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This article is about the species of rodent. For other uses, see Black rat (disambiguation).

Black rat
Temporal range: Holocene
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Muridae
Genus: Rattus
Species:
R. rattus
Binomial name
Rattus rattus
Synonyms

Mus rattus Linnaeus, 1758

The black rat (Rattus rattus), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus Rattus, in the subfamily Murinae.[1] It likely originated in the Indian subcontinent, but is now found worldwide.[2]

The black rat is black to light brown in colour with a lighter underside. It is a generalist omnivore and a serious pest to farmers because it feeds on a wide range of agricultural crops. It is sometimes kept as a pet. In parts of India, it is considered sacred and respected in the Karni Mata Temple in Deshnoke.

Taxonomy

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Mus rattus was the scientific name proposed by Carl Linnaeus in 1758 for the black rat.[3]

Three subspecies were once recognized, but today are considered invalid and are now known to be actually colour morphs:[citation needed]

  • Rattus rattus rattus – roof rat
  • Rattus rattus alexandrinus – Alexandrine rat
  • Rattus rattus frugivorus – fruit rat

Characteristics

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Skull
Comparison of physique with a brown rat (Rattus norvegicus)
Black rat skeleton (Museum of Osteology)
Museum of Osteology

A typical adult black rat is 12.75 to 18.25 cm (5.02 to 7.19 in) long, not including a 15 to 22 cm (5.9 to 8.7 in) tail, and weighs 75 to 230 g (2.6 to 8.1 oz), depending on the subspecies.[4][5][6][7] Black rats typically live for about one year in the wild and up to four years in captivity.[5] Despite its name, the black rat exhibits several colour forms. It is usually black to light brown in colour with a lighter underside. In England during the 1920s, several variations were bred and shown alongside domesticated brown rats. This included an unusual green-tinted variety.[8]

Origin

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The black rat was present in prehistoric Europe and in the Levant during postglacial periods.[9] The black rat in the Mediterranean region differs genetically from its South Asian ancestor by having 38 instead of 42 chromosomes.[10] Its closest relative is the Asian house rat (R. tanezumi) from Southeast Asia. The two diverged about 120,000 years ago in southwestern Asia. It is unclear how the rat made its way to Europe due to insufficient data, although a land route seems more likely based on the distribution of European haplogroup "A". The black rat spread throughout Europe with the Roman conquest, but declined around the 6th century, possibly due to collapse of the Roman grain trade, climate cooling, or the Justinianic Plague. A genetically different rat population of haplogroup A replaced the Roman population in the medieval times in Europe.[11]

It is a resilient vector for many diseases because of its ability to hold so many infectious bacteria in its blood. It was formerly thought to have played a primary role in spreading bacteria contained in fleas on its body, such as the plague bacterium (Yersinia pestis) which is responsible for the Plague of Justinian and the Black Death.[12] However, recent studies have called this theory into question and instead posit humans themselves as the vector, as the movements of the epidemics and the black rat populations do not show historical or geographical correspondence.[13][14] A study published in 2015 indicates that other Asiatic rodents served as plague reservoirs, from which infections spread as far west as Europe via trade routes, both overland and maritime. Although the black rat was certainly a plague vector in European ports, the spread of the plague beyond areas colonized by rats suggests that the plague was also circulated by humans after reaching Europe.[15]

Distribution and habitat

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The black rat originated in India and Southeast Asia, and spread to the Near East and Egypt, and then throughout the Roman Empire, reaching Great Britain as early as the 1st century AD.[16] Europeans subsequently spread it throughout the world. The black rat is again largely confined to warmer areas, having been supplanted by the brown rat (Rattus norvegicus) in cooler regions and urban areas. In addition to the brown rat being larger and more aggressive, the change from wooden structures and thatched roofs to bricked and tiled buildings favoured the burrowing brown rats over the arboreal black rats. In addition, brown rats eat a wider variety of foods, and are more resistant to weather extremes.[17]

Black rat populations can increase exponentially under certain circumstances, perhaps having to do with the timing of the fruiting of the bamboo plant, and cause devastation to the plantings of subsistence farmers; this phenomenon is known as mautam in parts of India.[18]

Black rats are thought to have arrived in Australia with the First Fleet, and subsequently spread to many coastal regions in the country.[19]

Black rats adapt to a wide range of habitats. In urban areas they are found around warehouses, residential buildings, and other human settlements. They are also found in agricultural areas, such as in barns and crop fields.[20] In urban areas, they prefer to live in dry upper levels of buildings, so they are commonly found in wall cavities and false ceilings. In the wild, black rats live in cliffs, rocks, the ground, and trees.[21] They are great climbers and prefer to live in palms and trees, such as pine trees. Their nests are typically spherical and made of shredded material, including sticks, leaves, other vegetation and cloth. In the absence of palms or trees, they can burrow into the ground.[22] Black rats are also found around fences, ponds, riverbanks, streams, and reservoirs.[23]

Behaviour and ecology

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It is thought that male and female rats have similarly sized home ranges during the winter, but male rats increase the size of their home range during the breeding season. Along with differing between rats of different sex, home range also differs depending on the type of forest in which the black rat inhabits. For example, home ranges in the southern beech forests of the South Island, New Zealand appear to be much larger than the non-beech forests of the North Island. Due to the limited number of rats that are studied in home range studies, the estimated sizes of rat home ranges in different rat demographic groups are inconclusive.

