rats

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Rats have become a significant issue for the Dutch Caribbean islands. In addition to being disease vectors, these island invaders can also dramatically upset the delicate ecological balance on the islands by devouring bird eggs, and outcompeting local species for food and other resources.  

Photo credit: Joshua J. Cotten

There is perhaps no species more widespread than the rat. These rodents were unintentionally introduced to the Dutch Caribbean by human activity, tracing back to the early colonial era when ships brought goods  and unknowingly stowaway rats, to these shores. With no natural predators and abundant food sources, rats quickly adapted and multiplied, triggering an ecological imbalance with far-reaching consequences.

Ecological Impacts

One of the most significant impacts of rats in the Dutch Caribbean is their voracious appetite for bird eggs. Many local bird species, such as the endemic, Red-billed tropicbird and several species of protected terns, nest on the ground, making their eggs highly vulnerable to predation.

Nesting adult red-billed Tropicbird with chick.
Photo credit: Michiel Boeken

The implications of rat predation on bird eggs are multifaceted. Firstly, it disrupts the reproductive success of avian species, leading to population declines and, in extreme cases, local extinctions. Birds that lose their eggs or young are less likely to breed again in the same season, hampering population recovery. The loss of bird species not only diminishes the islands’ natural beauty but also disrupts the delicate ecological balance for the islands.

Beyond the direct impact on bird populations, the loss of eggs due to rat predation has cascading effects on the broader ecosystem. Birds play crucial roles as pollinators, seed dispersers, and predators of insects. When bird populations decline, the natural dynamics become disrupted, leading to an imbalance in plant reproduction, changes in insect populations, and altered food chains.

Disease Vectors 

These rodents are also notorious carriers of diseases. Due to their tendency to live within waste and sewage, coupled with their highly mobile nature, rats’ urine, droppings, and bites, can transmit a wide range of illnesses, including leptospirosis, hantavirus, salmonellosis, and rat-bite fever. Rats can also carry ticks, mites and fleas which are potential vectors of disease for both people as well as local animal populations.

Photo credit: Christine McCall

Mitigating the Impact

Recognizing the urgency of the situation, conservation organizations and local park authorities have undertaken initiatives to combat the invasive rat populations within the Dutch Caribbean. Examples of local efforts includes the Caribbean Netherlands Science Institute’s 2017 Rodent Control Project on St. Eustatius as well as research conducted on Saba to better understand the impacts of rats on local bird populations. These efforts focus on implementing comprehensive strategies that combine education, habitat management, and targeted rat eradication programs.

DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports science communication and outreach in the Dutch Caribbean region by making nature-related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the (in) direct impacts resulting from publishing this article.

Ratten zijn een groot probleem geworden voor de Nederlands Caribische eilanden. Behalve dat ze ziekteverspreiders zijn, kunnen deze eilandindringers ook het delicate ecologische evenwicht op de eilanden dramatisch verstoren door vogeleieren te verslinden en lokale soorten te overtroeven voor voedsel en andere hulpbronnen.

Foto: Joshua J. Cotten

Er is misschien geen soort die zo wijdverbreid is als de rat. Deze knaagdieren werden onbedoeld door menselijke activiteit in de Nederlandse Cariben geïntroduceerd. Deze activiteiten gaan terug tot het vroege koloniale tijdperk toen schepen goederen en onbewust ratten naar deze kusten brachten. Zonder natuurlijke roofdieren en overvloedige voedselbronnen, pasten ratten zich snel aan en vermenigvuldigden ze zich, wat leidde tot een ecologische onevenwichtigheid met verstrekkende gevolgen.

Ecologische effecten

Een van de belangrijkste effecten van ratten in de Nederlandse Cariben is hun vraatzuchtige honger naar vogeleieren. Veel lokale vogelsoorten, zoals de endemische roodsnavelkeerkringvogel en verschillende soorten beschermde sterns, nestelen op de grond, waardoor hun eieren zeer kwetsbaar zijn voor predatie.

Nestelende volwassen roodsnavelkeerkringvogel met jong. Foto: Michiel Boeken

De implicaties van rattenpredatie op vogeleieren zijn veelzijdig. Ten eerste verstoort het het voortplantingssucces van vogelsoorten, wat leidt tot populatieafname en, in extreme gevallen, lokale uitsterving. Vogels die hun eieren of jongen verliezen, broeden minder vaak in hetzelfde seizoen, wat het herstel van de populatie belemmert. Het verlies van vogelsoorten tast niet alleen de natuurlijke schoonheid van de eilanden aan, maar verstoort ook het delicate ecologische evenwicht van de eilanden.

Naast de directe invloed op vogelpopulaties, heeft het verlies van eieren als gevolg van predatie door ratten trapsgewijze effecten op het bredere ecosysteem. Vogels spelen een cruciale rol als bestuivers, zaadverspreiders en roofdieren van insecten. Wanneer vogelpopulaties afnemen, wordt de natuurlijke dynamiek verstoord, wat leidt tot een onevenwichtigheid in de reproductie van planten, veranderingen in insectenpopulaties en veranderde voedselketens.

Ziekteverspreiders

Deze knaagdieren zijn ook beruchte dragers van ziekten. Vanwege hun neiging om in afval en rioolwater te leven, in combinatie met hun zeer mobiele aard, kunnen urine, uitwerpselen en beten van ratten een breed scala aan ziekten overdragen, waaronder leptospirose, hantavirus, salmonellose en rattenbeetkoorts. Ratten kunnen ook teken, mijten en vlooien bij zich dragen, die potentiële ziekteverspreiders zijn voor zowel mens als lokale dierenpopulaties.

