Changes In Home Range Size Research Articles

Movement behavior in a dominant ungulate underlies successful adjustment to a rapidly changing landscape following megafire

BackgroundMovement plays a key role in allowing animal species to adapt to sudden environmental shifts. Anthropogenic climate and land use change have accelerated the frequency of some of these extreme disturbances, including megafire. These megafires dramatically alter ecosystems and challenge the capacity of several species to adjust to a rapidly changing landscape. Ungulates and their movement behaviors play a central role in the ecosystem functions of fire-prone ecosystems around the world. Previous work has shown behavioral plasticity is an important mechanism underlying whether large ungulates are able to adjust to recent changes in their environments effectively. Ungulates may respond to the immediate effects of megafire by adjusting their movement and behavior, but how these responses persist or change over time following disturbance is poorly understood.MethodsWe examined how an ecologically dominant ungulate with strong site fidelity, Columbian black-tailed deer (Odocoileus hemionus columbianus), adjusted its movement and behavior in response to an altered landscape following a megafire. To do so, we collected GPS data from 21 individual female deer over the course of a year to compare changes in home range size over time and used resource selection functions (RSFs) and hidden Markov movement models (HMMs) to assess changes in behavior and habitat selection.ResultsWe found compelling evidence of adaptive capacity across individual deer in response to megafire. Deer avoided exposed and severely burned areas that lack forage and could be riskier for predation immediately following megafire, but they later altered these behaviors to select areas that burned at higher severities, potentially to take advantage of enhanced forage.ConclusionsThese results suggest that despite their high site fidelity, deer can navigate altered landscapes to track rapid shifts in encounter risk with predators and resource availability. This successful adjustment of movement and behavior following extreme disturbance could help facilitate resilience at broader ecological scales.

Evaluating mountain lion diet before and after a removal of feral horses in a semiarid environment

AbstractNon‐native species can affect ecosystems by influencing native predator‐prey dynamics. Therefore, management interventions designed to remove non‐natives may inadvertently lead to increased predation on native species. Feral horses are widely distributed throughout the arid parts of western North America. A growing body of research indicates that horses can be an important prey species to mountain lions in ecosystems where they overlap. In December 2020, the Bureau of Land Management removed 455 horses from the Delamar Mountains, Nevada, USA. We leveraged this management intervention to implement a before–after–control–impact study to test hypotheses about predation on horses and native ungulates. We predicted (1) that horses would comprise an important part of the diet in this mixed‐prey community, (2) following removal, the proportion of horses in the diet would decrease and native ungulates would increase, and (3) mountain lion home ranges overlapping the treatment areas would increase in response to decreased prey availability. From 2018 to 2022, we investigated 1360 clusters from 29 GPS‐collared lions and identified 1056 prey items. To model the probability of a predation event (a kill), we fit a mixed‐effects logistic regression model for ungulate prey as a function of lion sex, treatment area (in/out), and treatment period (pre‐/post‐removal). We used a log‐linear regression model to evaluate changes in home range size. The most common prey were mule deer (55%), feral horses (32%), and coyotes (4%). Twenty‐two of 29 lions consumed horses, although the rate of horse consumption was highly variable across individuals. Horses of both sexes and all age classes were predated. In contrast to predictions, our models detected no effect of removals on diet composition (βinteraction = 0.30 ± 1.1), nor did the removal influence home range size (βinteraction = 0.02 ± 0.02). Despite a 46% reduction in horse abundance, we found no evidence for prey‐switching following the horse removal treatment. Removal magnitude, rapid horse immigration, and/or behavioral specialization of individual mountain lions may help explain these results. Our findings have important implications for mountain lion and feral horse management in arid environments characterized by high prey diversity, but low prey abundance.

No evidence for the consistent effect of supplementary feeding on home range size in terrestrial mammals.

Food availability and distribution are key drivers of animal space use. Supplemental food provided by humans can be more abundant and predictable than natural resources. It is thus believed that supplementary feeding modifies the spatial behaviour of wildlife. Yet, such effects have not been tested quantitatively across species. Here, we analysed changes in home range size owing to supplementary feeding in 23 species of terrestrial mammals using a meta-analysis of 28 studies. Additionally, we investigated the moderating effect of factors related to (i) species biology (sex, body mass and taxonomic group), (ii) feeding regimen (duration, amount and purpose), and (iii) methods of data collection and analysis (source of data, estimator and spatial confinement). We found no consistent effect of supplementary feeding on changes in home range size. While an overall tendency of reduced home range was observed, moderators varied in the direction and strength of the trends. Our results suggest that multiple drivers and complex mechanisms of home range behaviour can make it insensitive to manipulation with supplementary feeding. The small number of available studies stands in contrast with the ubiquity and magnitude of supplementary feeding worldwide, highlighting a knowledge gap in our understanding of the effects of supplementary feeding on ranging behaviour.

