Written By Kathleen Burns

The hippopotamus is listed as a vulnerable species and is facing serious anthropogenic threats in Africa.[1] Across the Atlantic Ocean, however, hippos are thriving in the Magdalena River basin of Colombia, making them the largest invasive animal in the world.[2] Their devastating impact on the surrounding environment presents an ethical dilemma for Colombian authorities and the international communities: how to address the hippo in the room.  

Hippos were introduced to Colombia courtesy of international drug kingpin Pablo Escobar. In the 1980s, Escobar imported three female hippos and one male hippo to decorate his estate, Hacienda Nápoles.[3] Following Escobar’s death and collapse of his drug empire in 1993, the four hippos evaded capture and escaped into the surrounding Magdalena Riven basin.[4] The hippos flourished in the Magdelena wetlands, enjoying the abundant resources and relative safety provided by the Magdalena River basin.[5] 

In the years since, the hippo population and expansion has grown exponentially. A study used a predictive model of the persistence of the invasive hippo population under different scenarios of management found that the population of exotic hippos in Colombia has been steadily growing at a rate of 14.5%.[6]  At that rate, the study concluded that the hippo population could reach 1500 by 2040 if stronger measures are not put in place to control the population.[7] While the growing population of hippos currently occupies 2000 square kilometers of the Magdelena basin,[8] hippos could occupy the entire Magdalena River basin if the population cannot be controlled.[9] 

The invasive hippo population creates significant harm to the surrounding environment.[10] Native species, such as capybaras, must compete with the invasive hippos for resources and space.[11] Hippos can also carry zoonotic diseases and parasites, which can be transmitted to wild animals, domestic animals, and even humans.[12] On a deeper level, the mere presence of hippos causes changes in oxygen dynamics, biogeochemistry, and sedimentation rates in the watershed, which could favor some species and negatively affect others.[13] Additionally, hippos engage in behavior such as wallowing, scouring, and compressing the bottom of water bodies, which has significant effects on geomorphology and hydrology. These effects could be critical for vulnerable migratory species such as the Antillean manatee,[14] particularly during the dry season.[15]

Despite their popularity as a tourist attraction, the hippos also threaten local economies.[16] They destroy and consume agricultural products, compete with livestock, and harm the diversity and abundance of fishes.[17] As suggested by reports of hippo attacks in Colombia, conflict between humans and the invasive hippos is inevitable.[18] Hippos are naturally territorial and aggressive,[19] accounting for one-quarter of all wildlife related casualties in Africa and kill more people yearly than any other African mammal.[20] As hippo populations continue to grow and spread into more developed areas, ecologists predict that hippo attacks resulting in injury or even death will become more common.[21]

Finding a solution to the problem has generated a fierce ethical debate. Ecologists argue that culling the invasive hippo population is the best strategy to protect the ecology of the Magdalena River basin,[22] but this argument has drawn serious opposition from animal rights activists.[23] The debate is further complicated by a judicial decision in Colombian courts which recognized five principles of animal welfare [24] and prohibited culling by granting legal personhood to the invasive hippos.[25] To address this dilemma, international law, specifically the Biodiversity Convention, may provide the necessary guidance to strike an appropriate balance between ecological welfare and animal rights.  

The Biodiversity Convention defines invasive alien species (IAS) as “species introduced via human action outside of their natural geographical range, with a demonstrable environmental or socio-economic impact and capable of sustaining a self-replacing population.”[26] Article 8(h) of the Biodiversity Convention requires member states, such as Colombia to control or eradicate IAS which threaten ecosystems, habitats or species.[27] The Guiding Principles recognized that IAS represent one of the primary threats to biodiversity and reaffirmed the importance of national and regional IAS strategies and action plans.[28] Guiding Principle 12 suggests that States should “individually and cooperatively” take appropriate steps such as eradication, containment, and control to “mitigate adverse effects.”[29] Guiding Principle 12 also provides that “techniques used for eradication, containment or control should be safe to humans, the environment and agriculture as well as ethically acceptable to stakeholders in the areas affected by the invasive alien species.”[30] 

