynamics of grazing lawn formation: an experimental test of the role of scale‐dependent processes

Grazing lawns are characteristic for African savanna grasslands, standing out as intensely grazed patches of stoloniferous grazing‐tolerant grass species. Grazing lawn development has been associated with grazing and increased nutrient input by large migratory herds. However, we argue that in systems without mass migrations disturbances, other than direct grazing, drive lawn development. Such disturbances, e.g. termite activity or megaherbivore middens, also increase nutrient input and keep the bunch vegetation down for a prolonged time period. However, field observations show that not all such disturbances lead to grazing lawns. We hypothesize that the initial disturbance has to be of a minimal threshold spatial scale, for grazing intensity to be high enough to induce lawn formation. We experimentally tested this idea in natural tall savanna grassland. We mowed different‐sized plots to simulate initial disturbances of different scales (six times during one year) and applied fertilizer to half of the plots during two years to simulate increased nutrient input by herbivores or termite activity. Allowing grazing by naturally occurring herbivores, we followed the vegetation development over more than three years. Grazing kept bunch grass short in coarser, fertilized plots, while grasses grew out toward their initial height in fine‐scale and unfertilized plots. Moreover, lawn grasses strongly increased in cover in plots with an increased nutrient input but only after coarser scale disturbance. These results support our hypothesis that an increased nutrient input in combination with grazing indeed induces grazing lawn formation, but only above a threshold scale of the initial disturbance. Our results provide an alternative mechanism for the development of grazing lawns in systems that lack mass migrating herds. Moreover, it gives a new spatial dimension to the processes behind grazing lawn development, and hence help to understand how herbivores might create and maintain spatial heterogeneity in grassland systems.

Short sampling intervals reveal very rapid root turnover in a temperate grassland

Although root growth and mortality play critical regulatory roles in terrestrial ecosystems, little is known about the temporal scale of these dynamics. In temperate grasslands, root dynamics may be particularly rapid because of the high proportion of production allocated to very fine root biomass. In this study, we used minirhizotron tubes to estimate root growth and mortality in an upland grassland in Yellowstone National Park that was grazed by migratory herds of ungulates. Monthly rates of root growth and mortality were estimated from May to September 2005, by measuring the elongation (growth) and disappearance (mortality) of roots at 3-day intervals. Average daily growth (millimeters of root length) was approximately 5 times greater in May and June than in July, August, and September. Average daily mortality (millimeters of root length) did not differ among months. A comparison of the June-September rates of root growth and mortality derived from sampling at short (3-day) and long (1-month) time intervals indicated that the long sampling intervals underestimated both growth and mortality by approximately 60% relative to the short intervals. These results suggest that estimates of grassland root dynamics from minirhizotrons are influenced significantly by sampling interval length, and that rapid root turnover may play a more critical role in regulating energy and nutrient fluxes in temperate grasslands than has previously been recognized.

Integrative use of spatial, genetic, and demographic analyses for investigating genetic connectivity between migratory, montane, and sedentary caribou herds

Genetic differentiation is generally assumed to be low in highly mobile species, but this simplistic view may obscure the complex conditions and mechanisms allowing genetic exchanges between specific populations. Here, we combined data from satellite-tracked migratory caribou (Rangifer tarandus), microsatellite markers, and demographic simulations to investigate gene flow mechanisms between seven caribou herds of eastern Canada. Our study included one montane, two migratory, and four sedentary herds. Satellite-tracking data indicated possibilities of high gene flow between migratory herds: overlap of their rutting ranges averaged 10% across years and 9.4% of females switched calving sites at least once in their lifetime. Some migratory individuals moved into the range of the sedentary herds, suggesting possibilities of gene flow between these herds. Genetic differentiation between herds was weak but significant (FST=0.015): migratory and montane herds were not significantly distinct (FST all<or=0.005), whereas sedentary herds were more differentiated (FST=0.018-0.048). Geographical distances among sedentary herds limited gene flow. Historical estimates of gene flow were higher from migratory herds into sedentary herds (4Nm all>9) than vice-versa (4Nm all<5), which suggests migratory herds had a demographic impact on sedentary herds. Demographic simulations showed that an effective immigration rate of 0.0005 was sufficient to obtain the empirical FST of 0.015, while a null immigration rate increased the simulated FST to >0.6. In conclusion, the weak genetic differentiation between herds cannot be obtained without some genetic exchanges among herds, as demonstrated by genetic and spatial data.