Diet and foraging

[edit]
Black rat eating grain

Black rats are considered omnivores and eat a wide range of foods, including seeds, fruit, stems, leaves, fungi, and a variety of invertebrates and vertebrates. They are generalists, and thus not very specific in their food preferences, which is indicated by their tendency to feed on any meal provided for cows, swine, chickens, cats and dogs.[23] They are similar to the tree squirrel in their preference of fruits and nuts. They eat about 15 g (0.53 oz) per day and drink about 15 ml (0.53 imp fl oz; 0.51 US fl oz) per day.[22] Their diet is high in water content.[23] They are a threat to many natural habitats because they feed on birds and insects. They are also a threat to many farmers, since they feed on a variety of agricultural-based crops, such as cereals, sugar cane, coconuts, cocoa, oranges, and coffee beans.[24]

The black rat displays flexibility in its foraging behaviour. It is a predatory species and adapts to different micro-habitats. It often meets and forages together in close proximity within and between sexes.[25] It tends to forage after sunset. If the food cannot be eaten quickly, it searches for a place to carry and hoard to eat at a later time.[23] Although it eats a broad range of foods, it is a highly selective feeder; only a restricted selection of the foods is dominating.[26] When offered a wide diversity of foods, it eats only a small sample of each. This allows it to monitor the quality of foods that are present year round, such as leaves, as well as seasonal foods, such as herbs and insects. This method of operating on a set of foraging standards ultimately determines the final composition of its meals. Also, by sampling the available food in an area, it maintains a dynamic food supply, balance its nutrient intake, and avoids intoxication by secondary compounds.[26]

Nesting behaviour

[edit]

Through the usage of tracking devices such as radio transmitters, rats have been found to occupy dens located in trees, as well as on the ground. In Puketi Forest in the Northland Region of New Zealand, rats have been found to form dens together. Rats appear to den and forage in separate areas in their home range depending on the availability of food resources.[25] Research shows that, in New South Wales, the black rat prefers to inhabit lower leaf litter of forest habitat. There is also an apparent correlation between the canopy height and logs and the presence of black rats. This correlation may be a result of the distribution of the abundance of prey as well as available refuges for rats to avoid predators. As found in North Head, New South Wales, there is positive correlation between rat abundance, leaf litter cover, canopy height, and litter depth. All other habitat variables showed little to no correlation.[27] While this species' relative, the brown (Norway) rat, prefers to nest near the ground of a building the black rat will prefer the upper floors and roof. Because of this habit they have been given the common name roof rat.

Diseases

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Black rats (or their ectoparasites[28]) can carry a number of pathogens,[29] of which bubonic plague (via the Oriental rat flea), typhus, Weil's disease, toxoplasmosis and trichinosis are the best known. It has been hypothesized that the displacement of black rats by brown rats led to the decline of the Black Death.[30][31] This theory has, however, been deprecated, as the dates of these displacements do not match the increases and decreases in plague outbreaks.[32][33][34]

Rats serve as outstanding vectors for transmittance of diseases because they can carry bacteria and viruses in their systems. A number of bacterial diseases are common to rats, and these include Streptococcus pneumoniae, Corynebacterium kutsheri, Bacillus piliformis, Pasteurella pneumotropica, and Streptobacillus moniliformis, to name a few. All of these bacteria are disease causing agents in humans. In some cases, these diseases are incurable.[35]

Predators

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The black rat is prey to cats and owls in domestic settings. In less urban settings, rats are preyed on by weasels, foxes and coyotes. These predators have little effect on the control of the black rat population because black rats are agile and fast climbers. In addition to agility, the black rat also uses its keen sense of hearing to detect danger and quickly evade mammalian and avian predators.[23]

As an invasive species

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Damage caused

[edit]

After Rattus rattus was introduced into the northern islands of New Zealand, they fed on the seedlings, adversely affecting the ecology of the islands. Even after eradication of R. rattus, the negative effects may take decades to reverse. When consuming these seabirds and seabird eggs, these rats reduce the pH of the soil. This harms plant species by reducing nutrient availability in soil, thus decreasing the probability of seed germination. For example, research conducted by Hoffman et al. indicates a large impact on 16 indigenous plant species directly preyed on by R. rattus. These plants displayed a negative correlation in germination and growth in the presence of black rats.[36] Rats prefer to forage in forest habitats. In the Ogasawara islands, they prey on the indigenous snails and seedlings. Snails that inhabit the leaf litter of these islands showed a significant decline in population on the introduction of Rattus rattus. The black rat shows a preference for snails with larger shells (greater than 10 mm), and this led to a great decline in the population of snails with larger shells. A lack of prey refuges makes it more difficult for the snail to avoid the rat.[37]