There are four broad strategies applied to invasive alien species: prevention, eradication, containment, and control.[31] When it comes to control, Guiding Principle 15 provides that “effective control will often rely on a range of integrated management techniques… implemented according to existing national regulations.” Currently, Colombia is pursuing two principal strategies to control the invasive hippos: translocation and sterilization. While these strategies are “ethically acceptable,” the strategies are ineffective and therefore cannot sufficiently control the hippo population as required by Article 8(h).[32]

Sending the hippos back to their native habitat in Africa is not a viable translocation strategy under current international guidelines due to the risk of introducing harmful, invasive viruses and bacteria to the African ecosystem.[33] The translocation strategy taken by Colombia instead involved moving hippos to zoo and animal sanctuaries in India and Mexico.[34] A total of 70 hippos are expected to be translocated, with 60 going to India and 10 to Mexico.[35] However, locating and safely capturing the hippos has been challenging.[36] Transportation is a long and costly process,[37] and the relocation project in its entirety would cost about $3.5 million.[38] Yet this program may not be sufficient. Even at an annual extraction rate of 20 individuals, the population is projected to recover in 2042 to a size of 1500 individuals.[39] However, it is estimated that an annual extraction rate of thirty hippos per year would lead to complete eradication in just a few years.[40] The rate, however, may only be possible through culling.[41]

Colombia has also participated in initiatives to sterilize both male and female hippos as part of a strategy to control the hippo population. Sterilization efforts are difficult and costly to implement, and currently ineffective, especially as locating and sterilizing male hippos via castration in an intensive process.[42] Additionally, ecologists argue that there has not been an “important impact on reproduction” as a result of the castration initiatives.[43] One study even suggests that the current population size has grown two to three times larger in just eight years.[44] The study concluded that exponential population growth is still expected under this approach.[45]

For females, Colombia has initiated a fertility control program, which involves the use of a drug to reduce the fertility of female hippos.[46] 70% to 80% of the female hippos would need to be treated with the drug for the strategy to be effective, and treatments run about $50,000 USD for each hippo.[47] This is a long-term strategy, which will reduce the number of hippos over time, but cannot completely eradicate the hippos.[48] 

For these reasons, Colombia cannot meet its obligations under Article 8(h) using only these strategies. The strategies cannot eradicate the hippos completely.[49] The only way to achieve control or eradication in many cases is through culling the invasive alien species. Indeed, many States in dealing with invasive alien species have resorted to mass culling efforts. Consider the lionfish, an invasive alien species wreaking havoc on reef systems in the Caribbean. In an attempt to control the population and spread of the poisonous fish, many affected states encourage competitive fishing and the introduction of lionfish into local diets.[50]

Yet Guiding Principle 12 clearly required solutions that are ethically acceptable to stakeholders,[51] and Colombia has determined that massive culling efforts are not an “ethical solution.” After eradication strategies involving culling the hippos drew outrage from animal rights activists and locals who view the hippos as a economically beneficial tourist attraction,[52] Colombia recognized the ability of animals to exercise legal rights in their own name and established five principles of animal welfare: freedom from hunger or thirst; freedom from discomfort; freedom from pain, injury, or disease; freedom to express normal behavior; and freedom from fear and distress by ensuring conditions and treatment which avoid mental suffering.[53]  This decision gave the hippos the right to be free from cruelty and exploitation, and effectively prevented the hippos from being culled.[54] 