Camel Husbandry among Pastoralists in Darfur, Western Sudan

Introduction A summary is given of a study conducted during 2003 in the Darfur states of western Sudan. The study presents information about mainly nomadic camel owners, types of camels and other animals reared, camel herd structure, purpose of camel rearing, movement during the year, feeding, management and the economic aspects of camel husbandry. The camel (Camelus dromedaries, one-humped camel) in Darfur originated in Arab countries and was introduced to the Sudan. These camels are kept in nomadic systems in the semi-desert and savanna belt of Darfur, in association with sheep and goats. Camels produce milk, meat, wool, hair and hides and are used for riding, transport and cultivation. Nomadic Sudanese Arab tribes that own camels include Maalia, Mahria, Umm Jallol, Awlad Zaid and Bani Haiba. Other tribes of the Midob and Zaghwa also own camels. Nomadic Arab tribes and other tribes owning camels have entered Sudan through the west and north-western borders via northern Chad or southern Libya, reaching their ultimate destination at the River Nile. The problems facing camel production in Darfur states include shortage of water in desert areas, complicated inter-ethnic grazing access and diseases and parasites. In recent years these areas have been affected by drought and some areas of grazing land have been partially desertified; hence migratory herds of camels have penetrated southwards into the savannah zone for dry-season grazing. Moreover, the extension of crop farms has meant a reduction of available grazing land, which has led to serious problems culminating in the Darfur war starting in mid-2003. Arabian camels have become fully adapted to the desert and semi-desert regions of Sudan. The number of camels in the Sudan was 3.20 million (FAO 1999). The total number of camels in the three Darfur states is estimated as 759,000 of which 397,000 were in Northern Darfur, 287,000 in Western Darfur and 75,000 in South Darfur (Central Bureau of Statistics 2003). The Sudan famine of the mid-1980s caused social dislocation; many farmers and pastoralists were displaced and driven from the western provinces into urban feeding stations (Werner 1994). Similarly, the Darfur wars in 1989 and mid-2003 caused social dislocation in which most pastoralists were displaced and moved to urban areas. Hence the objectives of the present study were to estimate the socioeconomic performance of camel owners and to obtain information on camel management among the nomadic tribes of Darfur. Study Area and Methods The study was conducted from January to December 2003, mainly in South Darfur State in the extreme south-west of Sudan, an area of 139,800 sq. km between latitude 8[degrees]: 30-17[degrees]: 30 N and longitude 23[degrees]: 15-28[degrees] E. Some data from northern and western Darfur states were also included. The rainy season starts in May and continues until October, with most rain falling in July and August, and an annual mean of 400 mm (Nyala Meteorological Station 1961-2002). Temperatures reach a maximum of 42 [degrees] C in May and a minimum of 15[degrees]C in January. The rangeland is semi-desert in the north to treed savannah in the south. In recent years the area of rangeland has decreased, while the area under crops and non-agricultural activities has progressively increased. A questionnaire was used for discussions with groups of three to five camel owners, visiting Nyala livestock market at monthly intervals. Some owners were visited in their camps outside Nyala city. Records were also obtained from the towns of El Fasher and Kebkabiya (Northern Darfur State) and Sarf Umra (northern and western Darfur). Characteristics of Camel Owning Families Most of the camel owners were nomadic (77%). Due to the lack of mobile schools and the need for families to migrate, 79% of them were uneducated. Forty percent of the household heads had more than one wife, with an average household size of nine. …

Grassland regeneration and reconstruction: the role of grazing animals

Grassland regeneration and reconstruction: the role of grazing animals

Spotted hyenas (Crocuta crocuta) follow migratory prey. Seasonal expansion of a clan territory in Etosha, Namibia

