Habitat Usage Research Articles

Toward a Sustainable Fishery Management Policy

This article proposes an Artificial Neural Network (ANN) model to predict neonatal and juvenile bull shark habitat usage in the Sabine Pass, located within the Gulf of Mexico between Louisiana and Texas. Given continuing discussion regarding overfishing of all shark species, including bull sharks, in the northwestern Atlantic and Gulf of Mexico, the research objective was to analyze environmental data proven to be conducive to bull shark early life stages and to use these data in an ANN to predict bull shark presence during late spring and throughout summer months at designated sampling sites. The results of this analysis can both aid decision making in a fisheries context and inform the discussion on bull shark habitat usage in general, thereby contributing to the discussion of whether or not the need exists for conservation efforts to ensure sustainability of the species as part of an effective bull shark management plan.

Diurnal Activity Budget and Habitat Usage of Four Ciconiiformes Species at the Annaiwilundawa Ramsar Wetland Sanctuary, Sri Lanka

Annaiwilundawa Ramsar wetland provides suitable habitats for a large number of residentand migratory bird species. Ciconiiformes of the Annaiwilundawa Ramsar wetland forms adiscernible component and hence have been identified as a potential bio-indicator group.Present study recorded the diurnal activity budgets of four Ciconiiformes species, namelyPurple Heron (Ardea purpurea), Intermediate Egret (Ardeola grayii), Indian Pond Heron(Egretta garzetta) and Little Egret (Mesophoyx intermedia) at the Annaiwilundawa Ramsarwetland once a month from December 2011 to November 2012.The day was divided in to three time periods as morning (6.15-10.15 hrs), noon (10.15-2.15hrs) and evening (2.15-6.15 hrs). Activities of the birds were categorized as feeding,locomotion, resting, preening, alert and searching. The activity of the birds and the habitat inwhich the activity occurred was recorded using focal and scan sampling methods in each timeperiod. Each bird species was observed for 30 minutes in each time period and the location ofthe observed bird species was recorded on a 1:50,000 scale topographical map of theAnnaiwilundawa. The marked points were jointed to conclude the ‘Used Area’ of the relevantspecies.All four species had significant difference in the diurnal activity budgets in each time period.Resting was the most dominant behaviour of these four species {[PurpleHeron=57.83±18.54%], [Indian Pond Heron=35.42±2.63%], [Little Egret=34.11±3.16%] and[Intermediate Egret=40.12±12.56%]}. Size of the area used by the four Ciconiiformes speciesdid not differ significantly (ANOVA, F=2.064, P≥0.1110). However, they showed significantrelationships between percentage time spent in different habitats and there availability withinthe ‘Used Area’ (Spearman correlation, Purple Heron z = 3.258, P≤0.0011; Indian PondHeron z=3.087, P≤ 0.0020; Little Egret z=1.978, P≤0.0480; Intermediate Egret z=3.335,P≤0.0008). Present study indicated that these four species of Ciconiiformes used theAnnaiwilundawa reservoir primarily for resting. Clear habitat partition and area usage wasobserved which may have allowed these four species to co-exist sympatrically at theAnnaiwilundawa Ramsar wetland.

Accounting for habitat when considering climate: has the niche of the Adonis blue butterfly changed in the UK?

The dramatic recovery of three species of grassland specialist butterfly threatened with extinction at their high latitude range limits in the 1980s has been attributed to two factors: increased grazing on calcareous grassland sites and warmer air temperatures. Both result in the warming of soil surface temperatures, favourable to the larvae of these species. We address the influence of both of these factors on the habitat usage of the butterfly Polyommatus bellargus, undergoing recovery at its northern range edge. We test the hypothesis that the larval niche of P. bellargus has become less constrained in the past three decades, whilst controlling for changes in habitat structure. Once habitat change has been accounted for we find no evidence for a broadening of the larval niche of P. bellargus. Further, we show that coincident with the recovery of P. bellargus there have been drastic reductions in average turf height across UK chalk grasslands, but changes in air temperature have been highly variable. We conclude that changes to soil surface temperatures caused by reducing turf heights will have been a more consistent influence than air temperature increases, and so habitat improvements through increased grazing will have been the major driver of recovery in P. bellargus. We consider the need to account for changes in habitat when exploring the impacts of recent climate change on local habitats in thermophilous species, and emphasise the continued importance of habitat management to support such species under variable local climates.

