iguana

The Caribbean Netherlands island of Saba is home to a unique but relatively unknown iguana population. Given the many threats faced by islands worldwide, including the Lesser Antilles and Saba, fieldwork was conducted in 2021 in order to bring attention to this unique species and the threats it faces. As on St. Eustatius, the most urgent threats appear to be low survival of hatchlings, limited nesting sites, and the presence of non-native iguanas.

Precise taxonomic status in discussion

Saba black iguana. Photo source: Thijs van den Burg

The iguana population on Saba forms part of a recently described species, Iguana melanoderma. Although there is no doubt about the unique appearance of the iguanas, experts are still deliberating over its exact taxonomic status. Despite this, it is clear that the population requires urgent protection given the number of threats it faces. The biggest concern is the presence of and possible further influx of non-native iguanas from nearby St. Maarten.

Thankfully more iguanas than originally thought

A recent study estimated the iguana population at just 200-300 individuals. This number is worrying and would be extremely concerning for the long-term survival of the population. However, because the data in the aforementioned study were preliminary, additional fieldwork was conducted on Saba in 2021. During this time, 38 transects were surveyed multiple times using distance sampling methodology, which allowed the population to be estimated more accurately. An unexpected positive result of this analysis is that the population is at least ten times larger than originally estimated, in the thousands rather than hundreds.

Saba black iguana. Photo source: Thijs van den Burg

More melanism at higher altitudes?

It is widely believed that black reptile species have evolved this color in order to be able to get warmer faster in colder climates, given that they are cold-blooded. This may also apply to the iguanas on Saba, which boasts the highest mountain in the Kingdom of the Netherlands: Mount Scenery (887m). This high volcano ensures that Saba is often cloudy, which could make it difficult for reptiles to get warm. However, we did not find any relationship between the extent of melanism and the elevation at which iguanas were found. In other words, iguanas that live higher up the volcano are not darker than iguanas at lower elevations.

Is there another explanation for why the iguanas on Saba are black? One hypothesis is that the original iguanas that established on Saba were already black. This is in line with the existence of partially black iguanas in Venezuela, which appear to be closely genetically related to the iguanas on Saba.

Few nest sites or juvenile iguanas

In order for successful reproduction and conservation of an iguana population, good quality nest sites are essential. It is well known that goats can destroy iguana nest sites through overgrazing, which leads to habitat destruction. Furthermore, goats can trample iguana nests and destroy the embryos inside eggs.

On Saba there is an enormous goat population (several thousands) which negatively impacts the island’s vegetation and causes erosion. During fieldwork we searched for iguana nest sites to evaluate their availability, distribution and quality. While this was not the main goal of the research, we were disappointed to find only four nest sites.

Juvenile iguana. Photo source: Thijs van den Burg

Another area of concern was the low number of juvenile iguanas found during fieldwork. Despite finding over 600 individuals, just 2.4% of these were juveniles or hatchlings. While the exact reason for this is unknown, one possible cause could be the feral cat population. Previous research on Saba demonstrated that feral cats exist in the lower altitudes of the island where they hunt for prey, which are exactly the same areas where iguanas prefer to nest. In fact, iguana remains were found in 9% of the cat scats examined.

Unfortunately, the situation for the melanistic iguana on Saba appears to be similar to that of the Lesser Antillean iguana on St. Eustatius, where the presence of cats and goats and an absence of suitable nest sites are well-known issues.

Remaining areas of concern

Despite the larger than expected iguana population on Saba, there are still many causes for concern. Clearly the species needs better protection as well as continued knowledge-building. Pressing concerns for the long-term existence of this species are the presence of free-roaming goats and feral cats, as well as the low number of juveniles and absence of suitable nest sites. However, by far the biggest threat is the presence of non-native iguanas which, though competitive hybridization, can mate with and thereby suppress the native population. During fieldwork, some individuals were found that looked different to the native iguana, and preliminary genetic research has confirmed that these animals were indeed invasive. This situation therefore requires the authorities to take immediate action in order to halt the invasion of non-native iguanas.

More info

For more info, e.g. considering student projects please contact dolfi.debrot@wur.nl and thijs.burg@gmail.com

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 56.

