By Allegra Tennis, Smithsonian Libraries Hay Intern
In the 1960s, the men of the Smithsonian’s Pacific Ocean Biological Survey Program (POBSP) traveled to many small islands of the Pacific Ocean. The aim was to conduct extensive biological surveys of the area, with a heavy emphasis on banding migratory birds. In the course of studying bird life, they encountered a problem – invasive species. These harmful species are especially dangerous to the remote islands of the Pacific, which are often home to very rare and endangered animals.
Many of the islands of the Pacific have issues with invasive non-native species, the main ones being cats, rats, and snakes. The introduction of rats and snakes were accidental; the creatures stowed away on ships, and quickly adapted to their new territory when they made landfall. The introduction of cats was more intentional, they were brought to islands already overrun by rats or mice, and were meant as a way to control the rodent population. Native bird species, some of which are (or were) flightless, were easy prey to these invaders. Their numbers suffered significantly, and in some cases, led to the extinction of the species.
Invasive species are often successful because of a lack of natural predators in their new habitat. Their population increases exponentially until it reaches its carrying capacity, the maximum amount of individuals that an area is able to sustain. Populations that exceed their carrying capacity due to unchecked growth have the tendency to be less healthy than other populations, due to competition over food resources, and the spread of disease.
One of the islands visited by POBSP researchers was Jarvis Island, an uninhabited minor outlying island of the United States which has a particular history of being plagued by feral cats. Many of the scientists make note of the felines, such as Charles Douglas Hackman, who observed in his field journal on March 14, 1964, “this super abundance of cats has undoubtedly discouraged several species from nesting on the island.”
Field catalog from Jarvis Island, Fred Sibley. Smithsonian Institution Archives. RU000245, Box 245, Volume 69. Image courtesy of Allegra Tennis.
The POBSP researchers did not originally set out to study cats, but they could not turn off their scientific brains when it came to making small observations. In his field notes, Hackman compares the Jarvis cat population to felines on other Pacific islands, and notes how much healthier the Jarvis cats are. He speculates that their population is nearing its carrying capacity, but has not yet quite reached it. This hypothesis was supported by observations of how healthy and well-fed the Jarvis cats were, all with stomachs full of the native birds. In comparison, Hackman comments on how cats of other islands appeared weaker, less energetic, and with emptier stomachs.
Field catalog from Jarvis Island, Fred Sibley. Smithsonian Institution Archives. : RU 000245 National Museum of Natural History, Pacific Ocean Biological Survey Program, records, circa 1961-1973, with data from 1923; Box 245, Volume 69. Image courtesy of Allegra Tennis.
After banding birds on Jarvis Island all day, many of the POBSP researchers would set out to remove the unwelcome cats. Excerpts from several POBSP journals, including Hackman’s, estimate that the feline population was reduced by over two-thirds in their time on the island. These men express regret that they could not stay longer to ensure that Jarvis was once again inhabited only by its native birds.
About twenty years later, two men came to Jarvis Island with the goal of doing just that. Mark Rauzon and David Woodside arrived in 1982, and after multiple visits over the course of several years, succeeded in freeing Jarvis Island from its cat problem. Rauzon recounts this tale in more detail in his book, Isles of Amnesia. Today, Jarvis Island is a U.S. National Wildlife Refuge, a designation that will, it is hoped, keep other invasive species far away from its vulnerable bird populations.
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Rauzon, M. J. (2016). Isles of amnesia. Honolulu, HI: University of Hawai'i Press.
Smith, R. (2013, July 29). Rat invaders: Islands fighting back against killer rodents [Electronic version]. National Geographic.
Smithsonian National Zoological Park. (n.d.). "Where have the birds of Guam gone?" Meet our animals. Retrieved from https://nationalzoo.si.edu/Animals/Birds/Facts/fact-guambirds.cfm
United States Department of Agriculture. (2011). "Brown Tree Snake: An invasive reptile." Animal and Plant Health Inspection Service. Retrieved from https://www.aphis.usda.gov/publications/wildlife_damage/content/printable_version/fs_brown_tree_snake_2011.pdf
United States Department of Agriculture. (2016). "National invasive species information center." National agricultural library. Retrieved July 15, 2016, from https://www.invasivespeciesinfo.gov/index.shtml