The morning sun breaks over the Annapurna massif, casting golden light across ridges that plunge from ice-clad summits to subtropical river valleys below. A shadow flickers across the snow: broad wings riding thermal currents with scarcely a wingbeat. This is the domain of the Accipitridae, the most diverse and ecologically dominant family of diurnal raptors on Earth. From the bone-crushing Himalayan Griffon soaring at 7,000 meters to the forest-dwelling Crested Goshawk weaving through rhododendron thickets, these birds have mastered every ecological niche the Himalayan realm offers.
Nepal, compressed between the Gangetic plains and the roof of the world, hosts over 60 species from this remarkable family. This concentration of diversity reflects both the region's extraordinary altitudinal range and its position along one of the planet's great migratory flyways. Understanding Accipitridae requires examining not just individual species, but the evolutionary forces, biomechanical innovations, and ecological strategies that have allowed this lineage to dominate the skies for millions of years.
Ancient Lineages: The Evolutionary Forge
The story of Accipitridae begins in the Oligocene and Miocene epochs, roughly 23 to 5 million years ago, when the first recognizable members of this lineage emerged across the supercontinent landscapes. Molecular phylogenetics conducted through 2026 has revolutionized our understanding of raptor evolution, revealing that the superficial similarities between hawks, eagles, and vultures mask an ancient and complex radiation that diverged from other raptor lineages far earlier than morphology alone suggested.
The critical distinction lies in understanding what Accipitridae are not. Unlike the Falconidae (falcons and caracaras), which recent genomic studies confirm belong to an entirely separate evolutionary branch closer to parrots and passerines, the Accipitridae represent a true raptor lineage within the Accipitriformes. They diverged from the Pandionidae (the single species osprey family) approximately 20 million years ago, developing along a trajectory that favored versatility over specialization. Where ospreys became supreme fish-catchers with reversible outer toes and spiny foot pads, Accipitridae evolved into generalists capable of exploiting every hunting strategy from active pursuit to patient scavenging.
The 2024 Catanach et al. molecular phylogeny represented a watershed moment in raptor systematics, fundamentally reorganizing genera that had remained stable since the 19th century. Their work, built on whole-genome sequencing across representative species, dismantled the traditional concept of Accipiter as a monolithic genus. Species previously lumped under this umbrella have now been redistributed across multiple lineages, with the resurrection of Astur and the recognition of several distinct evolutionary radiations within what ornithologists once considered a single group. This reclassification reflects the family's extraordinary age and the multiple independent evolutions of similar hunting strategies, a phenomenon that makes morphology alone an unreliable guide to relatedness.
By 2026, the family structure has crystallized into approximately 12 recognized subfamilies, including the well-known Aquilinae (true eagles), Accipitrinae (goshawks and sparrowhawks), Aegypiinae (Old World vultures), Circinae (harriers), Milvinae (kites), and the less familiar but equally significant Gypaetinae (bearded vultures) and Perninae (honey buzzards). Each subfamily represents millions of years of independent evolution, adapting to distinct ecological roles while retaining the core anatomical toolkit that defines the family: powerful talons, hooked beaks, and extraordinary visual acuity.
Architects of the Air: Form Follows Function
Walking through the collections of Nepal's Natural History Museum in Kathmandu, one is immediately struck by the morphological diversity within Accipitridae. A Lammergeier skull sits beside that of a Shikra, and the contrast seems almost impossible to reconcile within a single family. Yet the variations speak to the remarkable plasticity of the Accipitridae bauplan, a fundamental body architecture that has been sculpted by natural selection into forms optimized for radically different lifestyles.
The hooked bill, perhaps the most recognizable feature of the family, is far more than a simple killing tool. In vultures like the Himalayan Griffon, the bill has become a specialized butchering implement, capable of tearing through thick hide and accessing nutrient-rich organs that other scavengers cannot reach. The cutting edges of the maxilla work like surgical shears, while the powerful neck musculature (far more developed than in predatory members of the family) provides the force needed to dismember large carcasses. By contrast, the bills of forest hawks such as the Besra reflect a different imperative: speed and precision rather than raw power. Their shorter, more delicately curved beaks deliver quick, decisive strikes to small, agile prey, often targeting the cervical vertebrae for an instant kill.