Complex pest

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The black rat is a complex pest, defined as one that influences the environment in both harmful and beneficial ways. In many cases, after the black rat is introduced into a new area, the population size of some native species declines or goes extinct. This is because the black rat is a good generalist with a wide dietary niche and a preference for complex habitats; this causes strong competition for resources among small animals. This has led to the black rat completely displacing many native species in Madagascar, the Galapagos, and the Florida Keys. In a study by Stokes et al., habitats suitable for the native bush rat, Rattus fuscipes, of Australia are often invaded by the black rat and are eventually occupied by only the black rat. When the abundances of these two rat species were compared in different micro-habitats, both were found to be affected by micro-habitat disturbances, but the black rat was most abundant in areas of high disturbance; this indicates it has a better dispersal ability.[38]

Despite the black rat's tendency to displace native species, it can also aid in increasing species population numbers and maintaining species diversity. The bush rat, a common vector for spore dispersal of truffles, has been extirpated from many micro-habitats of Australia. In the absence of a vector, the diversity of truffle species would be expected to decline. In a study in New South Wales, Australia it was found that, although the bush rat consumes a diversity of truffle species, the black rat consumes as much of the diverse fungi as the natives and is an effective vector for spore dispersal. Since the black rat now occupies many of the micro-habitats that were previously inhabited by the bush rat, the black rat plays an important ecological role in the dispersal of fungal spores. By eradicating the black rat populations in Australia, the diversity of fungi would decline, potentially doing more harm than good.[38]

Control methods

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Large-scale rat control programs have been taken to maintain a steady level of the invasive predators in order to conserve the native species in New Zealand such as kokako and mohua.[39] Pesticides, such as pindone and 1080 (sodium fluoroacetate), are commonly distributed via aerial spray by helicopter as a method of mass control on islands infested with invasive rat populations. Bait, such as brodifacoum, is also used along with coloured dyes (used to deter birds from eating the baits) in order to kill and identify rats for experimental and tracking purposes. Another method to track rats is the use of wired cage traps, which are used along with bait, such as rolled oats and peanut butter, to tag and track rats to determine population sizes through methods like mark-recapture and radio-tracking.[25] Tracking tunnels (coreflute tunnels containing an inked card) are also commonly used monitoring devices, as are chew-cards containing peanut butter.[40] Poison control methods are effective in reducing rat populations to nonthreatening sizes, but rat populations often rebound to normal size within months. Besides their highly adaptive foraging behaviour and fast reproduction, the exact mechanisms for their rebound is unclear and are still being studied.[41]

In 2010, the Sociedad Ornitológica Puertorriqueña (Puerto Rican Bird Society) and the Ponce Yacht and Fishing Club launched a campaign to eradicate the black rat from the Isla Ratones (Mice Island) and Isla Cardona (Cardona Island) islands off the municipality of Ponce, Puerto Rico.[42]

Decline in population

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Eradication projects have eliminated black rats from Lundy in the Bristol Channel (2006)[43] and from the Shiant Islands in the Outer Hebrides (2016).[44] Populations probably survive on other islands (e.g. Inchcolm) and in localised areas of the British mainland.[45] Recent National Biodiversity Network data shows a very sparse populations around the U.K.[46], and the Mammal Society has no records in the major port towns of Manchester, Liverpool or Glasgow for over 40 years[47], areas which were historically population strongholds.

See also

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References

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Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Black rat

View on Grokipedia
from Grokipedia
The black rat (Rattus rattus), also known as the roof rat, ship rat, or house rat, is a slender, arboreal in the family , native to the and . It features a body length of 16–22 cm, a tail exceeding head and body length at 18–25 cm, large dark eyes, prominent rounded ears, a pointed muzzle, and soft, glossy fur typically ranging from blackish to brownish-gray. Adults weigh 150–250 g, with exceptional climbing agility enabling it to navigate trees, walls, and roofs. As an opportunistic , it primarily consumes fruits, seeds, grains, vegetation, , and occasionally small vertebrates or carrion, often foraging at night. Originally confined to , the black rat has become one of the world's most widespread invasive mammals through human-mediated dispersal, particularly via maritime trade since ancient times, establishing populations on every continent except and in diverse environments from tropical forests to urban centers. It thrives in warm, humid climates but adapts to temperate zones, preferring elevated habitats like tree canopies, attics, and palm fronds over ground-level burrows, though it competes with the larger rat (Rattus norvegicus) in cooler areas. Ecologically, black rats exhibit high reproductive rates, with females reaching at about 3 months and producing up to 5 litters annually, each containing 5–8 young after a 21–23 day , leading to exponential population growth in favorable conditions. Their is hierarchical, with individuals marking territories using and communicating via ultrasonic vocalizations. As a commensal species closely associated with human settlements, the black rat exerts significant ecological and economic impacts, including predation on native birds, eggs, and —especially on islands, where it contributes to extinctions—and damage to through crop consumption and contamination. It serves as a reservoir and vector for numerous zoonotic pathogens, transmitting diseases such as , , , and plague via urine, feces, bites, or ectoparasites like fleas and ticks. Historically implicated in pandemics like the 14th-century , modern control efforts focus on , including rodenticides, trapping, and habitat modification to mitigate its role in and risks.