Abstract

The Lesser Antilles, in the Eastern Caribbean, is inhabited by three Iguana species: the Lesser Antillean iguana Iguana delicatissima, which is endemic to the northernmost islands of the Lesser Antilles, the introduced common iguana from South America, Iguana iguana iguana, represented also by the two newly described endemic subspecies Iguana iguana sanctaluciae from Saint Lucia and Iguana iguana insularis from Saint Vincent and the Grenadines, and Grenada, and the introduced Iguana rhinolopha from Central America. Drawing on both morphological and genetic data, this paper describes the Iguana populations from Saba and Montserrat as a new species, Iguana melanoderma. This species is recognized on the basis of the following combination of characteristics: private microsatellite alleles, unique mitochondrial ND4 haplotypes, a distinctive black spot between the eye and tympanum, a dorsal carpet pattern on juveniles and young adults, a darkening of body coloration with aging (except for the anterior part of the snout), a black dewlap, pink on the jowl, the high number of large tubercular nape scales, fewer than ten medium sized–triangular dewlap spikes, high dorsal spikes, and lack of horns on the snout. This new melanistic taxon is threatened by unsustainable harvesting (including for the pet trade) and both competition and hybridization from escaped or released invasive alien iguanas (I. iguana iguana and I. rhinolopha) from South and Central America, respectively. The authors call for action to conserve Iguana melanoderma in Saba and Montserrat and for further research to investigate its relationship to other melanistic iguanas from the Virgin Islands and coastal islands of Venezuela.

Keywords: Conservation Biology, Iguana, Lesser Antilles, microsatellites, mtDNA, new endemic species, phylogeny

A new study by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute highlights the need for a continuation of the rapid response removal campaign to control the invasive green iguana population. Through displacement and hybridization, the green iguana threatens to wipe out the endemic Lesser Antillean Iguanas of St. Eustatius.  

The Lesser Antillean Iguana, , is an IUCN Red List Critically Endangered species, which has disappeared from most of its habitat, including St. Maarten. This species is endemic to St. Eustatius and is the largest native vertebrate on the island. Its main threat comes from displacement by and hybridization with the invasive species green iguana, Iguana iguana.  In fact, St. Eustatius is one of the last three major islands where this species was (until recently) still free from hybridization.  Biological invasions can create several issues which threaten biodiversity, the environment, agriculture, livelihoods, health, and local culture. 

Photo credit: Philippa King

Rapid Response 

In February of 2016, an adult female green iguana was caught in Princess Estates on St. Eustatius. Green iguanas and their hybrid offspring can be most easily distinguished from the native iguana based on their banded tail and the large scale on their cheek (see figure).  It was unknown how long this individual had been on the island and if she had already laid eggs, potentially introducing additional iguanas to the area. In response, the Ministry of Economic Affairs agreed to fund a limited Rapid Response Removal Campaign (RC) on the island.  

During the RC, three visual surveys were conducted throughout key risk areas.  In total, 409.5 hours were spent over 40 days, resulting in a single detection.  This low detection rate suggested that the RC occurred early in the invasion process and highlighted the need to stay vigilant. Luckily, local publicity via newspaper and radio programs led to a number of publicly reported sightings. Among these reports and opportunistic encounters by park management staff, an additional five green iguanas and their hybrids were captured before the campaign ended in January 2017, and an addition eight have been captures since. 

Research 

As part of the RC, a study was conducted by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute (CNSI) to learn more about this invasion. In addition to tracking population data during the surveys, they also worked to identify introduction events, points of entry and likely points of origin.  The harbor of St. Maarten was identified as the source of the most recent 2020 introductions, as this harbor serves as a major inter-island transshipment hub within the Lesser Antilles.  This recent study highlights four apparently distinct green iguana introduction events between 2013 and 2020, one of which was likely intentional and three of which were from incidental stowaways arriving on container ships. 

Photo credit: Dolfi Debrot

Moving Forward 

Luckily even four years after the RC the numbers of green iguanas and their hybrids appears to be limited.  This gives researchers hope that it is not too late to stop the invasion before it heavily interbreeds with and thus effectively wipes out the island’s critically endangered Lesser Antillean iguana.  Research alone will not be enough to control this issue. Investment both in finances and in capacity necessary to prevent introduction and spread of these iguanas will be required.  RCs are significantly lower in cost than full invasive species removal projects, so the early detection and active management provides a unique opportunity for the island to eradicate this threat while still possible and affordable.   

Report your sightings 

If you happen to spot a green iguana while on St. Eustatius, you can report it to the local park authority STENAPA (+599 318 2884) or CNSI (+599 318 2040) as well as on https://dutchcaribbean.observation.org. This is a free website and app which allows local citizens to report sightings of important plants and animals. These tools are available in over 40 languages and can be used by biologists and citizens and tourists alike. Species reports by local communities are invaluable for nature conservation efforts to help increase public awareness and overall species protection.  