The effect of targeted stocking on behaviour and space utilization of a released finfish

Abstract Targeted stocking involves the release of fish directly into high-quality habitat, however this is often time-consuming, expensive and difficult. Acoustically tagged hatchery-reared juvenile mulloway Argyrosomus japonicus were released in groups directly into deep-hole habitat preferred by wild conspecifics (targeted stocking), or in a non-targeted fashion near easily accessible sites that lacked high-quality habitats in the direct vicinity. Fish were tracked continuously, 24 h d−1, for 5 d following release. Fish released in a targeted fashion showed lower mean activity rates (50% less movement) and occupied higher quality habitats than fish released in a non-targeted fashion. Fish released in a non-targeted fashion also used a greater number of smaller habitat patches. The implications for improvements in behaviour and habitat usage patterns for fish released in a targeted fashion, such as improved growth and survival, are discussed. Identifying and releasing fish directly into the species' high-quality habitat may ultimately improve the success of stocking programs.

Habitat used by juvenile lake sturgeon (Acipenser fulvescens) in the North Channel of the St. Clair River (Michigan, USA)

Lake sturgeon (Acipenser fulvescens) occupy the St. Clair River, part of a channel connecting lakes Huron and Erie in the Laurentian Great Lakes. In the North Channel of the St. Clair River, juvenile lake sturgeon (3–7years old and 582–793mm in length) were studied to determine movement patterns and habitat usage. Fourteen juveniles were implanted with ultrasonic transmitters and tracked June–August of 2004, 2005 and 2006. Telemetry data, Geographic Information System software, side-scan sonar, video images of the river bottom, scuba diving, and benthic substrate samples were used to determine the extent and composition of habitats they occupied. Juvenile lake sturgeon habitat selection was strongly related to water depth. No fish were found in <6m of water and over 97% of the relocations were found at depths greater than 9m. Available water depths exceeding 18m only represented 3.5% of the available habitat, however 34.9% of the relocations were found at depths exceeding 18m. Juvenile lake sturgeon did not use most areas in proportion to their availability. Sturgeon avoided clay ledges and shallow areas with silt or soft clay, which comprised approximately 39% of the benthic habitat in the North Channel. A total of 300 out of 351 documented locations were on sand and gravel habitat types mixed with clay. Lake sturgeon >700mm in length selected sand and gravel areas mixed with zebra mussels and areas dominated by zebra mussels, while fish<700mm used these habitat types in proportion to their availability.

Health of white sucker within the St. Louis River area of concern associated with habitat usage as assessed using stable isotopes.

In Spring 2011, 200 adult white sucker were collected in four areas of the St. Louis River area of concern (AOC), located in Minnesota and Wisconsin, USA. The areas included the upper AOC as a reference area, the upper estuary, St. Louis Bay and Superior Bay. Grossly visible abnormalities were documented and preserved for microscopic analyses, as were five to eight representative pieces of liver tissue. A piece of dorsal muscle was preserved for stable isotope analyses and otoliths removed for age determination. The incidence of raised skin lesions (mucoid plaques) was high (31 %), however, microscopically only 4.5 % of the white suckers had neoplasia (papillomas). The remaining lesions were epidermal hyperplasia. Superior Bay had the lowest percentage of skin/lip lesions (10 %), while St. Louis Bay had the highest (44 %). St. Louis Bay also had the highest incidence of skin neoplasms (12 %). No hepatocellular neoplasms were documented, however bile duct tumors were observed in 4.5 % of the suckers. Foci of cellular alteration were observed in fish from all sites except the upper AOC. Stable isotope data indicated that most of the suckers relied on the St. Louis River AOC for the majority (>75 %) of their diet, indicating they were resident within the AOC and not in Lake Superior. The amount of diet obtained from the upper estuary was a significant predictor of skin lesion incidence. Hence, habitat use within the AOC appears to be an important risk factor for skin and possibly, liver lesions.

