reptiles

A common response among lizards to the approach of a predator is to attempt to avoid detection by moving out of the predator’s view. This may involve moving to the opposite side of a twig or tree trunk, moving into a burrow, or moving into vegetation or other structures (McElroy 2019). Here, I report an unusual behavior to avoid detection in the Aruba Whiptail (Cnemidophorus arubensis), a teiid endemic to the island of Aruba. This behavior involves movement into a shadow in the open, with no further concealment.A common response among lizards to the approach of a predator is to attempt to avoid detection by moving out of the predator’s view. This may involve moving to the opposite side of a twig or tree trunk, moving into a burrow, or moving into vegetation or other structures (McElroy 2019). Here, I report an unusual behavior to avoid detection in the Aruba Whiptail (Cnemidophorus arubensis), a teiid endemic to the island of Aruba. This behavior involves movement into a shadow in the open, with no further concealment.

Dutch below

Likely introduced via the exotic pet industry, boa constrictors have had an island-wide population on Aruba since 2005. The impact of boa constrictors on Aruba has led to the implementation of control measures, including removal of snakes from the wild, but their continued presence highlights the need for continues eradication methods to avoid further unbalancing the island’s delicate ecosystems. 

(Photo credit: Vandy Louw)

The boa constrictor is a non-venomous snake species that is native to South America and the Caribbean islands of Trinidad, Tobago and Isla Margarita. Due to their popularity as exotic pets, these snakes have been introduced to other parts of the world, including Aruba. The first boa constrictor was found on Aruba in 1999, and despite efforts to curb their expansion, an island wide population was established by 2005. Between 1999 and 2016, over 4,520 constrictors were captured and removed from the island, however even with these measures, the local boa population has continued to thrive. These snakes can reach lengths over 4m (14 ft) long and can weigh up to 27 kg (60lbs). Although their coloration can vary, they are typically brown, gray and cream patterned, helping them camouflage within tree canopies. Boas rarely interact with humans but have been known to strike when they are threatened, and although not deadly, their bite can be very painful. 

Generalist Diet 

(Aruban burrowing owl (Athene cunicularia arubensis). Photo credit: Christian König)

Boa constrictors are apex predators, meaning they are at the top of the food chain in their ecosystems. In their native habitats, they play an important role in regulating populations of rodents and other small mammals. However, as an invasive species, their generalist diet means they could be a potential concern for a wide variety of native populations.  A 2021 study investigated the stomach contents of over 500 captured boas from Aruba.  Here, researchers identified over 400 different types of prey, with a nearly even split between mammals, lizards and birds.  In fact, with the exception of the seven different bat species known to inhabit Aruba, almost every other type of vertebrate was observed within the stomach contents evaluated. 

Rapid reproduction 

Boas are of significant concern because they mature quickly (within three years), have a long lifespan (40 years) and produce large litters of offspring (50+) every two years.  Left unchecked, this species is able to rapidly reproduce and outcompete native species. Of particular concern is the impact of these snakes on declining native bird populations including the burrowing owl (Athene cunicularia), Aruban parakeet (Eupsittula pertinax), and crested bobwhite (Colinus cristatus).  In fact, one boa dissected had four burrowing owls in its stomach, which when you consider the native population is estimated at around 200 pairs, is significant.  

Island wide Impact  

(Learning about the invasive boa constrictor. Photo credit: Suzanne Hendrik)

Aruba has already tried a wide variety of control strategies.  Organized bounty programs were found to be ineffective, as boas can be very difficult to track for inexperienced hunters. There was also a pilot effort to lure snakes into traps using live birds and chicken broth, however there was limited success given the boa’s preference for ambush predatory behavior. Other methods which have worked in other places, since as the temporary release of mongoose or the intentional introduction of a targeted disease have been dismissed as ecologically irresponsible. 

Overall, the impact of boa constrictors on the island of Aruba has been significant, highlighting the potential consequences of introducing non-native species to new environments. While these snakes may seem harmless in their natural habitats, their introduction to new ecosystems can have far-reaching and unintended consequences.  This is especially true for small islands already facing unsustainable threats from rapid urban development and climate change. 

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 through the press. This article is part of a series of articles on ‘Invasive Alien Species in the Dutch Caribbean”. 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. 

Waarschijnlijk geïntroduceerd via de exotische huisdierenindustrie, hebben boa constrictors sinds 2005 een eilandwijde populatie op Aruba. De impact van boa constrictors op Aruba heeft geleid tot de implementatie van controlemaatregelen, waaronder het verwijderen van slangen uit het wild, maar hun voortdurende aanwezigheid benadrukt de noodzaak van voortdurende uitroeiingsmethoden om te voorkomen dat de kwetsbare ecosystemen van het eiland verder uit balans taken.