Read the full report on the Case Study of a Rapid Response Removal Campaign for St. Eustatius on the Dutch Caribbean Biodiversity Database. 

https://www.dcbd.nl/document/st-eustatius-invasive-alien-green-iguana-ca...

Article published in BioNews 47

Abstract.– Intraspecific diversity is among the most important biological variables, although still poorly understood for most species. Iguana iguana is a Neotropical lizard known from Central and South America, including from numerous Caribbean islands. Despite the presence of native melanistic I. iguana populations in the Lesser Antilles, these have received surprisingly little research attention. Here we assessed population size, distribution, degree of melanism, and additional morphological and natural history characteristics for the melanistic iguanas of Saba, Caribbean Netherlands based on a one-month fieldwork visit. Using Distance sampling from a 38- transect dataset we estimate the population size at 8233 ±2205 iguanas. Iguanas mainly occurred on the southern and eastern sides of the island, between 180-390 m (max altitude 530 m), with highest densities both in residential and certain natural areas. Historically, iguanas were relatively more common at higher altitudes, probably due to more extensive forest clearing for agricultural reasons. No relationship was found between the degree of melanism and elevation, and few animals were completely melanistic. Furthermore, we found that body-ratio data collection through photographs is biased and requires physical measuring instead. Although the population size appears larger than previously surmised, the limited nesting sites and extremely low presence of juvenile and hatchling iguanas (2.4%), is similarly worrying as the situation for I. delicatissima on neighboring St. Eustatius. The island’s feral cat and large goat population are suspected to impact nest site quality, nest success, and hatchling survival. These aspects require urgent future research to guide necessary conservation management.

Locations (lat/lon) of sightings of Iguana recorded in:

• 2015, 191 sightings
• 2016, 89 sightings
• 2017, 114 sightings
• 2018, 70 sightings

No dates or effort (survey time) is recorded.

The Lesser Antillean Iguana (Iguana delicatissima) is endemic to Sint Eustatius as well as other islands of the Lesser Antilles. Since 2010 I. delicatissima is classified as endangered on the IUCN Red List. Iguana delicatissima has various threats for a longer period, but since last year a new threat has presented itself. The Common Green Iguana (Iguana iguana) was found on the island. The presence of the I. iguana is a serious threat for the I. delicatissima due to hybridization and habitat competition. In this study there is researched what the habitat preference is of I. delicatissima and the hybrid. Besides the habitat preference the distribution of the iguanas is mapped. With this information it hopefully will be easier to find the iguanas and STENAPA will be able to save the I. delicatissima from hybridization. Twelve transects were walked all over the island. Also is information obtained from citizens and opportunistic data is used. The exact location, plant species and whether the iguana was found in the sun were documented. To see if iguanas have a significant preference for sunlight a binomial test has been used. A total of 72 I. delicatissima were caught and the data of 7 hybrids was used. Of the 72 I. delicatissima 13 were found on the ground and of the 7 hybrids 5 were found on the ground. Most of the I. delicatissima were found in trees of which is known to be used as food. One of the hybrids was found in a same plant species which also I. delicatissima was found in. There was too little data to compare the hybrids with I. delicatissima. In the sun were significantly (p=0,013) more iguanas found than in the shade. There was a high density of individuals at the Welfare street, Mansionweg and Lodiweg. Most hybrids were found in one square kilometer. Concluding there was no significant difference found in habitat preference between the I. delicatissima and the hybrids. There were significantly more iguanas found in the sun compared to the shade. Iguana delicatissima was found widely spread over the island while the hybrids were found within one square kilometer. It is advised to keep documenting the plants the hybrids are found in to be able to say something about the habitat preference. Also it is recommended to place camera traps at nests in the area were hybrids have been found. This way you know if the juveniles are I. delicatissima or hybrids and if the problem is increasing or decreasing.

[Student report]

Het aantal genetisch zuivere Antilliaanse leguanen is aan het verminderen. Het belang om de Antilliaanse leguaan op St. Eustatius zuiver te houden, wordt zeer groot geacht. Daarom dienen oplossingen te worden geformuleerd om beperkende bedreigingen te reduceren. Om deze oplossingen te formuleren diende het individuele leefgebied van de Antilliaanse leguaan onderzocht te worden. Tevens moest er meer bekend worden over de bereidheid en het verantwoordelijkheidsgevoel van de bevolking om een bijdrage te leveren aan dergelijke oplossingen. Door dit onderzoek zijn oplossingen om de genetisch zuivere populatiedichtheid van de Antilliaanse leguaan op St. Eustatius te vergroten opgesteld.