Investigation of optimized observation periods for estimating a representative home range of free-roaming domestic dogs

Free-roaming domestic dogs (FRDD), as vectors of zoonotic diseases, are of high relevance for public health. Understanding roaming patterns of dogs can help to design disease control programs and disease transmission simulation models. Studies on GPS tracking of dogs report stark differences in recording periods. So far, there is no accepted number of days required to capture a representative home range (HR) of FRDD. The objective of this study was to evaluate changes in HR size and shape over time of FRDD living in Chad, Guatemala, Indonesia and Uganda and identify the period required to capture stable HR values. Dogs were collared with GPS units, leading to a total of 46 datasets with, at least, 19 recorded days. For each animal and recorded day, HR sizes were estimated using the Biased Random Bridge method and percentages of daily change in size and shape calculated and taken as metrics. The analysis revealed that the required number of days differed substantially between individuals, isopleths, and countries, with the extended HR (95% isopleth value) requiring a longer recording period. To reach a stable HR size and shape values for 75% of the dogs, 26 and 21 days, respectively, were sufficient. However, certain dogs required more extended observational periods.

Predator-mediated interactions through changes in predator home range size can lead to local prey exclusion.

The strength of indirect biotic interactions is difficult to quantify in the wild and can alter community composition. To investigate whether the presence of a prey species affects the population growth rate of another prey species, we quantified predator-mediated interaction strength using a multi-prey mechanistic model of predation and a population matrix model. Models were parametrized using behavioural, demographic and experimental data from a vertebrate community that includes the arctic fox (Vulpes lagopus), a predator feeding on lemmings and eggs of various species such as sandpipers and geese. We show that the positive effects of the goose colony on sandpiper nesting success (due to reduction of search time for sandpiper nests) were outweighed by the negative effect of an increase in fox density. The fox numerical response was driven by changes in home range size. As a result, the net interaction from the presence of geese was negative and could lead to local exclusion of sandpipers. Our study provides a rare empirically based model that integrates mechanistic multi-species functional responses and behavioural processes underlying the predator numerical response. This is an important step forward in our ability to quantify the consequences of predation for community structure and dynamics.

Ontogenetic changes in green turtle (Chelonia mydas) diet and home range in a tropical lagoon

Ontogenetic changes in habitat and diet are widespread among marine species. Most species of sea turtles are characterized by extreme ontogenetic changes in habitat use and diet, with large changes occurring in early developmental stages (e.g., neonates to juveniles). Changes can continue even after recruitment to shallow coastal habitats. In places where substantial transitions in habitat occur across short distances, it is possible that the distances of developmental movements from one habitat to another could be short. We investigated ontogenetic changes in home range size, home range location and diet of Chelonia mydas in a tropical coastal lagoon in north-western Australia by combining acoustic telemetry with stable isotope analysis. There was a substantial (but nonlinear) increase in home-range size (kernel utilization distribution: KUD) with length, and an increase in the average distance of the center of home ranges from shore with length: larger turtles tended to occupy larger areas further from the shore. These patterns were accompanied by complex nonlinear changes in δ13C, δ15N and δ34S of red blood cells and nails; changes were rapid from 36 cm (the length of the smallest individual captured) to 50 cm, before reversing more gradually with increasing size. δ15N and δ34S (but not δ13C) of red blood cells and nails increased monotonically with KUD and distance from shore. Seagrass was likely an important food for all sizes, macroalgae was potentially important for small (< 60 cm CCL) individuals, and the proportion of scyphozoan jellyfish in diet increased monotonically with size. The combination of acoustic telemetry and stable isotope analysis revealed ontogenetic shifts in use of space and diet across short distances in a tropical coastal lagoon.

High interindividual variability in habitat selection and functional habitat relationships in European nightjars over a period of habitat change.