The phenomenon of reversed sexual size dimorphism, where females significantly outweigh males, reaches its extreme expression in Accipitridae. Among sparrowhawks and goshawks, females can be up to 50 percent heavier than their male counterparts, a size differential that has puzzled ornithologists for generations. The prevailing hypothesis links this dimorphism to hunting efficiency and reproductive division of labor. Larger females can take bigger prey and defend nests more effectively, while smaller, more agile males specialize in capturing swift, evasive birds. This size split effectively allows a breeding pair to exploit a broader prey spectrum than either sex could alone, reducing competition between mates and increasing overall reproductive success.
Wing morphology within the family reveals evolution's response to the fundamental tradeoff between soaring efficiency and maneuverability. Vultures and large eagles have evolved broad, heavily slotted wings with pronounced primary feather separation, creating multiple small wing-tip vortices that reduce induced drag during soaring. The Himalayan Griffon's wingspan, reaching nearly three meters, demonstrates this adaptation at its most extreme. These birds can remain aloft for hours with minimal energy expenditure, riding mountain updrafts and thermals while scanning vast territories for carrion. Their wing loading (body weight relative to wing area) is among the lowest in the family, allowing them to utilize even weak thermal currents that would be insufficient for smaller, heavier-winged species.
Forest specialists have taken the opposite evolutionary path. The Crested Goshawk, hunting through dense Himalayan oak and rhododendron forests, possesses short, rounded wings and a long, flexible tail that functions as an aerial rudder. This configuration sacrifices soaring efficiency for explosive acceleration and tight-radius turns, allowing the bird to navigate through tangled branches in pursuit of prey. The biomechanical demands of forest hunting have independently produced similar wing shapes across multiple Accipitridae subfamilies, a textbook example of convergent evolution shaping form to match function.
The visual system of Accipitridae represents perhaps their most extraordinary adaptation. Raptor eyes contain a far higher density of photoreceptor cells than mammalian eyes, particularly in the foveal region responsible for high-acuity vision. Many species possess two foveas per eye (one for forward vision, one for lateral scanning), effectively giving them multiple points of maximum resolution. The Steppe Eagle, arriving in Nepal's lowlands each winter, can detect prey movements at distances exceeding two kilometers, resolving details that would appear as indistinct blurs to human observers. This visual supremacy, combined with superior color perception extending into the ultraviolet spectrum, allows Accipitridae to detect the urine trails of small mammals (which reflect UV light) and assess the health and maturity of potential prey from extraordinary distances.
Himalayan Corridor: Where Altitude Shapes Diversity
Nepal's geography reads like a natural experiment in altitudinal zonation. From the steaming Terai forests at 60 meters above sea level to the wind-scoured summits of the Himalaya reaching 8,848 meters at Sagarmatha (Mount Everest), the country compresses nearly the entire range of Asian ecosystems into a north-south gradient less than 200 kilometers wide. This extreme topographic complexity has made Nepal a global hotspot for Accipitridae diversity, with species adapted to every elevational band coexisting within a remarkably compact geographic area.
The lowland Terai and Siwalik hills support a distinct assemblage dominated by forest specialists and wetland hunters. Here, the Brahminy Kite patrols river margins and paddy fields, its striking russet and white plumage a common sight along the Koshi and Narayani river systems. The species exemplifies the opportunistic feeding strategies common in the Milvinae subfamily, equally comfortable snatching fish from water surfaces, scavenging carrion, or pirating prey from other birds. Further upslope, the Mahabharat range and middle mountains between 1,000 and 3,000 meters represent the richest zone for breeding raptors, where subtropical and temperate forests provide abundant prey and nesting habitat.
The high Himalaya, despite its harsh conditions, supports a specialized suite of Accipitridae adapted to life at the limits of avian physiology. The Lammergeier, or Bearded Vulture, has mastered the art of extracting nutrients from sources other scavengers ignore. This extraordinary species feeds primarily on bone marrow, carrying large bones to great heights and dropping them onto rock platforms (known locally as ossuaries) to shatter them and expose the calorie-rich interior. Recent studies tracking Lammergeiers in the Annapurna region have recorded individuals foraging at altitudes exceeding 7,500 meters, making them among the highest-flying birds on Earth. Their ability to thrive in these rarefied environments reflects specialized hemoglobin with enhanced oxygen-binding properties and exceptional thermal regulation.