Taxonomy and phylogeny

Taxonomy

The black rat, scientifically known as Rattus rattus (Linnaeus, 1758), belongs to the family , genus , and subgenus within the order . Originally described by in his , the species was initially classified under the genus Mus as Mus rattus, reflecting early taxonomic groupings of before the establishment of the genus by Fischer de Waldheim in 1803. Other historical synonyms include Mus alexandrinus (Geoffroy, 1803) and Musculus frugivorus (Rafinesque, 1814), which were later synonymized under Rattus rattus as taxonomic revisions clarified distinctions within the family. Historically, several of R. rattus have been recognized based on coat color, morphology, and geographic origin, such as R. r. rattus, R. r. alexandrinus, and R. r. frugivorus. However, ongoing taxonomic revisions treat these as color morphs or forms within the broader R. rattus , which may encompass 4-6 distinct including R. tanezumi. These lineages are often distinguished by karyotypes, with the widespread invasive form having 38 chromosomes (2n=38), while Asian forms like R. tanezumi have 42 chromosomes (2n=42). The traditional nominate form R. r. rattus is associated with and characterized by a slaty-black dorsal coat and grayish ventral pelage; the R. r. alexandrinus form, prevalent in tropical regions of , features a grayish-brown back and pure white underparts, adapted to commensal habitats along trade routes. Another variant, the R. r. frugivorus form, occurs in oceanic islands and exhibits a brownish dorsum with matching ventral coloration, reflecting adaptations to insular environments. These forms highlight the black rat's wide dispersal, often via human-mediated transport, contrasting with its close relative, the ( norvegicus), which shares the but occupies different ecological niches.

Phylogenetic relationships

The black rat (Rattus rattus) belongs to the genus Rattus within the subfamily Murinae of the family Muridae, commonly known as Old World rats or true rats, which originated and diversified in Asia. This placement positions the black rat in the tribe Rattini, a diverse group of murine rodents characterized by specific morphological and genetic traits distinguishing them from other rodent subfamilies. Phylogenetic analyses using mitochondrial and nuclear DNA sequences consistently support this classification, highlighting the black rat's close relation to other Asian Rattus species within the Murinae clade. Molecular clock studies estimate the genetic divergence between the black rat and the (Rattus norvegicus) at approximately 1.94 million years ago, marking a significant split within the genus during the . This divergence is inferred from whole-genome sequencing and from archaeological sites, revealing distinct lineages that reflect adaptations to different ecological niches in . Such estimates align with broader phylogenetic reconstructions of the , which indicate that species began radiating in southern and southeastern around 2-3 million years ago. Fossil records of species, including those attributable to the R. rattus complex, date to the late and in , with key specimens from sites in and southern supporting an origin. These fossils, such as dental remains from Khao Phlo in , demonstrate the early presence of Rattus-like murines in tropical Asian environments, predating global dispersals. Palaeontological evidence from the and further suggests late migrations of black rat ancestors from westward, consistent with the species' Asian cradle. The black rat exhibits hybridization potential with closely related Rattus species, such as R. tanezumi in the R. rattus complex, leading to and the formation of hybrid sub-lineages that complicate phylogenetic resolution. Historical invasions, as seen in , have facilitated between oceanic and Asian black rat groups, influencing and evolutionary trajectories within the . This hybridization underscores the dynamic nature of Rattus phylogeny, where reticulate evolution via interbreeding has shaped lineage boundaries and adaptation in commensal populations.

Physical characteristics

Morphology and physiology

The black rat (Rattus rattus) is a medium-sized with a body length ranging from 16 to 22 cm, a measuring 19 to 25 cm—typically longer than the body—and an average weight of 150 to 250 g. Its fur is sleek and typically or dark gray on the dorsal side, often fading to lighter gray, brown, or pale yellow on the ventral surface, though color variations including or white morphs occur depending on geographic populations and environmental factors. Distinctive features include large, prominent eyes adapted for low-light conditions, relatively large and thin ears for enhanced auditory detection, and a long, scaly that provides balance and prehensile grip during movement. Physiologically, the black rat exhibits excellent agility suited to its primarily arboreal lifestyle, with skeletal adaptations such as a narrow , flexible spine, and strong limb musculature enabling efficient climbing and leaping among trees and structures. Its sensory capabilities are highly developed, featuring a keen via an extensive for detecting food and predators from afar, and acute hearing that includes sensitivity to ultrasonic frequencies for communication and environmental cues. The species maintains a high metabolic rate, with a of approximately 0.77 W, supporting its energetic demands for foraging and rapid reproduction in diverse habitats. These climbing adaptations facilitate its preference for elevated, arboreal habitats where it avoids ground-based threats. Sexual dimorphism in the black rat is minimal, primarily manifesting as males being slightly larger and heavier than females, with differences in body length and mass typically under 10-15% on average.