However, culling the hippos is an ethical solution when the same legal framework established by the Colombian court is applied to native species living in the Magdalena River basin, and the interests of native species are taken into account. It must be assumed that the capybara, manatee, and other members of the river basin ecosystem deserve the same consideration as “sentient beings” affording to the “charismatic megafauna” threatening their home. Under the five principles of animal welfare established by Colombian courts, the native species deserve freedom from hunger or thirst, but native species have to compete with the invasive hippos for resources. Native species deserve freedom from disease, but are threatened by the zoonotic diseases carried by the invasive hippos. Native species deserve to express normal behavior, but cannot do so when they are forced to adapt to the invasive hippos. The rights of other species and the wider biosphere must be considered when making strategic decisions. Even those who are opposed to culling the hippos recognize that biodiversity is at risk if Colombia fails to effectively reduce the hippo population.[55] The welfare of a single invasive species should not outweigh the interests of an entire ecosystem.[56] The legal and ethical argument for culling the hippos should be centered not around an “anthropogenic sense of convenience,”[57] but around the rights of all animals in an ecosystem. It may therefore be a “necessary evil” to humanely cull invasive species to ensure the welfare of native species.[58] Arguing otherwise fails to consider the “social picture, the economic picture, and the ecological picture.”[59]

In order to balance the interests of the invasive hippos, the native ecosystem, and local communities pursuant to the Biodiversity Convention, Colombia should pursue a tri-pronged strategy of translocation, culling, and movement control. The first prong of the strategy, translocation, would allow the hippos to be relocated as planned to zoos and conservation centers in India and Mexico. This would reduce the remaining hippo population and preserve the interests of the hippos in accordance with domestic law, as suggested by Guiding Principle 15.[60]

 The second prong of the strategy would address the welfare of the ecosystem by culling the hippos that have spread too far. This would protect the interests of the native species and preserve the welfare of the ecosystem, ensuring effective mitigation of the adverse environmental impacts caused by the expanding hippo population. This would be consistent with Guiding Principle 1361 and, if the ethical concerns can be sufficiently addressed, Guiding Principle 12.[62]

The final prong of the strategy would take into account community interests by creating a wildlife center in Hacienda Nápoles to house a small, controlled population of hippos controlled through the already established fertility methods. The region would be able to retain a popular tourist attraction, making the eradication efforts outside the wildlife center more acceptable. The wildlife center would allow for close monitoring of the hippos while simultaneously educating the public on the dangers of invasive species. The wildlife center should be created and managed with input from indigenous and local communities. 

As with any solution to this complex issue, this strategy is far from perfect. However, by intensifying current efforts and adopting new strategies, Colombia can meet its obligation under Article 8(h) and successfully control the invasive hippo population to preserve biodiversity and ecological welfare in the Magdalena River basin. 

Works Cited

[1] See Delma Nataly Castelblanco-Martínez, et al., A Hippo in the Room: Predicting the Persistence and Dispersion of an Invasive Mega-Vertebrate in Colombia, South America, 253 Biological Conservation 1, 2 (2021).

[2] See id.

[3] See Elliot Doornbos, Pablo Escobar’s ‘Cocaine Hippos’ are a Problem – but a Lot of Thought is Going into Preventing Their Spread, The Conversation (Apr. 18, 2023, 12:12 PM EDT), https://theconversation.com/pablo-escobars-cocaine-hippos-are-a-problem-but-a-lot-of-thought-is-going-into-preventing-their-spread-203603.

[4] See Castelblanco-Martínez, supra note 1.

[5] See Doornbos, supra note 3; Castelblanco-Martínez, supra note 1, at 8 (noting the Magdalena River basin provides a suitable habitat with abundant forage and lacking disease, predation, or anthropogenic threats).

[6] See id. at 10.

[7] See id. at 8.

[8] See id. at 2.

[9] See id. at 6.

[10] See id. at 9.

[11] See Sarah Kaplan, Invasion of the Hippos: Colombia is Running Out of Time to Tackle Pablo Escobar’s Wildest Legacy, Wash. Post. (Jan. 11, 2021, 12:16 PM EST), https://www.washingtonpost.com/climate-environment/2021/01/11/invasive-hippos-escobar-colombia-castrate/.

[12] See Castelblanco-Martínez, supra note 1, at 9.

[13] See id. (noting also that hippo urine and feces significantly increase the phosphates and nitrogen concentration in the water, which could create potentially toxic cyanobacteria)

[14] See Kaplan, supra note 11.

[15] See Castelblanco-Martínez, supra note 1, at 9.