AbstractThe spatial organization of one clan of spotted hyenas Crocuta crocuta in the centre of the Etosha National Park, Namibia, is described during the dry and the wet seasons. The clan comprised 11 adults and sub‐adults and occupied a territory of 160 km2 in the dry season and 320 km2 in the wet season. The dry season territory contained a low density (one animal/km2) of resident herbivores, such as gemsbok Oryx gazella, kudu Tragelaphus strepsiceros, giraffe Giraffa camelopardis, steenbok Raphicerus campestris and ostrich Struthio camelus, and a higher density of migratory species (12 animals/km2), principally springbok Antidorcas marsupialis, zebra Equus burchelli and wildebeest Connochaetes taurinus. These migratory species were the main prey of clan members. At the start of the wet season, the migratory herbivores migrated to the north‐west, resulting in a considerable decline in the density of prey in the area used by clan members during the dry season. In response to this decline in prey, clan members followed the migratory herds and shifted the focus of their activities to an area grazed by migratory herbivores during the wet season. There existed a strong spatial relationship between the hyena density and the migratory prey density in both the dry and wet season. We postulate that the considerable enlargement of the clan territory in the wet season is a response to both the migratory movements of prey and an increase in the dispersion of prey during the wet season.

Behavioral processes and costs of co-existence in female spotted hyenas: a life history perspective

We assessed the importance of three behavioral processes on the fitness of individual females as mediated via maternal care in matrilineally organized social groups of spotted hyenas Crocuta crocuta. These were maternal choice of foraging tactic, the maintenance of individual dominance rank (social status) within the adult female hierarchy, and the behavioral support provided by mothers to their daughters when daughters acquired their position in the adult female hierarchy. The effects of all behavioral processes were closely linked. Maternal care was dependent on maternal social status because high ranking females had priority of access to food, and individual maternal choice of foraging tactic was frequency – and social status-dependent when medium prey abundance provided an opportunity for such a choice. At medium prey abundance, low ranking females went on costly long distance commuting trips to forage on migratory herds outside the group territory, whereas high ranking females fed on kills within the group territory. As a consequence, offspring of high ranking females grew faster, had a higher chance of survival to adulthood, and thus high ranking females had a higher lifetime reproductive success. Daughters of high ranking females usually acquired a social status immediately below that of their mother provided they enjoyed the effective support from their mothers as coalition partners, and they gave birth to their first litter at an earlier age than daughters of low ranking mothers. Spotted hyenas are therefore an example of the ‘silver-spoon effect’. This study shows that the frequency-dependent outcome of behavioral processes can be a key determinant of maternal reproductive success in social carnivores and have a profound influence on the reproductive career prospects of offspring.

Predation risk and optimal foraging trade-off in the demography and spacing of the George River Herd, 1958 to 1993

The behavior options of feeding animals lie on a continuum between energy maximization and minimization of predation risk. We studied the distribution, mobility, and energy budgets of the George River herd, Ungava from 1974 to 1993. We arranged the annual cycle into 6 phases where we argue that the importance between the priorities of optimal foraging and predation risk change between periods. At calving, risk is more important than foraging for females but males take more risk to optimally forage. During the mosquito season, insect avoidance takes priority over risk and for&amp;not;aging. Optimal foraging takes precedent over risk in the late summer and fall and it is at this time that the herd expanded its range relative to numbers and forage abundance. In the winter (December to mid-March) animals sought restricted localized ranges with low snow cover to reduce predation risk. The spring migration of females may have increased risk during the interval the females were moving back to the tundra to give birth to their neonates on the low risk calv&amp;not;ing ground. In May, females sought early greens near treeline, which may have increased risk in order to provide maximum nutrition to their fetuses in the last weeks of pregnancy. The ancestors of the George River Herd during the Pleistocene, 18 000 yr. BP may have reduced predation risk by spacing-out in the Appalachian Mountains, removed from the major specie of the megafauna in the lowlands. With global warming, it is argued the major problem for caribou will be increased wolf predation rather than changing forage and nutritional regimes. It is essential that First Nation residents of the North maintain their option to manage wolf numbers if excessive predation in the future adversely affects the migratory herds of the Northwest Territories and Ungava.

