University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USDA National Wildlife Research Center - Staff U.S. Department of Agriculture: Animal and Publications Plant Health Inspection Service 2014 Biology and Impacts of Pacific Island Invasive Species. 11. Rattus rattus, the Black Rat (Rodentia: Muridae) Aaron B. Shiels USDA, [email protected] William C. Pitt Robert T. Sugihara Gary W. Witmer USDA-APHIS-Wildlife Services, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/icwdm_usdanwrc Part of the Life Sciences Commons Shiels, Aaron B.; Pitt, William C.; Sugihara, Robert T.; and Witmer, Gary W., "Biology and Impacts of Pacific Island Invasive Species. 11. Rattus rattus, the Black Rat (Rodentia: Muridae)" (2014). USDA National Wildlife Research Center - Staff Publications. 1404. https://digitalcommons.unl.edu/icwdm_usdanwrc/1404 This Article is brought to you for free and open access by the U.S. Department of Agriculture: Animal and Plant Health Inspection Service at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USDA National Wildlife Research Center - Staff Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus, the Black Rat (Rodentia: Muridae)1 Aaron B. Shiels,2,4 William C. Pitt,2 Robert T. Sugihara,2 and Gary W. Witmer3 Abstract: The black rat, roof rat, or ship rat (Rattus rattus L.) is among the most widespread invasive vertebrates on islands and continents, and it is nearly ubiq- uitous on Pacific islands from the equatorial tropics to approximately 55 degrees latitude north and south. It survives well in human-dominated environments, natural areas, and islands where humans are not present. Rattus rattus is typically the most common invasive rodent in insular forests. Few vertebrates are more problematic to island biota and human livelihoods than R. rattus; it is well known to damage crops and stored foods, kill native species, and serve as a vector for human diseases. Rattus rattus is an omnivore, yet fruit and seed generally domi- nate its diet, and prey items from the ground to the canopy are commonly at risk and exploited as a result of the prominent arboreal activity of R. rattus. Here we review the biology of this invasive species and its impacts on humans and the insular plants and animals in the Pacific. We also describe some of the past management practices used to control R. rattus populations on islands they have invaded. Few undomesticated animals are as wide- ments across the planet is intriguing, espe- spread and well known as the black rat, Rattus cially when considering that rodents compose rattus L. (Figure 1). This rat’s behavior results over 40% of the world’s mammal species (Al- in countless negative interactions with hu- derton 1996); thus there must be some char- mans in most parts of the world, including acteristics facilitating the success of R. rattus consuming and spoiling foods, causing fires that further separate this species from the and electrical interruptions by gnawing wir- other 2,000 or more rodent species on the ing in buildings, nesting in and around human planet. Perhaps the most important charac- dwellings, and carrying diseases such as the teristic for success is that R. rattus is highly bubonic plague that has killed millions of commensal. The ability of black rats to live people ( Wilson 1968, Twigg 1978, Alderton closely and successfully with humans has fa- 1996). Human impacts and associated costs in cilitated their transport to, and establishment attempts to control or eradicate this species on, most islands in the Pacific, as well as into have continued for centuries. The success of most of the world’s biomes (Alderton 1996). R. rattus in such a range of different environ- In addition to affecting human health and economies, R. rattus is well known for its neg- ative effects on a large suite of native biota 1 Manuscript accepted 17 July 2013. and ecosystems. Rattus rattus has been identi- 2 U.S. Department of Agriculture ( USDA), Animal fied as the most damaging invasive rodent to and Plant Health Inspection Service (APHIS), National island ecosystems (Ruffino et al. 2009, Trave- Wildlife Research Center, Hawai‘i Field Station, P.O. set et al. 2009, Banks and Hughes 2012); and Box 10880, Hilo, Hawai‘i 96721. 