An animal's choice of foraging habitat reflects its response to environmental cues and is likely to vary among individuals in a population. Analyzing the magnitude of individual habitat selection can indicate how resilient populations may be to anthropogenic habitat change, where individually varying, broadly generalist populations have the potential to adjust their behavior. We collected GPS point data from 39 European nightjars (Caprimulgus europaeus) at a UK breeding site where restoration measures have altered large areas of habitat between breeding seasons. We calculated individual habitat selection over four breeding seasons to observe changes that might align with change in habitat. We also analyzed change in home range size in line with change in habitat availability, to examine functional relationships that can represent trade‐offs made by the birds related to performance of the habitat.Individual explained more of the variation in population habitat selection than year for most habitat types. Individuals differed in the magnitude of their selection for different habitat types, which created a generalist population composed of both generalist and specialist individuals. Selection also changed over time but only significantly for scrub habitat (60% decrease in selection over 4 years). Across the population, individual home range size was 2% smaller where availability of cleared habitat within the home range was greater, but size increased by 2% where the amount of open water was higher, indicating the presence of trade‐offs related to habitat availability. These results highlight that using individual resource selection and specialization measures, in conjunction with functional responses to change, can lead to better understanding of the needs of a population. Pooling specialist and generalist individuals for analysis could hide divergent responses to change and consequently obscure information that could be important in developing effective conservation strategies.

Home range of raccoon dogs in an urban green area of Tokyo, Japan

The raccoon dog (Nyctereutes procyonoides viverrinus) has recently become common in urban environments in Japan. We predicted that, like other carnivores adapted to urban environments, raccoon dogs in urban areas should have smaller home ranges than those in rural areas. We investigated the size of home ranges of raccoon dogs in the Akasaka Imperial Grounds, a 51-ha green area in central Tokyo. Between August 2012 and August 2014, 7 adult males and 4 adult females were radiotracked. Mean (± SD) home range size of these 11 raccoon dogs (100% minimum convex polygon = 17.6 ± 13.0 ha; 95% fixed kernel = 8.3 ± 5.7 ha) was smaller than that of raccoon dogs in rural areas obtained in previous studies, and core areas (75% local convex hull) averaged 3.7 ± 4.1 (SD) ha. We detected no seasonal changes in home range size. These results were consistent with the notion that urban carnivores typically have small home ranges. The small home range size seems to be explained by abundance of food resources, restricted environment, and the high population density of raccoon dogs in the urban green area.

Movements of dingoes on K’gari-Fraser Island: implications for management

ABSTRACTDingoes (Canis lupus dingo) on K’gari-Fraser Island have interacted with humans in unacceptable ways, with regular attacks and even a death of a child. Public interest in maintaining a viable dingo population on the island is intense. Hence, there is an imperative to improve the management of dingo–human interactions, and knowledge of dingo movement behaviour can assist in this effort. Eighteen dingoes (10 female, 8 male) were captured in 2011 and fitted with GPS collars programmed to record a location every two hours. Dingoes were monitored for an average of slightly more than 205 days. Total home range sizes ranged from 547 to 57,459 ha. (95 per cent fixed kernel estimate). Home ranges were also calculated for each animal during different phases of the breeding cycle. We identified four general types of movement: beach dwellers, predominantly coast and beach dwellers, coast to coast movers and mostly inland dwellers. There are some animals that have minimal chance of ever interacting with humans. There was a seasonal change in home range size with dingoes of both sexes moving further when they did not have dependent young. The home ranges we measured were comparable with mainland dingoes, offering no evidence that prey is scarcer than on the mainland.

How residents behave: home range flexibility and dominance over migrants in a Mediterranean passerine

Residency has repeatedly evolved in many migratory animals, some of which have preserved the anatomical adaptations to perform long-range movements. This is the case for partially migratory populations of Mediterranean passerines in which migrants and residents both have a migrant morphology. The question of how selection maintains residency in this situation remains unclear. Using radiotelemetry, we followed the resident fraction of a partially migratory population of blackcaps, Sylvia atricapilla, from eastern Spain and studied changes in home range size and habitat composition throughout three breeding and two wintering seasons. We then compared these birds with two groups of migratory blackcaps present in the area: in winter with migrants that breed in northern populations and in spring with migrants that breed locally. In addition, we observed aggressive interactions between individually marked birds to explore dominance relationships during winter. The home ranges of resident blackcaps were six times larger in winter than during the breeding season, but within each season, they were comparable in size to those of migrants. The habitats used by residents markedly differed between seasons as well as from those of migrants in winter, but not during the breeding season. In winter, resident birds were dominant over migrants, although migrants were generally larger. Overall, residents showed high between-season flexibility in home range size and habitat use. Winter home ranges of residents included breeding sites and more diverse types of habitats than those of northern migrants. This suggests that in winter, the importance of dominance for obtaining priority access to food may be high but not crucial, given that residents may reduce competition by feeding separately from migrants. Future studies should focus on whether residents show specific personalities and on the role of yearly oscillations in environmental conditions in maintaining residency in this type of partially migratory population.