Spatial and temporal scaling of population density and animal movement: A power law approach

Many ecological patterns are sensitive to spatial and temporal scale, but no general protocol has emerged for dealing with scale-dependence. We suggest that power laws, regularly used in the study of body size, can be applied to many such features. We used these techniques to describe two scale-sensitive aspects of caribou (Rangifer tarandus): population densities of North American herds when measured at varying spatial extents, and speeds of radiotracked individuals when observed at varying temporal resolutions. Log-log regression was applied, based on the power formula, Y= cX z. Non-isometric relationships existed for abundance versus area of the population range, but the pattern differed between groups. For sedentary caribou, animal numbers increased more slowly than spatial extent (z = 0.503). For migratory populations, this relationship was hyper-allometric (z > 1), and densities were generally lower for continental herds compared to insular Newfoundland herds living without wolves (Canis lupus). We surmise that defining population bounds may be more subjective for sedentary herds; migratory herd densities may increase with increasing population size. Distance moved versus the interval between radiolocations was also non-isometric (z = 0.551). We standardized these movements to eliminate the confounding effects of scale, enabling comparisons across seasons and populations. The power formula helps to clarify the debate over the use of ratios, where variables may change non-isometrically. Power laws may enable the synthesis of ecological patterns sensitive to scales of space and time.

Social, state-dependent and environmental modulation of faecal corticosteroid levels in free-ranging female spotted hyenas.

Little is known about to what extent the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis may be state dependent and vary in the same species between environments. Here we tested whether the faecal corticosteroid concentrations of matrilineal adult female spotted hyenas are influenced by social and reproductive status in adjacent ecosystems and whether they vary between periods with and without social stress. Females in the Serengeti National Park frequently become socially subordinate intruders in other hyena territories by undertaking long-distance foraging trips to migratory herds, whereas in the Ngorongoro Crater they usually forage inside their own small territories on resident prey. The faecal corticosteroid concentrations in Serengeti females were significantly higher than in Ngorongoro females. Energy expenditure by lactation is exceptionally high in spotted hyenas and this may be reflected in their corticosteroid levels. The faecal corticosteroid levels in both populations were higher in lactating than in non-lactating females. During periods of social stability, faecal corticosteroid concentrations increased in non-lactating females but not in lactating females as social status declined. Lactating Serengeti females had significantly higher faecal corticosteroid concentrations during periods with acute severe social stress than during periods without, indicating that the HPA axis is sensitive to social stimuli even in lactating females. So far few studies have used non-invasive monitoring methods for assessing social stress in freeranging animals. This study demonstrates for the first time, to the authors' knowledge, that corticosteroid concentrations may differ between periods with and without social stress for a free-ranging female mammal and that the modulating effect of social status may depend on reproductive status.

MODELING THE SPATIAL DISTRIBUTION OF THE ECONOMIC COSTS AND BENEFITS OF ILLEGAL GAME MEAT HUNTING IN THE SERENGETI

ABSTRACT. Illegal game meat hunting in the Serengeti National Park, Tanzania, and adjacent game reserves provides an important source of protein and cash income to local communities. We construct a profitability model that describes the spatial distribution of the economic costs and benefits of illegal hunting in the Serengeti during the late 1980s and early 1990s. Costs included capital investment in hunting weapons, WR, and the opportunity cost of hunting, WO, both held to be constants; and two spatially variable components, the logistic effort of traveling to hunting areas, WL, and the penalties incurred if arrested, WP. Benefit was the expected income from the sale of meat from resident wildlife species. The model suggests: (1) WR is the most important cost. (2) WL is the second most important cost and likely to determine the spatial distribution of hunting activity if hunters seekto minimize costs. (3) WO and WP are of minor importance, the former because alternative sources of income provide low pay, the latter because the overall chance of being arrested is low. (4) WP exceeds WL only in areas close to the boundary of protected areas. (5) Although resident wildlife contributes only a minor share of illegal offtake compared to the migratory herds, hunting resident wildlife is profitable in 68% of the area. This suggests that hunting of resident and migratory wildlife is highly profitable and may explain why the utilization of the target populations has become increasingly unsustainable.