Reproduction and development

The black rat (Rattus rattus) is polyestrous, capable of breeding year-round under favorable conditions, though reproductive activity often peaks in warmer months. Females typically produce 3 to 6 litters per year, with an inter-litter interval as short as 30 days depending on food availability. Gestation lasts 21 to 24 days, after which a litter of 6 to 12 altricial young is born, with averages ranging from 5 to 8 pups reported across populations. Litter size can be influenced by maternal nutrition, where abundant resources lead to larger broods. Black rats reach rapidly, with females attaining it at 2 to 3 months (approximately 80 to 90 days) and males slightly later at around 3 to 4 months. In the wild, their lifespan is short, averaging 1 to 2 years due to high predation and environmental pressures, while individuals in can live up to 5 years. This fast reproductive cycle contributes to their high potential in suitable habitats. Newborn black rats are altricial, born hairless, blind, and helpless in concealed nests constructed by the mother. Eyes open around 15 days, and occurs at 3 to 4 weeks, by which time the young begin exploring independently but remain dependent on the nest for protection. Dispersal typically happens at 2 to 3 months, coinciding with , as juveniles leave to establish new territories. Parental care is provided solely by females, who nurse the litter for about 3 weeks, retrieve wandering pups, and aggressively defend the nest from intruders. Males offer no involvement in rearing, focusing instead on opportunities. This maternal supports high juvenile rates in protected environments.

Origins and distribution

Evolutionary origins

The black rat ( rattus), a member of the subfamily of , has its evolutionary roots in , with native lineages distributed across the , including western and eastern , the Himalayan region, and extending into southern and northern Indochina as well as . Phylogenetic analyses indicate that the genus diverged from other murids approximately 3.5 million years ago, with the R. rattus complex emerging around 1 million years ago during the Pleistocene. These origins tie the black rat closely to other Asian murids, reflecting a shared biogeographic history in tropical and subtropical environments, with phylogenetic studies revealing multiple independent origins of across its native lineages in . Archaeological evidence from fossil and subfossil remains confirms the black rat's presence in early human contexts dating back to the period, approximately 7000–2000 BCE. In the , commensal R. rattus bones have been recovered from multiple sites in the Indus Valley, such as those in northwest , indicating cohabitation with prehistoric agricultural communities. Similarly, remains from settlements in island , dated to approximately the same era, suggest the species' early association with human activity in its native range, predating widespread global introductions. The black rat's adaptation to a commensal likely coevolved with the rise of early human in , allowing it to exploit stored grains and waste in permanent settlements. This behavioral shift facilitated its initial dispersal beyond native habitats via ancient overland and maritime trade routes, such as those connecting the to the and well before the European , with genetic and archaeogenetic data supporting multiple waves of expansion tied to human economic networks starting in the to , around the 3rd millennium BCE.

Global distribution and habitats

The black rat (Rattus rattus), native to the , has achieved a cosmopolitan distribution, having been introduced to all continents except primarily through human-mediated shipping routes since antiquity, with major waves during the Roman and medieval periods in and later to the , , and other regions from the 15th century onward. This species is now widespread across diverse regions, including , North and , , , and numerous oceanic islands, often arriving as stowaways on vessels. Its global presence is closely tied to human activities, particularly maritime trade and transportation, enabling establishment in both continental and insular environments. Black rats exhibit versatile habitat preferences, commonly inhabiting urban and peri-urban areas, tropical and subtropical forests, and even ship holds where they can persist during long voyages. They display strong arboreal tendencies, frequently nesting and foraging in trees, attics, roof spaces, and elevated structures within buildings, which provides protection from ground-based predators. While adaptable to a range of environments, they avoid open aquatic or sewer habitats, favoring instead sheltered, structurally complex sites that support their climbing and leaping behaviors. The occupies an altitudinal range from to approximately 2,500 m, as observed in regions like where it thrives across varied elevations. Black rats tolerate a broad spectrum of climates but are most abundant in warm, humid conditions typical of tropical and subtropical zones, where reproductive rates and survival are optimized. In cooler temperate areas, their populations are limited by physiological constraints and . Recent distributional shifts reflect ongoing environmental and anthropogenic influences, with expansions noted in rapidly urbanizing regions facilitated by climate warming and increased human density, which enhance food availability and connectivity. Conversely, in temperate zones, black rat ranges have contracted due to competitive displacement by the more cold-tolerant (Rattus norvegicus), leading to their reduced prevalence in cooler urban and rural settings. These dynamics underscore the species' sensitivity to both climatic and biotic factors in shaping its contemporary .