 (Boa constrictor. Foto: Vandy Louw)

De boa constrictor is een niet-giftige slangensoort die inheems is in Zuid-Amerika en de Caribische eilanden Trinidad, Tobago en Isla Margarita. Vanwege hun populariteit als exotische huisdieren zijn deze slangen geïntroduceerd in andere delen van de wereld, waaronder Aruba. De eerste boa constrictor werd in 1999 op Aruba gevonden en ondanks pogingen om hun uitbreiding te beteugelen, was er in 2005 een eilandwijde populatie gevestigd. Tussen 1999 en 2016 werden meer dan 4.520 constrictors gevangen en van het eiland verwijderd, maar zelfs met deze maatregelen is de lokale boapopulatie blijven bloeien. Deze slangen kunnen lengtes bereiken van meer dan 4m en kunnen tot 27kg wegen. Hoewel de kleur kan variëren, hebben ze meestal een bruin, grijs en crème patroon, waardoor ze zich beter kunnen camoufleren in boomtoppen. Boa’s hebben zelden interactie met mensen, maar het is bekend dat ze toeslaan wanneer ze worden bedreigd, en hoewel ze niet dodelijk zijn, kan hun beet erg pijnlijk zijn.

Generalistisch dieet

 (Arubaanse holenuil (Athene cunicularia arubensis). Foto: Christian König)

Boa constrictors zijn toproofdieren, wat betekent dat ze aan de top van de voedselketen in hun ecosystemen staan. In hun oorspronkelijke leefomgeving spelen ze een belangrijke rol bij het reguleren van populaties van knaagdieren en andere kleine zoogdieren. Als een invasieve soort betekent hun generalistische dieet echter dat ze een potentieel gevaar kunnen zijn voor een grote verscheidenheid aan inheemse populaties. Een studie uit 2021 onderzocht de maaginhoud van meer dan 500 gevangen boa’s op Aruba. Hier identificeerden onderzoekers meer dan 400 verschillende soorten prooi, met een bijna gelijke verdeling tussen zoogdieren, hagedissen en vogels. In feite, met uitzondering van de zeven verschillende vleermuissoorten waarvan bekend is dat ze Aruba bewonen, werd bijna elk ander type gewervelde waargenomen in de beoordeelde maaginhoud.

Snelle voortplanting

Boa’s zijn een grote zorg omdat ze snel volwassen worden (binnen drie jaar), een lange levensduur hebben (40 jaar) en elke twee jaar grote nesten nakomelingen produceren (50+). Als dit niet wordt tegen gehouden, kan deze soort zich snel voortplanten en inheemse soorten overtreffen. Van bijzonder belang is de impact van deze slangen op afnemende inheemse vogelpopulaties, waaronder de Arubaanse holenuil (Athene cunicularia), maïsparkiet (Eupsittula pertinax) en kuifbobwhite (Colinus cristatus). In feite had één ontlede boa vier holenuilen in zijn maag, wat aanzienlijk is als je bedenkt dat de inheemse bevolking wordt geschat op ongeveer 200 paren.

Eilandwijde impact

Leren over de invasieve boa constrictor. Foto: Suzanne Hendrik

Aruba heeft al een breed scala aan controlestrategieën uitgeprobeerd. Georganiseerde premieprogramma’s bleken niet effectief te zijn, aangezien boa’s erg moeilijk te volgen kunnen zijn voor onervaren jagers. Er was ook een proefpoging om slangen in vallen te lokken met behulp van levende vogels en kippenbouillon, maar er was beperkt succes gezien de voorkeur van de boa voor roofzuchtig gedrag in een hinderlaag. Methoden die op andere plaatsen hebben gewerkt, zoals de tijdelijke vrijlating van mangoest of de opzettelijke introductie van een gerichte ziekte, zijn afgedaan als ecologisch onverantwoord.

Over het algemeen is de impact van boa constrictors op het eiland Aruba aanzienlijk geweest, wat de mogelijke gevolgen benadrukt van het introduceren van niet-inheemse soorten in nieuwe omgevingen. Hoewel deze slangen in hun natuurlijke leefomgeving misschien onschuldig lijken, kan hun introductie in nieuwe ecosystemen verstrekkende en onbedoelde gevolgen hebben. Dit geldt met name voor kleine eilanden die al te maken hebben met onhoudbare bedreigingen door snelle stedelijke ontwikkeling en klimaatverandering.

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 andere de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en via de pers. Dit artikel maakt deel uit van een serie artikelen over ‘Invasive Alien Species in the Dutch Caribbean’. 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 indirecte gevolgen die voortvloeien uit het publiceren van dit artikel.