A seasonal feast: long‐term analysis of feeding behaviour in the spotted hyaena (Crocuta crocuta)

SummaryThe feeding behaviour of the Talek clan of spotted hyaenas in the Masai Mara National Reserve, Kenya, was monitored continuously for 7 years. Talek hyaenas adapted to large temporal variations in prey abundance by being opportunistic predators. During the first half of the year, the hyaenas fed on resident ungulates, and their diet consisted mainly of topi and Thomson's gazelles. Upon arrival of the migratory herds of wildebeest and zebra from the Serengeti, Talek hyaenas switched to feeding on the wildebeest which provided them with a superabundance of food for about 3 months. After the migratory animals returned to the Serengeti, Talek hyaenas experienced a period of reduced prey abundance due to the temporary dispersion of resident ungulates. At this time hyaenas hunted the few remaining wildebeest, and also increased their use of the remaining resident animals. Although Talek hyaenas were generally opportunistic in their feeding behaviour, they did exhibit clear dietary preference for larger prey species, particularly wildebeest. Finally, carrion comprised only 5% of the biomass consumed by Talek hyaenas, the lowest proportion of carrion in the diet of any Crocuta population studied to date.

Defining the Pen Islands Caribou Herd of southern Hudson Bay

In this paper, we describe the Pen Islands Herd of caribou, the largest aggregation of caribou in Ontario (it also occupies a portion of northeastern Manitoba). Photographic counts showed the herd had a minimum population of 2300 in 1979, 4660 in 1986, 7424 in 1987 and 10 798 in 1994. Throughout the 1980s, the Pen Islands caribou exhibited population behaviour similar to migratory barren-ground caribou herds, although morphology suggests they are woodland caribou or possibly a mixture of subspecies. The herd had well-defined traditional tundra calving grounds, formed nursery groups and large mobile post-calving aggregations, and migrated over 400 km between tundra summer habitats and boreal forest winter habitats. Its migration took it into three Canadian jurisdictions (Ontario, Manitoba, Northwest Territories) and it was important to residents of both Manitoba and Ontario. It is clear that the herd should be managed as a migratory herd and the critical importance of both the coastal and variable large winter ranges should be noted in ensuring the herd's habitat needs are secure.

Evolving perspectives on caribou population dynamics, have we got it right yet?

The roles of food, weather and predation are compared between sedentary and migratory caribou herds. Sedentary herds disperse (space out) at calving time while the cows of migratory herds move in masse (space away) to calving grounds to reduce predation risk. The sedentary ecotype calves on ranges near open water if tree cover is present or in rugged topography in the absence of tree cover. The migratory ecotype aggregates on calving grounds located on alpine mountain plateaus or on the tundra north of the Arctic tree line. The two herds with the greatest densities in North America, the sedentary Slate Islands Herd and the migratory George River Herd both had changes in abundance that followed summer food problems. The hypothesis that winter lichen supplies determine abundance and set the carrying capacity is rejected. Lichens are not a necessary food for caribou. A review of the mortality of young calves documented in the past 30 years provides no support for the hypothesis that hypothermia is a common mortality problem. Young calves documented can be born inviable at birth if their dams are severely malnourished. The migratory caribou in North America reached peak numbers in the 1980s after wolf populations were heavily harvested in the 1970s. The sedentary ecotype is frequently regulated by wolf predation that affects both recruitment (R) and the mortality of adults (M). The balance between R/M schedules commonly occurs when R (calves) represents, about 15% of the herd and when numbers (prorated to the area of the dispersed annual range) approximate 0.06 caribou/km2. Population limitation of migratory herds by predation has occurred in the NWT and in several herds in Alaska but only when wolf densities were &amp;gt; 6.5/1000 km2. Wolf predation halted the growth of the George River Herd in 1980 but then wolves contracted rabies and the herd again increased and degraded spring/summer ranges. The reduced summer phytomass resulted in lower birth rates and increased the vulnerability of calves and possibly adults to wolf predation. Stabilizing mechanisms for migratory herds include movements between herds above tree line and range contractions/expansions with resultant changes in demography. It is hypothesized that the most important ecological variable in all seasonal distributions of caribou is predation risk rather than to maximize forage supplies.