Effect of Food Supply on Foraging Patterns and Body Weights of Long-Toed Stints(Calidris Subminuta)

Multiple species of shorebirds are now globally threatened, particularly across tropical Asia, yet we know relatively little of the detailed habitat usage and resource characteristics of sites in the region. The objective of this study was to determine how seasonal variation in food density affected foraging patterns and body weights of Long-toed Stint (Calidris subminuta), a relatively common winter visitor. Research was conducted during the passage and overwintering seasons in wastewater treatment ponds and salt-pans on the Inner Gulf of Thailand. Predictions were that during periods of higher food density, shorebirds should be relatively more abundant and heavier, and have increased foraging attempts, reduced step rates and reduced chase rates. Furthermore, adults were expected to have higher weights than juveniles. Overall, shorebird abundance was significantly positively correlated with invertebrate abundance during the 2-year study period. Long-toed Stints had greater body mass following their arrival in July-September, compared with later periods during the winter. Although food density and Long-toed Stint step rate were not significantly correlated, the data were consistent with previous studies suggesting a negative relationship. Step rates in salt-pans were significantly higher than in the wastewater treatment ponds, probably reflecting lower food densities in the salt-pans. There was no clear relationship between food density and Long-toed Stint peck rate, perhaps reflecting the weak correlation between number of pecks and the number of successful foraging bouts as well as limited sample sizes for prey estimates. There was no significant relationship between food density and chase rates. There was no significant difference in median body mass between adults and juveniles/first-year birds, implying young birds learn to forage as efficiently as adults relatively rapidly. This study suggests that further work on invertebrate dynamics and shorebird diets in the region is needed in order to build more predictive models of shorebird site usage and population dynamics.

Movement Patterns and Size‐Class Influence Entrainment Susceptibility of Lake Sturgeon in a Small Hydroelectric Reservoir

AbstractHydroelectric development is considered a threat to the recovery of Lake Sturgeon Acipenser fulvescens populations, in part because of injury and mortality concerns caused by interaction with hydroelectric facilities. Lake Sturgeon resident in small impoundments may be particularly susceptible to entrainment, depending on movement and habitat usage patterns. Using acoustic telemetry, we monitored coarse‐scale movements of 99 juvenile, subadult and adult Lake Sturgeon captured throughout a 10‐km‐long hydroelectric reservoir. Overall, adults moved over larger ranges than did smaller size‐classes. However, all size‐classes utilized habitat immediately upstream of hydroelectric facilities, and during the 18‐month study period, 27% of subadults tagged in the lowermost section of the reservoir, and 8.7% of adults tagged throughout the reservoir were entrained. Movements of juveniles and subadults were generally restricted to extended sections (2–6 km) of contiguous deepwater habitat (&gt;15 m), and passage through the two shallow river narrows that subdivide the reservoir were rare. Over half of the tagged adults (52%) moved upstream or downstream through one or both river narrows, albeit infrequently. Initial residency influenced entrainment susceptibility for juveniles and subadults but not for adults. Results suggest that Lake Sturgeon resident in small impoundments are susceptible to entrainment. However, the presence of river narrows, which function as natural movement restrictors, may largely preclude susceptibility of juveniles and subadults resident in upstream sections.

Ecology and diversity of a lizard community in the semiarid region of Brazil

Composition, species diversity and resource usage in terms of space and time were evaluated for the lizard community of the Ecological Station of the Seridó (ESEC Seridó), Rio Grande do Norte. An observation area of 150 m × 150 m (2.25 ha) was delimited and surveyed monthly in alternate turns (morning, afternoon and night) for three consecutive days from April to October 2011, covering dry and rainy seasons. Fourteen species belonging to eight families were recorded, being Tropidurus semitaeniatus the most abundant. Seasonality influenced species richness and abundance. Regarding habitat usage, Lygodactylus klugei was the most generalist species, whilePhyllopezus periosus, P. pollicaris and T. semitaeniatus were specialists, showing affinity for rocky formations. About microhabitat usage, the most generalist species was T. hispidus and the most specialized wasL. klugei . Ten of the recorded species have diurnal habits and four are nocturnal. The space and time usage profiles of the dominant species corroborated data obtained in previous autoecological studies conducted in the same area and suggest a pattern of resource usage by these species in the ESEC Seridó.

Ecological periodic tables: in principle and practice

“Science is organized knowledge.” Immanuel Kant (1724–1804)Ecological periodic tables are an information organizing system with categorical habitat types as elements and predictably recurring (periodic) properties of a target biotic community, such as its relative species richness, abundance and biomass, as attributes. Ecological periodic tables are founded on the ecological tenet that habitats structure biotic communities and its corollary that habitats are templets for ecological strategies. They are a durable, open and flexible system that accommodates all operationally defined habitat types and biotic communities for which the periodicity of habitat usage patterns by a biotic community have been empirically substantiated. Discovering quantitative, periodic habitat usage patterns requires quantitative, representative, unbiased sampling of a biotic community across habitat types at ecologically relevant temporal and spatial scales. Like chemical periodic tables, the Linnaean system of classification and the Hertzsprung–Russell diagram in chemistry, biology and astronomy, respectively, ecological periodic tables are simple, easy to understand, exceptionally useful and they foster the expansion of scientific understanding, inquiry and theory.