[16] See id. at 3 (noting that livelihoods of local communities are intimately linked to riverine ecosystem dynamics).

[17] See id. at 9.

[18] See Kaplan, supra note 11.

[19] See Elliot Doornbos, Colombian Hippos and Species Management: Exploring the Legal Case Surrounding the Management and Control of the Colombian Hippos from a Species Justice Perspective, 12: 29 Laws (Special Issue) 1, 3 (2023) [hereinafter Species Justice Perspective].

[20] See Castelblanco-Martínez, supra note 1, at 9.

[21] See id.

[22] See id. at 10.

[23] See Species Justice Perspective, supra note 19, at 7.

[24] See id. at 6.

[25] See Castelblanco-Martínez, supra note 1, at 2.

[26] See id. at 1.

[27] See Convention on Biological Diversity art. 8(h), Jun. 5, 1992, 31 I.L.M. 818.

[28] See UNEP/CBD/COP/6/20, Annex I.

[29] Id.

[30] Id.

[31] See Species Justice Perspective, supra note 19.

[32] See Castelblanco-Martínez, supra note 1, at 10.

[33] See Ángela Reyes Haczek & Kathleen Magrama, Colombia Plans to Send 70 ‘Cocaine Hippos’ to India and Mexico, Governor Says, CNN (Mar. 4, 2023, 2:34 AM EST), https://www.cnn.com/2023/03/04/americas/colombia-cocaine-hippos-pablo-escobar-india-mexico-intl-hnk/index.html; Castelblanco-Martínez, supra note 1, at 8.

[34] See Elliot Doornbos, supra note 3.

[35] See Haczek, supra note 33.

[36] See Castelblanco-Martínez, supra note 1, at 10.

[37] See id.

[38] See Elliot Doornbos, supra note 3.

[39] See Castelblanco-Martínez, supra note 1, at 9.

[40] See id.

[41] See id. at 10.

[42] See Kaplan, supra note 11.

[43] See Castelblanco-Martínez, supra note 1, at 2.

[44] See id.

[45] See id.

[46] See Doornbos, supra note 3.

[47] See id.

[48] See Haczek, supra note 33 (reporting that contraceptive drives have had limited success); Castelblanco-Martínez, supra note 1, at 9 (concluding increasing sterilization rates will lead to delay in fast-growth phase but fail to completely eradicate the hippo population).

[49] See UNEP/CBD/COP/6/20, Annex I.

[50] See D.T. Max, Killing Invasive Species is Now a Competitive Sport, New Yorker (Sep. 5, 2022), https://www.newyorker.com/magazine/2022/09/12/killing-invasive-species-is-now-a-competitive-sport.

[51] See UNEP/CBD/COP/6/20, Annex I.

[52] See Malaika Tareen, Legal Rights of Nature: Do Ecosystems Carry Legal Standing?, Climate & Env. Init. (May 17, 2022), https://cei.rsilpak.org/blog/legal-rights-of-nature-do-ecosystems-carry-legal-standing/; Sarah Kaplan, Invasion of the Hippos: Colombia is Running Out of Time to Tackle Pablo Escobar’s Wildest Legacy, Wash. Post. (Jan. 11, 2021, 12:16 PM EST), https://www.washingtonpost.com/climate-environment/2021/01/11/invasive-hippos-escobar-colombia-castrate/.

[53] See Species Justice Perspective, supra note 19, at 6.

[54] See Tareen, supra note 52.

[55] See id. (acknowledging that failing to address invasive species arguably goes against current frameworks of ecology and environmental justice).

[56] See Kaplan, supra note 52 (reporting concerns that management of the hippos takes resources away from vulnerable and endangered species in Colombia); see also Species Justice Perspective, supra note 19, at 10 (describing the hippo case as an anomaly due to national and international attention on charismatic megafauna).

[57] See id.

[58] See id.

[59] See Kaplan, supra note 11.

[60] See UNEP/CBD/COP/6/20, Annex I.

[61] See id.

[62] See id.

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