Behavior and ecology

Daily behavior and social structure

The black rat (Rattus rattus) exhibits primarily nocturnal and crepuscular activity patterns, with and exploratory behaviors concentrated during nighttime hours when visibility for predators is reduced and resources are more accessible. During the day, individuals typically rest in elevated nests constructed in trees, attics, or other high structures, minimizing exposure to ground-based threats. This diurnal resting habit aligns with their arboreal adaptations, allowing them to conserve energy and avoid or predation. Socially, black rats form loose rather than tightly knit groups, often comprising 10–50 individuals in favorable habitats, where dominance hierarchies emerge to regulate access to resources and . Males establish and defend territories through aggressive interactions, with dominant individuals gaining priority in opportunities and spatial control, while subordinate males occupy peripheral areas. Females tend to be less territorial but integrate into these hierarchies based on proximity to resources. These structures promote colony stability but can lead to intra-specific conflicts, particularly during resource scarcity. Communication among black rats relies heavily on olfactory and acoustic signals to maintain social bonds and territorial boundaries. Scent marking via and sebaceous gland secretions from the flanks and anogenital region conveys individual identity, reproductive status, and dominance, with males marking more frequently to assert . Acoustically, they produce a repertoire of at least 10 distinct vocalizations, including five ultrasonic signals in the 20–70 kHz range, emitted during social interactions, situations, or mating contexts to coordinate group activities without alerting predators. These multimodal cues facilitate efficient information exchange in dense or complex environments. In terms of activity patterns, black rats demonstrate high mobility within their home ranges, which average 0.3–0.6 hectares for females and up to 1.87 hectares for males in varied habitats, enabling extensive nightly exploration. In urban settings, individuals may traverse distances of up to 200 meters per night, navigating vertical and horizontal spaces via climbing and jumping to access food sources and nesting sites. This mobility supports rapid dispersal and adaptation but also contributes to their invasive potential in human-modified landscapes.

Diet and foraging strategies

The black rat (Rattus rattus) exhibits an omnivorous diet dominated by plant material, which typically constitutes 94–98% of its intake, including seeds, fruits, nuts, and vegetation. This plant-based component reflects the species' adaptability to diverse environments, where it preferentially consumes available resources such as fruits and seeds in insular habitats. Animal matter supplements the diet, comprising 2–6% overall, primarily arthropods and occasionally small vertebrates like birds or , though this varies by location and prey availability. Foraging strategies of the black rat are highly opportunistic, allowing it to exploit temporary food surpluses and adjust to fluctuating resources. Individuals often cache excess food in hidden locations, such as burrows or elevated sites, to store seeds and nuts for later consumption, a observed in both captive and wild populations. Due to its arboreal tendencies, the black rat preferentially in elevated positions like canopies or roofs, reducing exposure to ground-dwelling predators such as snakes or carnivores. This vertical foraging minimizes competition with terrestrial species and enhances access to canopy fruits and . Nutritional adaptations enable efficient processing of its varied diet, with the digestive tract featuring a simple stomach and suited to omnivory. The black rat produces salivary for breakdown, facilitating rapid digestion of and grains that form dietary staples. Essential vitamin requirements, including and from plant sources, support metabolic needs, though deficiencies can arise in monotonous diets. Seasonal variations in diet occur, with a shift toward increased animal matter during periods of scarcity, such as dry seasons or mast failures. In resource-poor conditions, consumption of and small vertebrates rises to meet protein demands, demonstrating the ' flexible trophic niche. As an , this foraging adaptability can indirectly pressure local by selective .

Predation and disease transmission

The black rat (Rattus rattus) is preyed upon by a variety of predators, including such as hawks and , as well as mammals like cats, weasels, foxes, skunks, dogs, snakes, and even conspecifics such as Norway rats (Rattus norvegicus). Humans also pose a threat through and . The black rat's arboreal adaptations, including exceptional climbing agility, enable it to evade many ground-dwelling predators by seeking refuge in trees, attics, and rafters. Black rats act as significant vectors for multiple zoonotic pathogens, facilitating disease transmission to humans and other animals. They carry , the bacterium responsible for plague, which is primarily transmitted through bites from infected fleas such as the (Xenopsylla cheopis). Additionally, they harbor hantaviruses, including the Seoul virus, spread via contact with contaminated urine, droppings, or saliva, often through inhalation of aerosolized particles. , caused by bacteria, is transmitted through exposure to the rats' urine-contaminated or soil, entering the body via mucous membranes or cuts. Bites from infected rats can also directly spread certain pathogens like . Historically, black rats played a pivotal role in major pandemics, most notably the of 1347–1352, where their fleas disseminated Y. pestis across , contributing to an estimated 25–50 million deaths and severe demographic collapse. The rats' spread along trade routes amplified the epidemic's geographical reach, making plague endemic in until the 18th century. Their commensal association with human settlements has driven evolutionary adaptations, including partial to pathogens like Y. pestis, allowing them to serve as reservoirs that sustain transmission cycles without high mortality. This tolerance likely arose from long-term co-evolution in urban environments, where exposure to diverse microbes selected for modulated immune responses. In urban habitats, black rats' proximity to human populations heightens the risk of pathogen spillover, exacerbating disease outbreaks in densely populated areas.

