The Silent Island: A “Tail” of Ecosystem Collapse
Stepping into the forests on the island of Guam, one may notice that something critically important is missing: the sound of birds. The cause of this silence is the invasive non-native predator, the Brown treesnake, which was introduced to the island after World War II. The ecological cascade following the arrival of this species parallels Rachel Carson’s 1962 book, Silent Spring, which explores the consequences of the pesticide DDT on bird reproduction and the resulting deficit of birds and bird calls. The DDT issue was resolved in part by action from the U.S. Similarly, the situation on Guam will require greater intervention by the U.S. than current efforts.
Impacts on Guamanian Ecosystems
The introduction of snakes to Guam has had an incredible impact on biodiversity, especially for native bird species. By 1987, ten out of twelve forest bird species no longer existed on the island. The Micronesian Starling, or såli, is one of species that has persisted on Guam. However, a 2019 study found that 56% of fledgling mortality for the såli was due to predation by treesnakes. This pressure will increase if treesnake populations continue to grow.
Furthermore, the decimation of native birds has had cascading effects across the whole island. A 2008 study of two bird-pollinated native plant species found that pollination and seed production were significantly higher on the neighboring island of Saipan compared to Guam. Because Saipan has no snakes, bird populations are intact and pollinators are available for the bird-pollinated plants. The reduction in vegetation on the island likely has other far-reaching effects that scientists have yet to quantify.
Impacts on People and Culture
Aside from ecological changes, treesnakes have also damaged the cultural heritage of Guam. One of these impacts is on a non-native plant called the donne’ såli, or chili pepper. The word såli in donne’ såli might sound familiar, for good reason; this is a reference to the såli birds, one of the species negatively affected by treesnakes. A 2017 study found that a decline in the såli lead to a decline in peppers because the pepper seeds are meant to be dispersed by birds. For the CHamoru, the donne’ såli peppers are most often wild-collected due to difficulty of cultivation and a perceived higher spice level in wild plants. While not native to the island, the wild donne’ såli is crucial to the flavor profile of many local foods and is therefore highly valued by the CHamoru, so its scarcity has been notable.
Another such setback occurred when the official bird of Guam was listed as “extinct in the wild” due to the Brown treesnake. The Guam rail — or Ko’ko’ to the indigenous CHamorus — is endemic to Guam, so this was an upset to the CHamorus as the charismatic, flightless bird was a representative for the entire island. Fortunately, this species has rebounded thanks to a rehabilitation project on the nearby islands of Cocos and Rota and is now listed as “critically endangered.” While the Ko’ko’ has not yet been reintroduced to Guam, the future of this species seems promising.
Next Steps
The ecology of Guam cannot revert to its original state without intervention, in yet another parallel to Rachel Carson’s Silent Spring. The U.S. initiated a ban on DDT in 1972, 10 years after the book was published, allowing damaged ecosystems to recover in the U.S. Likewise, Guam needs more intervention by the U.S. government to eradicate the Brown treesnake and recover native biodiversity. The U.S. can no longer ignore the ecology of Guam and the impact of invasive species on native CHamorus and Guam residents, both of whom are citizens of the U.S.
Scientists are actively testing new mechanisms to eradicate treesnakes across the island. Areas of research include testing aerial bait delivery and different baits like artificial fats or acetaminophen. However, fixing the situation on Guam is not the priority of those in charge. The U.S. government is working to prevent further invasions and resulting ecosystem collapses in different areas outside of Guam. USGS has stated that “Preventing the spread of the invasive Brown treesnake is paramount.” The Department of the Interior has made that clear through the allocation of funds to fight the snakes. $3.4 million in total was provided by the U.S. government in 2020 to control snake populations. $1.2 million of that was for the control and research of existing populations, half a million was for outreach, and $1.7 million went toward the prevention of new populations. More effort should be spent trying to fix the issue created for Guam by the U.S. This goal is supported by the United Nations October 2021 claim that it is a human right to have access to a healthy environment. While the U.S. is not currently in the United Nations, it should strive to protect all human rights, especially for U.S. citizens and for people whose land they occupy. The current U.S. perspective sees Guam’s ecology as a low priority and it is not acceptable.
Citations
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Carson, Rachel. Silent Spring. Mariner Books (Houghton Mifflin), 2002.
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Pervasive Impacts of Invasive Brown Treesnakes Drive Low Fledgling Survival in Endangered Micronesian Starlings (Aplonis Opaca) on Guam. https://doi-org.proxy.library.ucsb.edu:9443/10.1093/condor/duz014. Accessed 15 Oct. 2021.
Mortensen, Hanne Skovgaard, et al. “A Snake in Paradise: Disturbance of Plant Reproduction Following Extirpation of Bird Flower-Visitors on Guam.” Biological Conservation, vol. 141, no. 8, Aug. 2008, pp. 2146–54. ScienceDirect, https://doi.org/10.1016/j.biocon.2008.06.014.
Egerer, Monika H., et al. “Seed Dispersal as an Ecosystem Service: Frugivore Loss Leads to Decline of a Socially Valued Plant, Capsicum Frutescens.” Ecological Applications, vol. 28, no. 3, 2018, pp. 655–67. Wiley Online Library, https://doi.org/10.1002/eap.1667.
Howard, Jenny. “How an Interloper Snake Decimated Guam’s Delicious Wild Chilies.” Massive Science, 2 Mar. 2018, https://massivesci.com/articles/guam-chili-birds-snakes/.
Guam Rail - Guam - U.S. Fish and Wildlife Service. https://www.fws.gov/nwrs/threecolumn.aspx?id=2147526078. Accessed 16 Oct. 2021.
Siers, Shane. In Situ Evaluation of an Automated Aerial Bait Delivery System for Landscape-Scale Control of Invasive Brown Treesnakes on Guam. p. 10.
How Is the USGS Helping to Prevent the Spread of the Brown Treesnake? https://www.usgs.gov/faqs/how-usgs-helping-prevent-spread-brown-treesnake?qt-news_science_products=0#qt-news_science_products. Accessed 16 Oct. 2021.
Interior Announces $3.4 Million for Brown Tree Snake Control on Guam. 3 June 2020, https://www.doi.gov/oia/press/interior-announces-34-million-brown-tree-snake-control-guam.
Farge, Emma. “UN Declares Access to a Clean Environment a Human Right.” Reuters, 8 Oct. 2021. www.reuters.com, https://www.reuters.com/business/environment/un-passes-resolution-making-clean-environment-access-human-right-2021-10-08/.