Nepal's position along the Central Asian Flyway transforms the country into a migratory bottleneck of global significance. Each autumn, tens of thousands of raptors funnel through mountain passes and river valleys, following ancient routes between their breeding grounds in Central Asia and wintering areas across the Indian subcontinent. The Kali Gandaki valley, carved between the Annapurna and Dhaulagiri massifs as the world's deepest gorge, serves as a primary corridor for this migration. Here, in a single day during peak passage in October, observers have recorded over 10,000 individual raptors representing more than 20 species, a spectacle that ranks among the great avian migrations of the planet.
The Steppe Eagle exemplifies the migratory patterns that bring northern breeding populations into seasonal contact with resident Himalayan species. These powerful members of the Aquilinae subfamily breed across the steppes and semi-deserts from Kazakhstan to Mongolia, then undertake journeys of several thousand kilometers to winter in the relatively benign climate of the Gangetic plains and Himalayan foothills. Satellite tracking studies completed in 2025 revealed that individual Steppe Eagles show remarkable fidelity to specific wintering sites in Nepal, returning to the same river valleys and agricultural landscapes year after year. Their arrival in November coincides with the post-monsoon abundance of rodents and birds in lowland agricultural areas, demonstrating the tight coupling between migration phenology and prey availability.
The altitudinal gradients of Nepal create not just horizontal diversity but vertical migration patterns that rival the north-south movements of transboundary species. Many raptors breeding in high-altitude environments descend to lower elevations during winter, tracking the seasonal movement of prey populations. The Black Eagle, though not truly migratory, exhibits altitudinal movements that see individuals nesting at 3,000 meters in summer, descending to below 1,000 meters during harsh winter months. These elevational migrations, often overlooked compared to their latitudinal counterparts, represent critical adaptations to the extreme seasonality of mountain environments.
Predators and Scavengers: The Ecological Architectures of Hunting
Within the Accipitridae, hunting strategies span the full spectrum from active pursuit to obligate scavenging, with most species occupying positions along this continuum rather than at its extremes. These foraging modes reflect fundamental tradeoffs between energy expenditure and success rates, shaped by millions of years of natural selection optimizing each species for its ecological niche.
The sit-and-wait strategy, technically termed perch hunting, dominates among forest-dwelling Accipitridae. Species like the Crested Goshawk and Besra spend long periods motionless on concealed perches, their cryptic plumage rendering them nearly invisible against bark and foliage. This patient approach minimizes energy expenditure while maximizing the element of surprise. When prey appears within striking range, the attack unfolds with explosive speed, the bird accelerating from stillness to over 60 kilometers per hour in seconds. The success of this strategy depends critically on microhabitat selection: perches must offer clear sight lines to productive hunting areas while providing sufficient cover to avoid detection by wary prey.
Active soaring represents the opposite end of the energetic spectrum, trading immediate responsiveness for the ability to survey vast territories. Large eagles and vultures employ this strategy to maximum effect, using thermal currents and/or orographic updrafts to gain altitude with minimal wing-flapping. Once aloft, they can glide for kilometers, their exceptional eyesight scanning the landscape below for carrion or live prey. The Himalayan Griffon, with its enormous wingspan and low wing loading, can cover hundreds of square kilometers in a day's foraging, locating scattered carcasses that would be impossible to find through ground-based searching. Recent GPS tracking studies in Nepal have revealed that individual vultures maintain mental maps of their territories, returning repeatedly to productive sites and monitoring the movements of livestock herds whose members may soon provide foraging opportunities.
Between these extremes lies a diverse array of intermediate strategies. Harriers practice a distinctive low-quartering flight, coursing back and forth over grasslands and marshes at heights of just a few meters, dropping suddenly onto rodents and ground-nesting birds. The Montagu's Harrier, a passage migrant through Nepal, demonstrates this technique beautifully as it hunts across the Terai grasslands, its buoyant flight and facial disc (unusual in Accipitridae and evolved independently from owls) helping it locate prey by sound as well as sight.
Kleptoparasitism, the theft of prey from other hunters, appears sporadically across the family but reaches its zenith in certain species that have made it a primary foraging mode. The Greater Spotted Eagle, observed along Nepal's wetlands during migration, regularly harasses other raptors and waterbirds, forcing them to drop captured prey. This behavior represents an evolutionary gamble: the energetic savings of not hunting can be offset by the low success rate of piracy attempts and the risk of injury during aerial confrontations.