Effects of surgical and chemical sterilization on the behavior of free-roaming male dogs in Puerto Natales, Chile

Population management of free-roaming domestic dogs (Canis lupus familiaris) is of interest due to the threat these animals pose to people, other animals and the environment. Current sterilization procedures for male dogs include surgical and chemical methods. However, little is known about how these procedures affect their behavior. The primary objective of this study was to investigate changes in selected behaviors following chemical and surgical sterilization in a male free-roaming dog (FRD) population in southern Chile. We also examined the association between serum testosterone levels and behaviors thought to be influenced by circulating androgens. A total of 174 dogs were randomly assigned to either a surgical or chemical sterilization group, or a control group. At the onset of the intervention period, 119 dogs remained and 102 dogs successfully completed the study. Each dog was monitored pre- and post-intervention using video recordings, GPS collars, and blood samples for the measurement of testosterone. Analysis of behavior revealed that surgically castrated dogs showed no reduction of sexual activity or aggression when compared to their pre-intervention behavior. Chemically sterilized dogs showed a statistically significant increase in dog-directed aggression, but no change in sexual activity. There was no change in home range size in any groups between the pre- and post-intervention measurement. We found no consistent association between levels of serum testosterone concentration and behavioral changes in any of the groups. This study presents the first detailed behavioral observations following surgical and chemical sterilization in male FRDs. The information generated is highly relevant to communities struggling with the control of FRDs. Complementary studies to further our understanding of the effects of male sterilization on the behavioral and reproductive dynamics of FRD populations are needed.

Erratum to: Does estimator choice influence our ability to detect changes in home-range size?

© 2015 Signer et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Erratum to: Animal Biotelemetry (2015) 3:16 DOI 10.1186/s40317‐015‐0051‐x The original version of this article unfortunately contains mistakes. The last two paragraphs in Background were moved to make the Conclusion and this is not correct. Please find below the correct text for each section. The correct Background is below:

Does estimator choice influence our ability to detect changes in home-range size?

Estimates of home-range size are frequently used to compare areal requirements of animals over time or space. Comparative studies of home-range estimators have highlighted extreme differences among general classes of methods (e.g., polygon-based and kernel density-based estimators) and sensitivity to the choice of various tuning parameters (e.g., amount of smoothing). These studies, however, have largely failed to consider how estimates of home-range size are typically used in applied research. We illustrate simulation-based methods for comparing estimators, which focus on relative differences in home-range size (over time or space), rather than their absolute magnitude. We also consider Global Positioning Technology (GPS) location data from a black bear (Ursus americanus) from northwestern Minnesota, USA, to illustrate the relevance to real-world data applications. In our examples, estimates of home-range size often differed considerably in absolute magnitude. Yet, for relative differences, the choice of home-range estimator was often negligible. Furthermore, choosing the right estimator was less important than other aspects of study design (e.g., number of animals followed). Many questions in ecology focus on changes in space-use patterns (over space or time). For these types of questions, home-range estimators should be evaluated in terms of their ability to detect these spatial and temporal patterns. More importantly, home-range estimation should be seen as a means to an end—i.e., estimators provide indices useful for addressing interesting biological questions or hypotheses—rather than as an end to itself.