Ten eerste is onderzocht wat het individuele leefgebied van de leguaan is, ook wel de home range genoemd. Hier komt een gemiddelde van 167,5m² uit voor één locatie en enkel vrouwelijke dieren. Hierbij bestaat een spreiding van 48,5m² en is slechts 1% van het eiland onderzocht.

Vervolgens is het verantwoordelijkheidsgevoel van de bevolking op St. Eustatius jegens Antilliaanse leguanen in hun tuinen onderzocht middels een enquête. Hieruit komt een gemiddeld verantwoordelijkheidsgevoel van 8,11/10,00. De spreiding van deze uitkomst is 2,18 en antwoorden liggen tussen 3 en 10. Tevens is de bevolking met een gemiddelde van 7,20/10,00 bereid mee te helpen aan oplossingen die de populatie Antilliaanse leguanen op het eiland moeten vergroten. Antwoorden hierbij lagen niet lager dan een 5 en de spreiding van de antwoorden kwam uit op 1,53.

De uitkomsten van de enquête zijn gekoppeld aan oplossingen om bedreigingen te reduceren. Hieruit is geconcludeerd dat de meeste middelen en materialen die beschikbaar zijn voor oplossingen die betrekking hebben op de bevolking moeten worden ingezet om het bewustzijn van familie en vrienden van de bevolking op St. Eustatius te vergroten.

De resultaten van het gehele onderzoek kunnen niet als betrouwbaar worden beschouwd. Voor een betrouwbare home range dient op 90 andere locaties onderzoek uitgevoerd te worden. Voor een betrouwbaar resultaat van het verantwoordelijkheidsgevoel en de bereidbaarheid van de bevolking dienen in totaal 344 inwoners bevraagd te worden.

Er wordt aanbevolen om vervolgonderzoek te doen naar de home range van de Antilliaanse leguaan op andere locaties op het eiland. Tevens is het goed om een planning te maken waarin bedachte oplossingen kunnen worden gesorteerd op mate van belang en toepasbaarheid. Ten slotte zal STENAPA op een efficiënte manier moeten samenwerken met de bevolking en andere eilanden en organisaties om met elkaar het grootst mogelijke resultaat te behalen.

[Student report]

The purpose of this Position Statement is to highlight the pest status that non-native iguanas can attain when introduced to tropical and sub-tropical regions outside their native range, and to emphasize the devastating environmental and economic impacts they can cause.

Common Green Iguanas (Iguana iguana) and, more recently, Spiny-tailed Iguanas (Ctenosaura similis and C. pectinata) (Fig. 1) have been moved around the world, primarily for the pet trade. The intentional and unintentional release of iguanas has led to the establishment of uncontrolled invasive populations in more than 19 countries, with subtropical and tropical islands being most vulnerable (Table 1). To date, no country has been able to eradicate these species once a breeding population has become established.

Invasive iguanas can exhibit explosive population growth and reach staggering densities. On the small island of Grand Cayman, Green Iguanas have increased from a few individuals to hundreds- of-thousands within a decade. Invasive iguanas are causing multimillion-dollar impacts on infrastructure, agriculture, tourism, long-term food security, and biodiversity. For example, invasive Green Iguanas are a known airport safety hazard in Florida, Puerto Rico, and The Bahamas. They are also known to short-circuit power lines in cities, and their burrows have caused road collapses and coastal erosion (Fig. 2). Invasive iguanas can cause severe agricultural damage and defoliate native and ornamental plants (Fig. 3). Spiny-tailed Iguanas are a proven nuisance in Gasparilla Island, Florida, defoliating native plants and causing thousands of dollars in damages to homes and landscaping. In places where native and non-native iguanas co-occur, the survival of the natives is threatened through competition for food and space. In addition, hybridization with Green Iguanas is now the main threat to the survival of Lesser Antillean Iguanas (Iguana delicatissima) (Fig. 4).

We thus make the following tiered recommendations, which apply to all countries with tropical or sub-tropical regions, and especially islands:

For countries where non-native iguanas are not present: Develop and enforce country-specific regulations to ban importation and prevent the accidental introduction of non-native iguanas.

For countries where non-native iguanas are present in captivity, but have not been detected in the wild: Implement education programs focused on responsible pet ownership, encourage pet sterilization, ban the release of iguanas into the wild, and provide a sanctioned repository for unwanted captive iguanas.