The transition to obligate scavenging represents one of the most dramatic ecological shifts within Accipitridae. Vultures have relinquished predation almost entirely, instead specializing in locating and consuming carrion. This lifestyle has driven profound morphological changes: the reduction of talon strength (since they no longer need to kill), the development of bare heads and necks (facilitating feeding deep inside carcasses without fouling plumage), and the evolution of digestive systems capable of neutralizing the toxins and pathogens abundant in decaying flesh. The White-rumped Vulture, once Nepal's most abundant scavenger, possesses stomach acid with a pH approaching 1.0, among the most corrosive biological fluids known, allowing it to digest bones, hide, and putrefied tissue that would be lethal to most other animals.
The social dynamics of scavenging have also shaped vulture behavior in ways unlike other Accipitridae. Carrion represents a patchy, unpredictable resource that appears sporadically but in quantities far exceeding any individual's needs. This has favored the evolution of information sharing through communal roosting and follow-the-leader behavior. When one vulture locates a carcass and descends, its conspicuous descent acts as a signal visible to others across vast distances, creating a cascade effect that can draw hundreds of birds to a single feeding site within hours. This social facilitation allows vultures to exploit resources more efficiently than solitary scavengers could, but also makes them vulnerable to poisoning events when contaminated carcasses attract entire regional populations.
Conservation in the Anthropocene: Triumphs and Ongoing Challenges
The vulture crisis that began in the 1990s represented one of the most precipitous wildlife collapses in recorded history. Across South Asia, populations of three Gyps species (the White-rumped, Indian, and Slender-billed Vultures) declined by over 99 percent in less than two decades, a catastrophe driven almost entirely by a single veterinary drug: diclofenac. This non-steroidal anti-inflammatory medication, administered to livestock, proved acutely toxic to vultures feeding on treated carcasses, causing kidney failure and death within days of exposure. By 2005, species that had numbered in the tens of millions had been reduced to scattered remnant populations, and extinction seemed inevitable.
Nepal's response to this crisis has established the country as a global leader in vulture conservation. Beginning in 2006, the government initiated a multi-pronged strategy combining captive breeding, habitat protection, and most critically, the phased elimination of diclofenac from veterinary use. By 2026, over 95 percent of Nepal's territory will have been declared a Diclofenac-Free Zone, with alternative drugs like meloxicam (proven safe for vultures) replacing the toxic medication across most of the country. This achievement required coordinating efforts across government ministries, veterinary associations, pharmaceutical companies, and local communities, demonstrating that effective conservation must address the socioeconomic realities that drive environmental threats.
The establishment of "Vulture Restaurants" (supplementary feeding sites providing safe carcasses) has played a crucial role in supporting remnant populations while diclofenac is phased out. These sites, now numbering over 20 across Nepal, provide regular meals of livestock carcasses certified free from toxic drugs. Monitoring at these restaurants has documented gradual population increases in White-rumped and Slender-billed Vultures, though numbers remain far below historical levels. The restaurants also serve as focal points for community education and ecotourism, helping local populations recognize vultures' ecological value and economic potential.
Yet despite these conservation successes, Accipitridae face an evolving array of threats in the Anthropocene. Climate change is already altering the Himalayan environment in ways that will profoundly impact raptor populations. Rising temperatures are pushing vegetation zones upslope, compressing the alpine and subalpine habitats where specialist species like the Lammergeier hunt. Glacial retreat is modifying hydrological patterns, affecting prey populations in ways still poorly understood. More immediately, extreme weather events appear to be increasing in frequency, with late spring snowstorms potentially devastating breeding success for high-altitude species.
Habitat fragmentation represents a pervasive threat, particularly in the middle elevations where human population density is highest. The conversion of forests to agricultural land and settlements reduces available nesting habitat and prey populations. Forest specialists like the Mountain Hawk-Eagle require large, contiguous tracts of mature forest for successful breeding, resources increasingly scarce in Nepal's intensively settled middle mountains. Road construction, accelerating rapidly across the country, fragments habitats while also creating new mortality sources through vehicle collisions.