Daily and seasonal movements of a shrubland-obligate breeder in relation to mature forest edge habitat

The effects of edge habitat on wildlife populations have been studied extensively in recent decades, but most studies have focused on describing patterns of edge effects rather than identifying the mechanisms driving these effects. Based on evidence of lower densities of shrubland birds in edge versus interior habitat, we tested four hypotheses that could produce a pattern of apparent edge avoidance: (1) active avoidance of edges due to high risk of predation in edge habitat, (2) conspecific interactions that promote greater use of interior habitat due to territorial defense, (3) passive displacement of avian home ranges, such that sampling in the interior is more likely to intersect multiple home ranges compared to sampling at edges, and (4) home range expansion along edges. To test these hypotheses, we radio-marked 39 male Yellow-breasted Chats (Icteria virens) during the breeding seasons of 2005 and 2006 and relocated each bird 4–5days/week. Our results did not support the hypothesis that Yellow-breasted Chats avoided habitat edges in either home range placement or habitat usage within their home ranges though there was some support for greater usage of interior habitat during the peak of the breeding season. Size of home ranges did not vary with distance from edge. These results support the passive displacement hypothesis and, to a lesser extent, the conspecific interactions hypothesis. The passive displacement hypothesis predicts lower abundances in the edges compared to the center of a habitat patch because areas in the patch center receive individuals from all directions whereas areas near the edges do not. Thus, edge habitat may still provide quality habitat for shrubland birds in our system.

Behavioral plasticity of a threatened parrot in human-modified landscapes

Behavioral plasticity is a strategy employed by many species to cope with both naturally occurring and human-mediated environmental variability. Such plasticity may be especially important for long-lived and wide-ranging species, such as parrots, that likely face great temporal and spatial variation within their long lifespans, and are often disproportionately affected by anthropogenic habitat change. We used radio-telemetry and roost counts to assess ranging patterns, habitat usage, and roosting behaviors of the Yellow-naped Amazon (Amazona auropalliata) at two sites in northern Costa Rica with different degrees of anthropogenic habitat alteration. We compared behaviors for residents at the two sites and for experimentally translocated individuals to test the hypothesis that this species would employ behavioral plasticity in response to habitat differences. We found that individuals in the region with dispersed vegetation recorded ranging movements and communal roosting behavior ten times larger than the region with concentrated vegetation. Translocated individuals showed flexibility in these behaviors and matched the behavioral patterns of resident birds at the release site rather than maintaining behaviors characteristic of their capture site. Our results illustrate a generalized rapid plastic response to human-induced changes in habitat for a number of behavioral traits in the Yellow-naped Amazon. Such plasticity is directly relevant to reintroduction efforts that are commonly employed as a conservation tool in parrots. Our study provides an example of how behavioral plasticity may allow some wild populations to withstand anthropogenic change.

Coevolution Trumps Pleiotropy: Carbon Assimilation Traits Are Independent of Metabolic Network Structure in Budding Yeast

Phenotypic traits may be gained and lost together because of pleiotropy, the involvement of common genes and networks, or because of simultaneous selection for multiple traits across environments (multiple-trait coevolution). However, the extent to which network pleiotropy versus environmental coevolution shapes shared responses has not been addressed. To test these alternatives, we took advantage of the fact that the genus Saccharomyces has variation in habitat usage and diversity in the carbon sources that a given strain can metabolize. We examined patterns of gain and loss in carbon utilization traits across 488 strains of Saccharomyces to investigate whether the structure of metabolic pathways or selection pressure from common environments may have caused carbon utilization traits to be gained and lost together. While most carbon sources were gained and lost independently of each other, we found four clusters that exhibit non-random patterns of gain and loss across strains. Contrary to the network pleiotropy hypothesis, we did not find that these patterns are explained by the structure of metabolic pathways or shared enzymes. Consistent with the hypothesis that common environments shape suites of phenotypes, we found that the environment a strain was isolated from partially predicts the carbon sources it can assimilate.