Invasive impacts

Ecological damage

The black rat (Rattus rattus), as an , inflicts significant ecological damage on native , particularly on islands where it has been introduced, by preying on vulnerable , competing with endemic species, and altering habitats through and burrowing activities. These impacts disrupt food webs, reduce , and hinder ecosystem recovery, often leading to cascading effects on communities and populations. One of the most severe consequences is through direct predation on eggs and chicks, which has contributed to the of numerous island-endemic . Invasive , including black rats, are linked to the of 52 bird worldwide, primarily on oceanic islands where ground-nesting seabirds lack evolved defenses against mammalian predators. Black rats target eggs and nestlings opportunistically, consuming them at high rates and resulting in near-total breeding failure for affected colonies and population collapses. This predation extends to other vertebrates, such as and small mammals, further eroding native faunal diversity. Black rats also engage in intense competition with native for and , particularly in Pacific island ecosystems, where they displace endemic species through interference and resource dominance. In littoral rainforests, black rats outcompete native bush rats (Rattus fuscipes) by exploiting arboreal niches and superior foraging efficiency, leading to reduced population densities and range contraction of the natives. Similar dynamics occur in the Galápagos, where black rats limit the recovery of endemic small mammals like the Santiago rice rat (Nesoryzomys swarthi) by competing for seeds and , slowing seasonal population growth even after predator removal efforts. Habitat alteration arises primarily from seed predation, which disrupts plant regeneration and forest structure, compounded by soil disturbance from burrowing. Black rats consume large quantities of seeds, removing up to 89% over short periods (e.g., 5 days) on northern islands in podocarp-broadleaf forests, which lowers seedling richness and density while favoring weedy species that tolerate disturbance. Their foraging scatters and caches uneaten seeds, but high predation rates prevent establishment of canopy trees, altering successional trajectories; additionally, burrowing loosens and promotes in fragile island soils. In the , black rats, introduced by European sailors in the 1600s, have profoundly impacted endemic biodiversity since their arrival, preying on seabird nests and hatchlings while competing with native . This has halted population recovery for like the Pinzón giant (Chelonoidis duncanensis), with rats consuming eggs and juveniles, and contributed to nest failures in the critically endangered Galápagos (Pterodroma phaeopygia), as documented by camera traps showing direct predation events. In , black rats arrived with European colonization in the 1700s–1800s and have driven local extinctions, such as on Big South Cape Island in 1964, where a single introduction led to the extinction of two bird (South Island and Stead's bush wren), the greater short-tailed bat, and multiple invertebrates through predation and habitat disruption. Ongoing impacts include widespread nest raiding of native birds like the kiwi (Apteryx spp.), exacerbating declines in forest ecosystems.

Economic and health consequences

The black rat (Rattus rattus) causes extensive agricultural damage worldwide by directly consuming crops and contaminating them with , , and hair, leading to significant economic losses. It preferentially targets grains such as and , as well as fruits like coconuts, bananas, and , particularly in tropical and subtropical farming regions where it thrives as an invasive pest. These activities result in both pre- and post-harvest losses, with invasive —including black rats—responsible for reported global costs totaling at least US$3.6 billion from 1930 to 2022, though actual figures are likely much higher due to underreporting. Beyond , black rats inflict structural damage to through their constant gnawing , which is necessary to prevent overgrowth of their incisors. They chew through electrical wires, creating fire hazards and short circuits; wooden beams, doors, and walls in buildings; and insulation materials, compromising structural integrity. Additionally, their of stores and water sources with pathogens and waste amplifies economic burdens by necessitating costly cleaning, disposal, and repairs. Black rats pose major threats as reservoirs for zoonotic diseases, transmitting pathogens that cause outbreaks in densely populated areas. They are primary carriers of species, leading to —a potentially fatal infection spread via urine-contaminated water or soil—which is especially prevalent in urban tropical settings with inadequate . For example, studies in Brazilian urban slums have shown strong associations between black rat infestations and elevated leptospirosis incidence. Historically, black rats also facilitated plague transmission during 19th-century pandemics, exacerbating health crises amid grain destruction that worsened famines in affected regions.