Infrastructure development poses direct threats beyond habitat loss. Power transmission lines, essential for bringing electricity to remote communities, kill raptors through electrocution and collision. Large soaring species are particularly vulnerable, as their flight characteristics make it difficult to detect and avoid cables until too late. A 2025 study along major transmission corridors in western Nepal documented mortality rates approaching 10 birds per kilometer of line annually, suggesting that electrocution may now rival poisoning as a leading cause of non-natural mortality. Wind energy development, while environmentally beneficial in many respects, creates additional collision hazards. As Nepal expands renewable energy infrastructure to meet growing demand, balancing development with raptor conservation will require careful site selection and turbine design modifications.
Agricultural intensification brings both opportunities and threats. Increased pesticide use reduces prey populations and can cause secondary poisoning when raptors consume contaminated prey. Conversely, certain agricultural landscapes can support high raptor densities if managed appropriately. Rice paddies and wheat fields in the Terai provide excellent hunting habitat for wintering Steppe Eagles and resident Black Kites, particularly when farmers minimize chemical inputs and maintain hedgerows and scattered trees for nesting.
The illegal wildlife trade, though less prominent for Accipitridae than for some other taxa, nonetheless impacts certain species. Demand for raptors in falconry, both within South Asia and internationally, drives capture of young birds, particularly from accessible lowland nests. Body parts from eagles and vultures appear sporadically in traditional medicine markets, despite legal protections. Addressing this trade requires sustained enforcement efforts and community engagement to shift cultural attitudes toward living birds as more valuable than dead ones.
Wings of Myth: Cultural Resonance in the Himalayan Worldview
Across the cultures of the Himalaya, Accipitridae occupy positions of profound symbolic significance, bridging the terrestrial and celestial realms in ways that reflect both keen ecological observation and deeper spiritual meanings. These birds, soaring between snow-capped peaks and valley floors, become messengers between worlds, embodiments of freedom, and avatars of divine power.
The Garuda, the mythical bird-man of Hindu and Buddhist traditions, finds its earthly reflection in large eagles. Temple carvings across Nepal depict Garuda with features unmistakably derived from Aquilinae: the hooked beak, powerful talons, and commanding presence. As the vehicle of Lord Vishnu, Garuda represents the triumph of good over evil, a symbolism that resonates with eagles' ecological role as apex predators maintaining balance within their ecosystems. The annual Hadigaun Garuda festival in the Kathmandu Valley explicitly links mythological Garuda with living raptors, as priests bless eagles and hawks brought to the temple, acknowledging the sacred in the natural.
For the Sherpa and other high-altitude communities, the Lammergeier holds special significance. Its Tibetan name, Thang Chung (sky burial bird), references the species' role in traditional sky burial practices, where human remains are left on mountain platforms for consumption by vultures. Far from being macabre, this practice reflects a sophisticated understanding of ecological cycles and the Buddhist principle of giving one's body back to sustain other life. The Lammergeier's presence at these sites is considered auspicious, facilitating the deceased's journey through the bardo (intermediate state) toward rebirth. Traditional beliefs hold that harming these birds brings severe misfortune, a taboo that has afforded them informal protection even in periods when other wildlife faced heavy hunting pressure.
Among Nepal's indigenous Tharu communities of the Terai, the Brahminy Kite appears in creation stories and agricultural omens. The bird's distinctive call, described as a laughing cry, is said to predict rainfall patterns, with call frequency and intensity indicating the monsoon's strength. While such beliefs may lack scientific validation, they demonstrate intimate knowledge of the natural world and the integration of raptor ecology into agricultural decision-making systems that have sustained communities for centuries.
Shamanic traditions across the Himalaya frequently invoke raptors as spirit guides and sources of power. The ability of eagles and vultures to soar effortlessly to great heights makes them ideal symbols for spiritual ascension and the acquisition of heightened perspective. Shamans conducting healing rituals or divination often wear raptor feathers and imitate raptor calls, channeling what they perceive as these birds' connection to cosmic forces. The Tamang and Gurung communities maintain specific prohibitions against disturbing nesting eagles, believing that such disruption would invite calamity upon the entire village.
Contemporary conservation efforts increasingly recognize and engage with these cultural dimensions. Community-based conservation programs in Nepal often begin by documenting traditional ecological knowledge and belief systems surrounding raptors, using this information to develop culturally appropriate conservation messaging. When communities understand that protecting vultures aligns with both modern biodiversity goals and traditional values, conservation gains deeper legitimacy and broader support.