Post-calving photo-census of the Rivière George caribou herd in July 1993

A photographie census of the Rivi&amp;egrave;re George caribou herd in Quebec and Labrador was conducted between 4-23 July 1993 during the post-calving period. The primary objective of the study was to obtain an accurate estimate of the current size of the herd to permit the monitoring of population trends and effective management of the herd. The census procedure consisted of (1) use of satellite and conventional radio-telemetry to locate and photograph post-calving aggregations during the period of optimal aggregation, (2) determination of the minimum population size by direct counts from photographs, and (3) estimation of the total population size using the Petersen Index method. This method allowed extrapolation of the data to caribou that were either not photographed or that were not aggregated at the time of the census. The minimum count indicates that the Rivi&amp;egrave;re George caribou herd consisted of at least 358 460 adults (older than calves) at the time of the census. This count underestimates the total population size but is useful because it is virtually free of error. The total size of the Rivi&amp;egrave;re George herd in July 1993 was estimated to be 540 040 adults within 90% confidence limits of + 12.8%. Comparisons with previous estimates indicate that the size of the herd continues to be large, but that its growth has probably ceased. This study demonstrates that a photographic survey of post-calving aggregations is an effective method to census the Rivi&amp;egrave;re George herd and possibly other large migratory caribou herds that are monitored by telemetry.

The commuting system of Serengeti spotted hyaenas: how a predator copes with migratory prey. II. Intrusion pressure and commuters' space use

Abstract. In the Serengeti, Tanzania, spotted hyaenas, Crocuta crocuta Erxleben, regularly left their clan's territory to feed on the nearest migratory herds ('commuting trips'). The mean commuting distance was 40 km. Commuting locations matched the movements of the migratory herds throughout the year. The distribution of commuters was compatible with the hypotheses that commuters (1) minimized contact with resident clans and (2) utilized areas where they were assured of locating migratory herds. The proportion of clan members commuting declined as prey abundance in the clan's territory increased. Territories were visited by non-residents (commuters) throughout the year but the number of foraging commuters increased substantially when large migratory herds entered a territory. During encounters between residents and intruders, residents adjusted their behaviour according to the context of the encounter: residents ignored commuters 'in transit', responded aggressively to commuters at kills, and engaged in prolonged clashes with neighbouring clans. A comparison with the space use systems of other carnivores indicates that the commuting system of spotted hyaenas in the Serengeti is unique. It is hypothesized that the development of the commuting system was contingent on several adaptive behavioural, morphological and physiological specializations.

The commuting system of Serengeti spotted hyaenas: how a predator copes with migratory prey. I. Social organization

Abstract. The social organization and space use of spotted hyaenas, Crocuta crocuta Erxleben, in the Serengeti, Tanzania is described. In contrast to Kruuk (1972, The Spotted Hyena. Chicago: University of Chicago Press), spotted hyaenas in the Serengeti live in large stable groups (clans); median clan size for seven clans was 47 adults and subadults. Clans defended permanent territories that contained the communal den. The size of one well-known territory was 55·5 km 2. Territories contained low densities of resident herbivores (mean 3·3 animals/km 2) throughout the year, but experienced very high densities (mean 219 animals/km 2) of migratory herds, principally wildebeest, Connochaetes taurinus , zebra, Equus burchelli, and Thomson's gazelle, Gazella thomsoni, for only 26% of the year. The most important prey killed inside territories were migratory species. When the migratory herds were away from a clan's territory, clan members regularly left the territory to forage on nearby migratory herds ('commuting trips'). Clan sizes were maintained above the carrying capacity of the territory, estimated from populations of resident herbivores, by year-round exploitation of migratory herbivores. This suggests that, in contrast to many other carnivores, group sizes of Serengeti hyaenas are not limited by resources on the territory and feeding ranges are decoupled from territoriality.

Dispersal in Female White-Tailed Deer

Seven of 35 yearling female white-tailed deer ( Odocoileus virginianus ) in a migratory herd in northeastern Minnesota dispersed 18–168 km from natal ranges during late May through June. Dispersal as a proximate event appears voluntary and independent of deer density.

Temporal, Spatial, and Age-Specific Changes in Genotypic Composition of Mule Deer

Spatial, temporal, and age-specific genetic variation is described for a mule deer ( Odocoileus hemionus ) herd from northwestern Colorado during 1983—1986. Little genetic differentiation was observed between major migratory herd subdivisions, although spatial structuring and inbreeding within subdivisions is indicated during some years. Significant differences in common allele frequencies at six of 11 variable loci and changes in apportionment of genetic variance among individuals within and among locations occurred during 4 years of study. Common allele frequencies increased with year of study. Significant differences in allele frequencies also were observed between fawns and adult females. Temporal and age-specific genetic differences probably were influenced most by changes in breeding structure.