Control and management

Control and management of black rat (Rattus rattus) populations primarily rely on integrated pest management (IPM) strategies that combine sanitation, structural exclusion, and direct population reduction to minimize environmental and health risks posed by this invasive species. Sanitation involves removing food sources and harborage, such as clearing debris and securing waste, while exclusion uses rodent-proof barriers like metal flashing on buildings and trees to prevent access. These non-chemical approaches form the foundation of IPM, reducing reliance on lethal controls and addressing the black rat's arboreal habits in urban and agricultural settings. Population reduction within IPM often employs and rodenticides. Snap traps placed in bait stations on a 25 m × 25 m grid have proven effective for eradication, achieving up to 97% success over extended periods in fragmented landscapes, with larger rats removed first and low recolonization rates observed. rodenticides, such as or diphacinone, are commonly applied via broadcast baiting or stations; combining diphacinone bait with snap trapping yields higher efficacy than baiting alone in orchards. For eradications, aerial application of has successfully eliminated black rats from sites like , where no rats were detected post-treatment, leading to recovery. Biological controls offer sustainable alternatives, particularly in conservation contexts. Barn owls (Tyto alba) serve as effective predators, consuming significant numbers of black rats in agricultural and semi-urban areas; installing nest boxes can enhance their impact without chemical use. However, risks to non-target species, such as endangered birds, must be mitigated through careful placement. Fertility control trials, including contraceptive baits like those containing , have shown promise in reducing black rat reproductive potential by inducing in both sexes after consumption. Prevention focuses on halting new invasions, especially on and via maritime pathways. Ship inspections, including rat guards on lines and thorough vessel checks for signs of , are standard protocols to block black stowaways. Post-eradication, quarantines enforce measures like restricted access and surveillance to prevent reinvasion; since the , these have supported over 580 successful rat eradications globally, including more than 100 targeting black rats on tropical . Challenges in black rat management include evolving resistance to anticoagulants like , observed in populations where higher doses were needed for blood-clotting inhibition, necessitating alternative rodenticides or multi-method approaches. In conservation areas, ethical concerns arise from potential animal suffering in or , as well as non-target impacts; welfare assessments recommend humane dispatch methods and monitoring to balance eradication benefits with minimal harm.

Population dynamics

Historical introductions

The black rat (Rattus rattus), native to and adapted to commensal living with humans, began its human-mediated global dispersal in antiquity through expanding networks. Its arrival in is associated with Roman expansion and urban development starting in the CE, as evidenced by from archaeological sites in , , and Britain, indicating multiple introductions tied to Mediterranean routes. Similarly, the species reached via maritime from along routes, with genetic and archaeological evidence from sites in eastern , such as Unguja Ukuu in , dating introductions to as early as the CE, likely through commerce involving the and ports. During the colonial era from the 15th to 19th centuries, European maritime exploration and dramatically expanded the black rat's range worldwide, as the species stowed away on ships carrying provisions and cargo. In the , black rats arrived with early European voyages, including Columbus's expeditions in the late 15th century, establishing populations along coastal settlements by the 1500s, as confirmed by zooarchaeological remains from sites in the and eastern . This period marked the species' proliferation across the Atlantic and Pacific, facilitated by transoceanic shipping that connected , , , and the , leading to widespread establishment in port cities and agricultural areas. In the 20th century, modern shipping and air travel further accelerated the black rat's dispersal, enabling rapid introductions to remote islands and urban centers previously inaccessible. Containerized cargo and aviation hubs served as vectors, contributing to invasions in regions like and oceanic islands, where genetic studies show ongoing admixture from diverse source populations. Notable historical introductions include the species' arrival in Australia during the late 18th and early 19th centuries via European vessels, with the First Fleet in 1788 likely carrying black rats to Sydney, and subsequent shipwrecks and pearling operations spreading them to offshore islands by the 1800s. In the Pacific, while Polynesians introduced related Rattus species around 1000 CE, black rats reached Hawaii in the 19th century through European and American ships, establishing invasive populations that persist today.

Current declines and conservation

Historically, in many urban and temperate regions, black rat (Rattus rattus) populations experienced significant declines up to the mid-20th century primarily due to intense competition with the (Rattus norvegicus), which is better adapted to ground-dwelling in human-modified environments and displaced black rats from preferred niches. Habitat loss from and agricultural intensification further exacerbated these reductions by fragmenting arboreal habitats that black rats favor. Successful eradication programs on islands and coastal areas have also contributed to localized population crashes, often targeting black rats to protect native . Regionally, black rat numbers decreased substantially in and from the early onward, following the widespread establishment of around the , leading to near-complete replacement in many urban settings. In contrast, populations remain stable or are increasing in tropical regions, where black rats thrive in forested and agricultural landscapes with less competition from and where human activities like can enhance invasion opportunities. As of 2025, recent studies indicate resurgence in black rat populations in some urban areas of and , with increases exceeding 10% in cities like since 2014, driven by climate warming that extends breeding seasons and that boosts food availability, though dominance persists in cooler ground-level niches. From a conservation perspective, black rats hold no endangered status and are instead managed as , with efforts focused on their removal to safeguard threatened island endemics such as seabirds and reptiles. The International Union for Conservation of Nature (IUCN) supports numerous eradication initiatives on tropical islands, exemplified by successful operations on in , which have restored habitats for without broader protections for black rats themselves. Looking ahead, is projected to expand black rat ranges northward into previously unsuitable temperate zones by warming winters and extending breeding seasons, with urban growth further facilitating population booms despite competition from brown rats.

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