Home-range size and habitat selection by male Island Foxes (Urocyon littoralis) in a Low-Density Population

Island foxes (Urocyon littoralis) are listed as federally endangered on four of the six California Channel Islands to which they are endemic. The population on Santa Rosa Island declined by 99% during the 1990s due to golden eagle (Aguila chrysaetos) predation but is now recovering. This drastic population reduction provided an unprecedented opportunity to study home-range size and habitat use at very low levels of intraspecific competition. We used global positioning system (GPS) collars to track 14 adult male foxes from September 2009 through June 2010. On average, the collars operated for 16.5 wk, yielding 364 locations per fox. The 95% minimum convex polygon home ranges averaged 3.39 km2, which is several times larger than reported in previous studies conducted at higher population densities. We used Euclidean distance analysis to assess habitat selection within 95% kernel density isopleth (KDI) home ranges and 50% KDI core areas. The foxes used most of the available vegetation types but exhibited significant selection for valley bottoms and for bare areas and grassland at night. Our results, together with previous studies on island foxes, suggest an inverse relationship between home-range size and population density as has been shown for many other species. However, the pattern is confounded by differences among study areas and methods. We therefore recommend that this study be repeated when the Santa Rosa Island population recovers to its historic density of 4 adult foxes/km2 to better assess density-dependent changes in home-range size and habitat use.

Interactions between density, home range behaviors, and contact rates in the Channel Island fox (Urocyon littoralis).

Many of the mechanisms underlying density-dependent regulation of populations, including contest competition and disease spread, depend on contact among neighboring animals. Understanding how variation in population density influences the frequency of contact among neighboring animals is therefore an important aspect to understanding the mechanisms underlying, and ecological consequences of, density-dependent regulation. However, contact rates are difficult to measure in the field and may be influenced by density through multiple pathways. This study explored how local density affects contact rates among Channel Island foxes (Urocyon littoralis) through two pathways: changes in home range size and changes in home range overlap. We tracked 40 radio-collared foxes at four sites on San Clemente Island, California. Fox densities at the four sites ranged from 2.8 ± 1.28 to 42.8 ± 9.43 foxes/km2. Higher fox densities were correlated with smaller home ranges (R2 = 0.526, F1,38 = 42.19, P < 0.001). Thirty foxes wore collars that also contained proximity loggers, which recorded the time and duration of occasions when collared foxes were within 5 m of one another. Contact rates between neighboring fox dyads were positively correlated with home range overlap (R2 = 0.341, P = 0.008), but not fox density (R2 = 0.012, P = 0.976). Individuals at high densities had more collared neighbors with overlapping home ranges (R2 = 0.123, P = 0.026) but not an increase in the amount of contact between individual neighbors. This study was the first time contact rates were directly measured and compared to density and home range overlap. Results suggest that foxes exhibit a threshold in their degree of tolerance for neighbors, overlap is a reliable index of the amount of direct contact between island foxes, and disease transmission rates will likely scale with fox density.

Changes in home range sizes and population densities of carnivore species along the natural to urban habitat gradient

AbstractWith rapid development and the spread of urbanized land, there is an increasing need to understand species' responses to urban conditions. Carnivores are considered to be sensitive to urbanization; however, there is ample evidence that some carnivore species successfully inhabit urban areas, and human‐modified habitats have recently been recognized as an important refuge for several species.Despite the increasing number of studies on urban carnivore ecology, no comprehensive cross‐species comparisons have been made in order to assess the effects of urbanization on the spatial ecology of carnivores and their population densities. Such a review could provide interesting insight into how some carnivore species respond to increasing urbanization. Specifically, we examine changes in population density and home range size of eight carnivore species that occur along the natural–urban environmental gradient.Using data from 411 articles, we provide evidence that the home range size of carnivores decreases in six out of eight species, and population density increases in three out of six species along the natural–urban habitat gradient. The density‐dependent pattern of variation in home range size is consistent in all species studied.Our results emphasize the remarkable ability of some carnivore species to adapt to novel environments through their behavioural flexibility and life history adaptations. We outline ideas for future research that could be adopted in addressing this phenomenon, namely comparative approaches and detailed studies of biotic and abiotic conditions along natural–urban gradients.

Whitebark Pine, Population Density, and Home-Range Size of Grizzly Bears in the Greater Yellowstone Ecosystem

Changes in life history traits of species can be an important indicator of potential factors influencing populations. For grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE), recent decline of whitebark pine (WBP; Pinus albicaulis), an important fall food resource, has been paired with a slowing of population growth following two decades of robust population increase. These observations have raised questions whether resource decline or density-dependent processes may be associated with changes in population growth. Distinguishing these effects based on changes in demographic rates can be difficult. However, unlike the parallel demographic responses expected from both decreasing food availability and increasing population density, we hypothesized opposing behavioral responses of grizzly bears with regard to changes in home-range size. We used the dynamic changes in food resources and population density of grizzly bears as a natural experiment to examine hypotheses regarding these potentially competing influences on grizzly bear home-range size. We found that home-range size did not increase during the period of whitebark pine decline and was not related to proportion of whitebark pine in home ranges. However, female home-range size was negatively associated with an index of population density. Our data indicate that home-range size of grizzly bears in the GYE is not associated with availability of WBP, and, for female grizzly bears, increasing population density may constrain home-range size.

