The Black Rat is one of two species of rats found in British Columbia, both introduced and considered invasive. Despite its name, the Black Rat has several colour forms: it may be black to light grey-brown in colour with a lighter that ranges from slate grey to white (Nagorsen 2005). It has a slender body and large hairless ears and a noticeably long tail that is longer than the head and body combined. Its smaller size and the long tail separate it from the Norway Rat.
The Black Rat is a social, nocturnal species often found in groups. It is a good climber (view a photo) and, while often found on the ground, it is more often arboreal. It is easily observed at night as it moves along fences, gutters and power lines (Nagorsen 2005, Wikipedia 2012). It is an omnivorous species, and eats a variety of foods, including insects, snails, and spiders, but shows a preference for grains. It is sometimes observed on raspberry and blackberry branches feeding on berries (see photo). Nagorsen (2005) says: "On the Queen Charlotte Islands, Black Rats feed on the eggs and chicks of ground-nesting seabirds, such as the Ancient Murrelet."
The Black Rat originates in tropical Asia (subcontinental India and Pakistan) and is now found on all continents: it thrives in tropical areas. It generally does not do well in temperate regions where it is out-competed by the Norway Rat, but is reported to be successful in some temperate areas (Animal Diversity Web, 2014). It is a species that does well around human habitation and on ships, and is frequently found in coastal areas, however the domestic cat is a major predator in urban and agricultural areas.
The Black Rat is found in Canada only in British Columbia--primarily in agricultural and urban areas (Nagorsen 2005, Wikipedia 2012). Its exact date of arrival in BC is unknown, although the earliest collections from the province were by Lord in 1858 (Nagorsen 2005). However, it is now reported from greater Vancouver, the lower Fraser Valley, the Queen Charlotte Islands, Vancouver Island and Cortes Island (but is absent from other islands adjacent to Vancouver Island). Although initially found primarily around dumps and waterfront areas, "on southern Vancouver Island and in North Vancouver it is found in forested habitats well away from human dwellings" (Nagorsen 2005). Nagorsen (2005) reports this species is less common than BC's other species of rat--the Norway Rat (Rattus norvegicus).
Three subspecies of the Black Rat have been recognized in BC in the past, however, all three are currently recognized as colour phases in a polymorphic species (Nagorsen 2005).
The Global Invasive Species Database (2014) provides the following taxonomic information on the Black Rat: "The work of Yosida (1980) and his co-workers has shown that there are two forms of R. rattus that differ in chromosome number. The more widespread Oceanic form has 38 chromosomes and is the ship rat of Europe, the Mediterranean region, America, Australia and New Zealand. Present indications are that it is the Oceanic form that has reached islands in the South Pacific, but studies are needed to confirm this. The Asian form has probably reached some islands north of the equator, e.g. the Caroline Islands. On the basis of colour variation in rats on Ponape and Koror Islands, described by Johnson (1962) as Rattus rattus mansorius, we suspect that these rats may be the Asian form of R. rattus (SPREP, 2000)."
In their 1958 publication Alien Animals of British Columbia, Carl and Guiguet summarize the species occurrence in BC at that time: "This species apparently arrived later than the Norway Rat (dates unknown), but it cannot compete with that species where it comes in contact. It is less common than the Norway Rat in most areas of the province, but it is well-established on the Queen Charlotte Islands and the mountains adjacent to Vancouver..."
"Rats are resilient vectors for many diseases because of their ability to hold so many infectious bacteria in their blood. Rats played a primary role in spreading bacteria, such as Yersinia pestis, which is responsible for the Justinianic plague and bubonic plague." (Wikipedia 2012)