Effects of resource limitation on habitat usage by the browser guild in Hluhluwe-iMfolozi Park, South Africa

Abstract:Resource depletion and associated increases in interspecific competition are likely to influence differential habitat usage amongst a guild. We tested some prominent theoretical concepts using observed differences in seasonal habitat use amongst the savanna browser guild (elephant, giraffe, impala, kudu and nyala) in Hluhluwe-iMfolozi Park, South Africa. Herbivore locations (n = 3108) were recorded over 2 y using repeated road transects and, for elephant, GPS collars (187 254 downloads). Densities were calculated using a novel GIS approach designed to be a cost-effective method for annual censuses, but also able to cope with abrupt changes in visibility. Selectivity for (Manly's α) vegetation types, and overlap (Schoener's index) in vegetation type usage were calculated. Resource depletion in the dry season resulted in all members of the guild increasing selectivity for vegetation types (sum of absolute values away from the neutral value for Manly's alpha for the guild: dry seasons 3.97, 5.16; corresponding wet seasons 3.12, 3.68), but decreasing interspecific overlap (80% of Schoener's indices lower in dry season versus wet season). These effects were more marked over the second, more severe, dry season. We found support for the niche overlap hypothesis and the niche compression hypothesis. The Jarman–Bell principle was generally supported, although unexpectedly during the severe dry season elephant showed the most selectivity for vegetation type. The greater the resource depletion, the more relevant interspecific differences in habitat usage become in relation to the differential impacts of guild members.

First assessment of the endoparasitic nematode fauna of four psammophilous species of Tropiduridae (Squamata: Iguania) endemic to north-eastern Brazil

Tropiduridae (Squamata: Iguania) is a lizard taxon widely distributed in the neotropics. Among its representatives, some species are classified as generalists regarding habitat usage. Others exhibit a very restricted and probably relict distribu- tion, and are strongly associated with predominantly sandy and dry habitats. Within this rather ecologically similar than phylogenetically closely related group we examined specimens of Eurolophosaurus amathites , E. divaricatus, Tropidurus hygomi, T. psam- monastes for endoparasites. In all four species examined we recorded parasitic nema- todes (Nemathelminthes: Nematoda). At least three nematode species were recovered: Parapharyngodon sp., Physaloptera lutzi and Strongyluris oscari, with Ph. lutzi being the most abundant parasite encountered in all lizard species examined. In spite of the hosts' habitat specialization, these parasites are also found frequently in non-psammo - philous tropidurid species as well as in other squamates. Individual species richness per lizard was low, with usually just one species parasitizing at a time. These are the first parasites registered for these tropidurids and constitute a total of six new host records.

Population trends of common breeding and wintering birds in Hungary, decline of longdistance migrant and farmland birds during 1999–2012

Abstract Based on the Hungarian common bird monitoring scheme (MMM), which is the longest running country-wide monitoring using formal sampling design with representative data for the main habitats in Central-Eastern Europe, we investigated the population trends of common breeding and wintering species. Habitat preference and occupancy of the common breeders, migration strategies and relationships among these characteristics could act behind the population trends. We pointed out that long distance migrant bird species had strong decreasing trends in Hungary and very probably in the entire Pannonian biogeographical region, whereas the partial and short migrant species has increasing trends. Farmland birds had declining trend, which trend became more obvious since the joining of Hungary to the EU. The negative changes in the farmland habitat could influence bird species nesting/foraging mainly in this habitat independently from their migration strategies. Our investigations let us to develop indicators on the basis of migration strategy and habitat usage of common birds to provide regular information about condition of groups of species and their habitats in Hungary and the Pannonian region. The MMM database provide unique opportunity for further investigations of several species, habitats and area specific in a part of Europe where this kind of information is rare yet.

Reassessment of morphology and historical distribution as factors in conservation efforts for the Endangered Patagonian Huemul Deer Hippocamelus bisulcus (Molina 1782)

To assist with conservation of Endangered Patagonian Huemul Deer (Hippocamelus bisulcus), the Huemul Task Force (HTF) reassessed information on appendicular morphology, paleobiogeography, and historical distribution as potential factors in recovery efforts. Traditional claims of being a mountain specialist of the Andes were refuted by empirical evidence showing huemul morphology to coincide with other cervids rather than the commonly implied homology to rock-climbing ungulates. It thus supports historical evidence of huemul in treeless habitat and reaching the Atlantic coast, which cannot be dismissed as past erroneous observations. Instead, pre- and post-Columbian anthropogenic impacts resulted in huemul displacement from productive sites and in survival mainly in remote and marginal refuge areas. The process of range contraction was facilitated by easy hunting of huemul, energetic incentives from seasonal fat cycles and huemul concentrations, the change from hunting-gathering to a mobile equestrian economy, and colonization with livestock. However, areas used presently by huemul, as supposed mountain specialists, are also used by wild and domestic ungulates that clearly are not considered mountain specialists, whereas the only other Hippocamelus successfully uses areas homologous to tree-less Patagonia. Rigid application of modern habitat usage to infer past habitat use and ignoring historic extra-Andean accounts is unwarranted; these conclusions reached by the HTF indicate new opportunities for recovery efforts by considering morphological and historical evidence. For instance, reintroductions to other portions of the landscape used formerly by huemul, which tend to be more productive sites than those currently occupied by many huemul groups, would present a promising avenue.