The cultural importance of Accipitridae extends into national symbolism. The Danphe (Himalayan Monal pheasant) may be Nepal's national bird, but eagles and vultures appear on government seals, military insignia, and currency, representing strength, sovereignty, and the wild character of the Himalayan landscape. This symbolic weight translates into political capital that conservationists can leverage when advocating for protective legislation and habitat preservation.
Horizons: The Future of Accipitridae in a Changing Himalaya
Standing at the beginning of 2026, the trajectory of Himalayan Accipitridae populations appears cautiously optimistic for some species, deeply uncertain for others. The vulture recovery, while far from complete, demonstrates that even catastrophic population collapses can be reversed when society mobilizes resources and political will. Nepal's Diclofenac-Free Zone initiative provides a template that neighboring countries are beginning to adopt, suggesting that the worst of the South Asian vulture crisis may be passing into history rather than extending into the future.
For forest specialists and high-altitude endemics, the outlook remains more ambiguous. Climate modeling suggests that suitable habitat for alpine species will continue contracting upslope, eventually leaving them with nowhere to retreat as warming accelerates. Yet these projections carry substantial uncertainty, and Accipitridae have demonstrated remarkable adaptability throughout their evolutionary history. Species currently confined to narrow elevational bands may possess greater phenotypic plasticity than current distributions suggest, potentially allowing them to track changing conditions or exploit novel habitats.
The expanding human footprint across the Himalaya will continue generating conservation challenges, but also opportunities. As Nepal develops economically, greater resources become available for protected area management, wildlife monitoring, and enforcement of environmental regulations. Growing ecotourism interest in raptor watching generates economic incentives for conservation, particularly in communities hosting vulture restaurants or along major migration corridors. The challenge lies in ensuring that development proceeds in ways that minimize habitat loss and infrastructure mortality while maximizing the economic value of living raptors to local communities.
Advances in monitoring technology promise to revolutionize our understanding of Accipitridae ecology and inform more effective conservation strategies. GPS tracking units, now small enough to deploy on medium-sized hawks, are revealing movement patterns, habitat use, and mortality sources with unprecedented precision. Camera trap networks, deployed primarily for mammal monitoring, incidentally document raptor nest sites and hunting behavior. Citizen science initiatives, particularly the growth of eBird and similar platforms in Nepal, generate vast datasets on distribution and abundance that would be impossible to collect through traditional survey methods alone.
The taxonomic revisions initiated by Catanach et al. in 2024 and continuing through 2026 carry practical conservation implications. By clarifying evolutionary relationships, these studies identify distinct populations that may warrant separate management consideration. Cryptic species (populations that appear identical but are genetically distinct and reproductively isolated) may be elevated to full species status, potentially triggering conservation attention for previously overlooked populations. Conversely, some currently recognized species may be subsumed into broader taxa, necessitating revised conservation priorities.
The greatest uncertainty surrounding Himalayan Accipitridae may lie not in environmental changes but in human choices. Will Nepal sustain its commitment to diclofenac elimination as memories of the vulture crisis fade and economic pressures mount? Will development planning incorporate wildlife considerations, or will short-term economic gains override longer-term ecological costs? Will climate change mitigation efforts proceed rapidly enough to prevent catastrophic ecosystem disruptions? The answers to these questions will determine whether the sovereigns of the Himalayan skies continue to grace these mountains for centuries to come, or whether their soaring silhouettes fade into memory and museum specimens.
The Accipitridae have survived ice ages, continental collisions, and mass extinctions over their millions of years of existence. Their adaptability, diverse hunting strategies, and occupation of every imaginable ecological niche from sea level to the stratosphere testify to evolutionary success rarely matched in the animal kingdom. Yet adaptability has its limits, and the pace of anthropogenic change now unfolds faster than natural selection can track. The fate of these magnificent birds ultimately rests not with evolution but with human stewardship, with choices made in government offices, veterinary clinics, agricultural fields, and conservation planning meetings across the Himalaya.
As thermal currents rise from the warming valleys and eagles spiral upward into the deepening blue, they carry with them the weight of evolutionary history and the uncertainty of an unwritten future. The responsibility falls to those watching from below to ensure that these sovereigns of the sky continue their ancient reign over the roof of the world.