Foto: Christine McCall

De invloed beperken

De urgentie van de situatie erkennend, hebben natuurbeschermingsorganisaties en lokale parkautoriteiten initiatieven genomen om de invasieve rattenpopulaties in Caribisch Nederland te bestrijden. Voorbeelden van lokale inspanningen zijn het Rodent Control Project van het Caribisch Nederlands Wetenschappelijk Instituut uit 2017 op Sint Eustatius en onderzoek op Saba om de effecten van ratten op lokale vogelpopulaties beter te begrijpen. Deze inspanningen zijn gericht op het implementeren van alomvattende strategieën die onderwijs, habitatbeheer en gerichte programma’s voor de uitroeiing van ratten combineren.

DCNA

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschapscommunicatie en outreach in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en de pers. Dit artikel bevat de resultaten van verschillende wetenschappelijke onderzoeken, maar de onderzoeken zelf zijn geen DCNA-onderzoeken. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de (in)directe gevolgen die voortvloeien uit het publiceren van dit artikel.

Published in BioNews 67

Since the furry stowaways landed here aboard sealing and whaling ships in the 19th century, they've been wreaking ecological havoc on the island and its ground-nesting seabirds by preying on the birds and their eggs.

Enter an international team of wildlife biologists, who have recently completed the second phase of history's largest rat-eradication program on the remote island.

Braving appalling weather in the run-up to the Antarctic winter, the group's helicopter pilots logged hundreds of hours in perilous flying conditions to spread nearly 200 tons of rat poison over 224 square miles (580 square kilometers) of South Georgia's coastline.

The ultimate goal: To rid this once supreme seabird habitat of its millions of rats once and for all. South Georgia was probably the richest seabird-breeding area in the world when British Captain James Cook visited it in 1775, according to Tony Martin of the University of Dundee, who leads the rat-eradication campaign on behalf of the South Georgia Heritage Trust. (See more pictures of South Georgia.)

Now the island has less than one percent of its original seabird population, he said. "And that is down to rats. This is a human-induced problem, and it is down to humans to do something about it."

And they are. This recent bait drop follows a successful trial two years ago, which cleared 10 percent of South Georgia of the invasive rodents. Next year, Martin said, the group plans to return and finish the job, hopefully rendering South Georgia rat-free by 2015.

Sint Eustatius:---The island of Sint Eustatius has initiated an ambitious two-year project to reduce the number of rats on the island. The project has two leaders, Hannah Madden (Caribbean Netherlands Science Institute), who will look into the impact of rats on biodiversity, and Dr. Teresa Leslie (Eastern Caribbean Public Health Foundation), who will investigate the public health threat. Through these combined activities it is the responsibility of these co-investigators to significantly decrease the number of rats on the island and implement a sustainable rat control program.

Rats in Sint Eustatius are increasingly becoming a problem to humans and nature alike. According to Madden, “rats eat almost everything, from flowers and fruits to plants and meat. Not just agricultural produce, but also the native flora and fauna of the island, are impacted. This could very well result in a reduction of the number of different plants and animals found on Statia, which has happened on rat-infested islands elsewhere. A decline in the island’s biodiversity has various negative effects. It affects ecosystem products and services (such as fresh water and food), and indirectly affects livelihoods and income.” She continues by stating how “rats have been documented eating the single-egg clutch of red-billed tropicbirds during the nesting season, and are likely to impact many other vertebrate species on Statia.”

According to Leslie, in addition to being a risk to nature and biodiversity, rats pose a major threat to public health. Rats carry potential diseases which pose a direct risk to human and animal health”. “The bacterial disease leptospirosis, which is often associated with rats, poses a serious threat in the Caribbean and is not adequately documented” says Leslie. Through a collaboration with Ross University School of Veterinarian Medicine in St. Kitts, a component of this work will investigate diseases rats in Statia may be carrying. Leslie believes that “knowing about potential diseases can be used to raise community awareness about the need to reduce the number of rats on the island”.

Both Madden and Leslie agree that community involvement is critical to the success of the program. ”The people of St. Eustatius identify rats as an island problem. However, there is no systematic approach to their control” says Leslie. According to Madden, “in order for this project to be successful, the community must be engaged and understand that they can play a major role in solving our rat problem”.

This two-year, island-wide rodent control project began on February 1. The project is funded by the Netherlands Ministry of Economic Affairs and facilitated through the Caribbean Netherlands Science Institute (CNSI). In 2019, the Public Health Department will continue to implement the rodent control program created by Leslie and Madden to ensure long-term sustainability.

The remote Caribbean island of Redonda, part of Antigua and Barbuda, is home to numerous species of plants and animals found nowhere else on earth. It is also home to invasive black rats and non-native goats that are wiping out the island’s native, rare wildlife, conservationists say.

To help the island’s flora and fauna, the Government of Antigua and Barbuda is now initiating a plan to remove all goats and rats from the island. The Redonda Restoration Program program has been formed by the Antigua & Barbuda Government and the Environmental Awareness Group (EAG) in collaboration with organizations like Fauna & Flora International, British Mountaineering Council, Island Conservation and Wildlife Management International Ltd.