Comparison of abundance and habitat usage for common bottlenose dolphins between sites exposed to differential anthropogenic stressors within the estuaries of southern Georgia, U.S.A

AbstractThe health of common bottlenose dolphins (Tursiops truncatus) within southern Georgia estuaries is of particular concern due to high levels of anthropogenic contaminants in their tissues. Dolphins in this region have the highest polychlorinated biphenyl (PCB) concentrations recorded for any marine mammal and these concentrations correlate to distance from a Superfund point‐source in the Turtle/Brunswick River Estuary (TBRE). Currently, little is known about the population structure of dolphins in this region. This study identifies and compares baseline data on abundance, habitat use, site‐fidelity, and ranging patterns of dolphins across two adjacent field sites; Brunswick, including the TBRE, and Sapelo, including the Sapelo Island National Estuarine Research Reserve. Sapelo is relatively undeveloped and was selected for comparison to the more contaminated TBRE. Dolphin densities increased with tributary size in both sites but dolphin density and total abundance were significantly higher in Sapelo than in Brunswick. Anthropogenic stressors within the TBRE may be an important factor contributing to the differences in abundance, density, and habitat use observed in this study.

Utilization of Sugarcane Habitat by Feral Pig (Sus scrofa) in Northern Tropical Queensland: Evidence from the Stable Isotope Composition of Hair

Feral pigs (Sus scrofa) are an invasive species that disrupt ecosystem functioning throughout their introduced range. In tropical environments, feral pigs are associated with predation and displacement of endangered species, modification of habitat, and act as a vector for the spread of exotic vegetation and disease. Across many parts of their introduced range, the diet of feral pigs is poorly known. Although the remote location and difficult terrain of far north Queensland makes observing feral pig behavior difficult, feral pigs are perceived to seek refuge in World Heritage tropical rainforests and seasonally ‘crop raid’ into lowland sugarcane crops. Thus, identifying how feral pigs are using different components of the landscape is important to the design of management strategies. We used the stable isotope composition of captured feral pigs to determine the extent of rainforest and sugarcane habitat usage. Recently grown hair (basal hair) from feral pigs captured in remote rainforest indicated pigs met their dietary needs solely within this habitat. Stable carbon and nitrogen isotope values of basal hair from feral pigs captured near sugarcane plantations were more variable, with some individuals estimated to consume over 85% of their diet within a sugarcane habitat, while a few consumed as much as 90% of their diet from adjacent forested environments. We estimated whether feral pigs switch habitats by sequentially sampling δ 13C and δ 15N values of long tail hair from a subset of seven captured animals, and demonstrate that four of these individuals moved between habitats. Our results indicate that feral pigs utilize both sugarcane and forest habitats, and can switch between these resources.

Two social communities in the Pearl River Estuary population of Indo-Pacific humpback dolphins (Sousa chinensis)

The way human activities impact animal populations can depend on social structure, which is important to understand in social species such as cetaceans. We investigated association patterns in Indo-Pacific humpback dolphins ( Sousa chinensis (Osbeck, 1765)) inhabiting the Pearl River Estuary near Lantau Island, Hong Kong, using a 10-year data set for 88 individuals. Our analyses revealed two social communities. Each had its own region of core use, to the north and to the west of the island, but their overall ranges partially overlapped northwest of Lantau. The northern community had a fission–fusion structure characterized by short-term associations, while the western community had more long-term associations. Mixed-community groups included calves more often than exclusive groups, so between-community associations may arise from common habitat usage, by females especially, in the overlap area. Recent range extensions by the northern community into the west are likely a response to habitat destruction north of Lantau. This suggests ease of movement between the north and the west is necessary for northern-community dolphins to access suitable habitat, and gives new concern to construction projects planned for the region. We emphasize our study as an example of how sociobiological information can be important in understanding human impacts on animal populations.