Effects of clear-fell harvest on bat home range.

We investigated effects of roost loss due to clear-fell harvest on bat home range. The study took place in plantation forest, inhabited by the New Zealand long-tailed bat (Chalinolobus tuberculatus), in which trees are harvested between the ages 26–32 years. We determined home ranges by radiotracking different bats in areas that had and had not been recently clear-fell harvested. Home ranges were smaller in areas that had been harvested. Adult male bats selected 20–25 year old stands within home ranges before and after harvest. Males selected edges with open unplanted areas when harvest had not occurred but no longer selected these at proportions greater than their availability post harvest, probably because they were then readily available. This is the first radiotracking study to demonstrate a change in home range size and selection concomitant with felling of large areas of plantation forest, and thus quantify negative effects of forestry operations on this speciose group. The use of smaller home ranges post-harvest may reflect smaller colony sizes and lower roost availability, both of which may increase isolation of colonies and vulnerability to local extinction.

Movement patterns of an arboreal marsupial at the edge of its range: a case study of the koala.

BackgroundConservation strategies derived from research carried out in one part of the range of a widely distributed species and then uniformly applied over multiple regions risk being ineffective due to regional variations in species-habitat relationships. This is particularly true at the edge of the range where information on animal movements and resource selection is often limited. Here, we investigate home range size, movement patterns and resource selection of koalas Phascolarctos cinereus in the semi-arid and arid landscapes of southwest Queensland, Australia. We placed collars with GPS units on 21 koalas in three biogeographic regions. Home range sizes, resource selection and movement patterns were examined across the three regions.ResultsHabitat selectivity was highest at the more arid, western edge of the koala’s range with their occupancy restricted to riparian/drainage line habitats, while the more easterly koalas displayed more variability in habitat use. There was no significant difference between home range sizes of koalas at the western edge of the range compared to the more easterly koalas. Instead, variability in home range size was attributed to spatial variations in habitat quality or the availability of a key resource, with a strong influence of rainfall and the presence of freestanding water on the home range size of koalas. Within a 580 m spatial range, movement patterns of male and female paths showed a tortuous trend, consistent with foraging behavior. Beyond this spatial range, male paths showed a trend to more linear patterns, representing a transition of movement behavior from foraging to breeding and dispersal.ConclusionsThe difference in home range movement patterns and resource use among the different koala populations shows that behavior changes with proximity to the arid edge of the koala’s range. Changes in home range size and resource use near the range edge highlight the importance of further range-edge studies for informing effective koala conservation and management actions, especially when developing species-specific adaptation responses to climate change.Electronic supplementary materialThe online version of this article (doi:10.1186/2051-3933-1-8) contains supplementary material, which is available to authorized users.

Ranging behavior of Mahale chimpanzees: a 16 year study

We have analyzed the ranging patterns of the Mimikire group (M group) of chimpanzees in the Mahale Mountains National Park, Tanzania. During 16years, the chimpanzees moved over a total area of 25.2 or 27.4km(2), as estimated by the grid-cell or minimum convex polygon (MCP) methods, respectively. Annually, the M group used an average of 18.4km(2), or approximately 70%, of the total home-range area. The chimpanzees had used 80% of their total home range after 5years and 95% after 11years. M group chimpanzees were observed more than half of the time in areas that composed only 15% of their total home range. Thus, they typically moved over limited areas, visiting other parts of their range only occasionally. On average, the chimpanzees used 7.6km(2) (in MCP) per month. Mean monthly range size was smallest at the end of the rainy season and largest at the end of the dry season, but there was much variability from year to year. The chimpanzees used many of the same areas every year when Saba comorensis fruits were abundant between August and January. In contrast, the chimpanzees used several different areas of their range in June. Here range overlap between years was relatively small. Over the 16years of the study we found that the M group reduced their use of the northern part of their range and increased their frequency of visits to the eastern mountainous side of their home range. Changes in home-range size correlated positively with the number of adult females but not with the number of adult males. This finding does not support a prediction of the male-defended territory model proposed for some East African chimpanzee unit-groups.