For countries where non-native iguanas have been recently detected in the wild, but have yet to establish breeding populations: Immediately implement well-coordinated and resourced action plans to humanely remove all non-native iguanas before eradication becomes unfeasible (see AVMA guidelines: https://www.avma.org/KB/Policies/Pages/Euthanasia-Guidelines.aspx)

For countries with established breeding populations of non-native invasive iguanas in the wild:

Humanely eradicate existing populations where possible; if eradication is unsuccessful, implement continual management actions to control population growth and prevent further expansion. 

While translating the Dutch version of "de Amfibieen en Reptielen van Aruba, Curaçao en Bonaire" into English, I was forced to go through the entire text one more time, line by line. Thus it was inevitable that I ended up editing the text somewhat and adding to it as well. Since an English manuscript was now available, several people who had not been consulted previously could now give their comments, which have been incorporated in the English version. Thus the English translation is not a literal transcription of the Dutch version, although the differences between both versions are relatively minor. The islands of Aruba, Curaçao and Bonaire form part of a larger archipelago of islands along the Venezuelan coast. This archipelago includes all the islands from Los Monjes in the West to La Blanquilla in the East. The herpetofauna of the islands of Aruba, Curaçao and Bonaire should be viewed from this somewhat larger perspective. For this reason there are many references to the Venezuelan islands. Faunistic zones often transcend national borders. In this respect I have followed wagenaar hummelinck who in 1940 published the first general treatise of the herperofauna of this archipelago. My field guide is in large part based on this early work of wagenaar hummelinck (†).

This field guide is certainly not intended as a taxonomic work. Most guide books use slightly different classifications, sometimes all these differences can be quite exasperating. The latest classification is not necessarily the best, and some of the newer ideas have not gained general acceptance. In this English version the sub-species Leptodeira annulata bakeri and Crotalus durissus unicolor from the Dutch edition have been upgraded to full species status, in accordance with the prevailing taxonomic trends. I have simply tried to follow what seemed "the roads most traveled" and in many cases have indicated that other classifications also exist. In doing this I have certainly developed my own preferences, often siding with the "lumpers'', sometimes with the "splitters". I fully realize however that I do not have the expertise to make these kinds of taxonomic judgments, which are better left to others. It is however important to convey to the general public the idea that taxonomy has a subjective element and that taxonomy is not a static structure, but something that can change on the basis of new evidence or new interpretations. The field guide is also intended as a review summarizing available information on the herpetofauna of these islands. Local information on customs, beliefs and origins of local names has been included. The list of literature, cites many general works but is also intended to serve as a bibliography of the herpetofauna of the islands of Aruba, Curaçao and Bonaire. The sea turtles have not been included. In 1995 I published "De Schildpadden van Curaçao en Bonaire" (The turtles of Curaçao and Bonaire). This book was primarily intended for local use, one of its primary aims was to generate support for sea turtle protection. Since many books on sea turtles in the region already exist, there is no special need to translate this book into English.

Author's note, November 2017: This guide is somewhat outdated; some scientific names have changed, new invasive species have established themselves, at least on Curaçao, and of course new literature has appeared. Actually, a new edition is needed.

Curaçao and Bonaire form part of the Netherlands Antilles, while Aruba has a “status aparte” within the Kingdom of the Netherlands. All three islands are relatively arid compared to a typical Caribbean island, with mean annual rainfall of 409-553 mm, and experience several periods of drought lasting two or more years each century. A short history of the islands is given, and protected areas are described. The laws and regulations protecting amphibians and reptiles are complex, with general laws originating from the Kingdom of the Netherlands participation in international conventions (such as CITES) together with supplemental laws of the Netherlands Antilles and individual islands. Sea turtles are generally well protected, although their nesting beaches would be vulnerable to a rise in sea level. Among the terrestrial herpetofauna, only the Aruba Island rattlesnake (Crotalus unicolor) is on the IUCN Red List, being Critically Endangered. The status of this species and others of particular interest is described. The Curaçao Island snake (Liophis triscalis) should probably be included as Vulnerable or even Endangered, though there is insufficient information at present. Iguana iguana populations on the different islands, and the Curaçao whiptail (Cnemidophorus murinus murinus) on Klein Curaçao, are distinctive and significant for conservation. An overview is given of introduced amphibians and reptiles and their possible effects on the native fauna. The arid climate of the islands may hinder the establishment of invasive species, which are often not able to survive in the bush and thus reduces their impact on native species.