3 USDA, APHIS, National Wildlife Research Center, globally, R. rattus is associated with the 4101 Laporte Avenue, Fort Collins, Colorado 80521. greatest number of declines or extinctions of 4 Corresponding author (e-mail: [email protected]). native island biota (Towns et al. 2006). Be- cause most of the islands in the Pacific lacked native land mammals, native flora and fauna Pacific Science (2014), vol. 68, no. 2:145 – 184 doi:10.2984/68.2.1 are particularly at risk to the negative effects © 2014 by University of Hawai‘i Press of introduced rodents such as R. rattus. Unlike All rights reserved most other introduced mammals on Pacific 145 146 PACIFIC SCIENCE · April 2014 Figure 1. Adult black rats (Rattus rattus) with (A) a black pelt and (B) a brown pelt, shown climbing a tree in native forest, O‘ahu, Hawai‘i. Note the shiny metal ear tags in both photos. (Photographs by A. B. Shiels.) islands (e.g., ungulates, dogs, cats, mongooses, and based on molecular evidence there are al- or stoats), R. rattus was unintentionally intro- most certainly multiple species within what duced to islands. has historically been identified asRattus rattus (e.g., five to seven species in the R. rattus name complex described by Robins et al. [2007] and Pagès et al. [2010], respectively). In the Mari- Rattus rattus Linnaeus, 1758 (Rodentia: Muri- dae), is commonly called the black rat, roof ana Islands, Wiewel et al. (2009) reported that rat, or ship rat. Past synonyms have included all species in their sampling that had been previously believed to be or Mus rattus Linnaeus, 1758; Mus alexandrines R. rattus R. tane- were most closely related to the Geoffroy, 1803; Musculus frugivorus Rafin- zumi R. diar- group described by Robins et al. (2007). esque, 1814; Mus novaezelandiae Buller, 1870; dii Without molecular analysis of individuals plus numerous others (Innes 2005a). In evolu- within the complex, it is very difficult tionary terms, the genus Rattus originated R. rattus about 2 – 3 million years ago (Aplin et al. to separate the species, and R. rattus and R. 2003). tanezumi are almost impossible to distinguish morphologically (Aplin et al. 2003). In addi- Rattus rattus has been separated into two subgroups based on chromosome numbers tion, three interbreeding color morphs of R. ( Yoshida et al. 1974). The Oceania group of rattus have been described in the Pacific (Tomich 1986, Innes 2005 ): R. rattus generally has 2n = 38 chromosomes a R. r. rattus (Musser and Carleton 2005), and it was this (black individuals), R. r. frugivorous (white- species that was thought to have originated in bellied), and R. r. alexandrinus (gray-bellied). the Indian Peninsula and reached Britain by For simplicity, we have not distinguished among species or color morphs within the the 3rd century A.D. (Innes 2005a). The sec- R. complex and therefore consider all of ond group of R. rattus is an Asian form that rattus those species within the complex as the black has 2n = 42 chromosomes and is indigenous to Southeast Asia; today it is also found in Ja- rat, R. rattus. pan, Taiwan, the Philippines, New Guinea, Fiji, and other islands (Robins et al. 2007). description and account of variation This Asian group is potentially multiple spe- Species Description cies and called R. tanezumi (syn. R. diardii ) by Musser and Carleton (2005). Phylogenetic re- The black rat, R. rattus, is an arboreal, ground- structuring of the “R. rattus complex” (Oce- active, and fossorial rodent that is not always anic and Asian groups) continues to progress, black in pelage (Figure 1). A recent review of Pacific Island Invasive Species:Rattus rattus, the Black Rat · Shiels et al. 147 Figure 2. Frequency of average adult body mass of Rattus rattus on Pacific island sites n( = 85 sites, representing 59 islands; latitudinal range of islands was 0 – 55 degrees). R. rattus body sizes from islands extending sexes (Innes 2005a) or slightly greater in across the Pacific basin reveals that mean males than in females (Shiels 2010). (±SE) adult body mass is 153 ± 3 g (range, Black rats, like most nocturnal rodents, 76 – 243 g; n = 85 sites, 59 islands) (Figure 2) have well-developed senses of touch, smell, (A.B.S., J. Russell, and W.C.P., unpubl. data), and hearing. Both their whiskers and guard whereas the mean adult head-body length hairs (on their pelt) are very sensitive to touch, (measured from snout to base of tail) is 175 ± 2 and they are used in orientation and move- mm (range, 134 – 207 mm; n = 71 sites, 53 is- ment in the dark. Their keen sense of smell lands) (A.B.S., J. Russell, and W.C.P., unpubl. allows them to find food and water, detect data). These Pacific-wide R. rattus body size sexually active individuals, and distinguish measurements were similar to those summa- foreign and familiar individuals and locations rized across New Zealand (Innes 2005a). (Mallick 1992, Innes 2005a,b). They have Unlike other invasive Rattus species ( Yom- round, dark eyes that are specialized for noc- Tov et al. 1999, Atkinson and Towns 2005), turnal vision; their eyes are very sensitive to there does not appear to be a Pacific-wide light, but their vision is not acute (Innes pattern of greater body size with increasing 2005a). latitude for R.