Published in BioNews 63

I. Introduction
A. Geography, climate, extended dry periods, tankis and earthen dams, and vegetation Aruba, Curaçao, and Bonaire, together with the Venezuelan islands of Los Monjes, Islas Aves, Los Roques, La Orchila, and La Blanquilla form an archipelago north of the Venezuelan coast. Biogeographically, these islands do not belong to the West Indian region; their flora and fauna are mainly of South American origin. There are many endemic elements in the fauna, largely derived from South American ancestors. This justifies the view that these islands form a small, but distinct, zoogeographical subregion belonging to the South American realm (Wagenaar Hummelinck 1940). The fauna (Wagenaar Hummelinck 1940) and especially the flora (Stoffers 1956) both contain West Indian elements too. Wagenaar Hummelinck makes a distinction between older and newer West Indian fauna. The West Indian elements are especially strong in the flora. Stoffers states the following (about the Dutch Leeward Islands):

Of the species with a more restricted distribution the West-Indian plants (35)
are the most numerous, the South American element being represented by only
22 species. The vegetation of the Leeward group therefore resembles the flora of
the Antilles, rather than the flora of South America, at least from a floristic point of
view. However, physiognomically the vegetation corresponds more to that of the
dry region of northern South America.

Perhaps this area (the Monjes–La Blanquilla archipelago) should be considered an intermediate zone between the West Indies and the South American realm. The Venezuelan islands of Los Monjes, Islas Aves, Los Roques, La Orchila, and La Blanquilla are devoid of amphibians. Of the islands covered in this chapter, Curaçao is the largest with a surface area of 444 km2. Aruba has a surface area of 190 km2 and Bonaire 289 km2 (including Klein Bonaire with 7 km2). Their climate is rather arid compared to most Caribbean islands, with a mean annual rainfall of 409 mm, 557 mm, and 463 mm respectively (Meteorological Service of Netherlands Antilles and Aruba). Aruba is the most arid of the Dutch islands, while the western parts of
Curaçao receive the most rainfall; the mean temperature across the archipelago is about 28°C. The hilly areas receive slightly more rain, and rainfall can be quite variable from year to year. Dry years have only 200–300 mm of rain, while the maximum is about 1,100 m. The driest year on record for Curaçao is 1914, which saw an average of 207.9 mm. Every century there occur several extended periods of drought with practically no rain (van Buurt 2010) (Figs. 10.1–10.3).

Caribbean flora and fauna have always coped with the destructive forces of hurricanes. However, climate change leading to an increase in their frequency and strength, and because many species have declined in abundance due to anthropogenic causes, a better understanding of how hurricanes effect local populations is essential.

The Quill before and after Hurricane Irma. Photo credit: Hannah Madden

2017 Hurricane Season

The 2017 Caribbean hurricane season was the most intense recorded to date. Both Irma and Maria, category-5 hurricanes, closely passed Sint Eustatius and caused major destruction on the island; reported in this Nature Today article. Although immediately after the storms it was clear that trees were heavily affected and mostly defoliated, understanding which species were affected and to what extent requires time for data collection and comparison. Since 2017, several studies have provided pieces of information in order to understand how local populations coped, or not, with the 2017 hurricane season.

Since 2017, researchers found that >90% of all trees were defoliated by more than ¾, and that especially trees at higher elevations (such as on the Quill volcano) were affected more severely. Another study that focused on the Bridled Quail-dove (Geotrygon mystacea), demonstrated that the population declined by 77% in 2019 compared to pre-hurricane levels. A follow-up study in 2021 (not yet published) recorded a further decline to just 125 individuals, and the Bridled Quail-dove will likely be re-assessed by the IUCN.

Reptiles

Focusing on reptile species, a novel study further aids our understanding of the ecosystem-wide impact that the 2017-hurricane season had on Statian biodiversity:

The new study, focusing on the Critically Endangered Lesser Antillean iguana (Iguana delicatissima), shows that its population decreased by at least 20% during 2017. Comparing sighting and survey data from 2017–2018, the authors found a decrease in both the occupancy and population size of the iguana species. Importantly, no recovery was observed in 2019, suggesting that this already small population needs multiple consecutive years without major hurricanes to recover. Interestingly, similar to Statia’s forests, iguanas at higher elevations were found to have been affected more severely.

Letter Antillean Iguana. Photo credit: Philippa King

Importance

Small islands such as Sint Eustatius are home to declining populations of rare and endangered species. In many cases, these isolated populations are unable to migrate between islands and thus populations can only increase in size locally. These new studies highlight the need to improve habitat quality and lower anthropogenic threats to optimize the natural recovery of these species. Ideally, at least for population increase could be aided by a local head-starting project where baby iguanas are nourished in temporary captivity and released once they are larger and more likely to survive.

You can find the full study here entitled “Hurricane-induced population decrease in a Critically Endangered long-lived reptile” using the DCBD link below.

More info in the Dutch Caribbean Biodiversity Database
 

Downloads & links >

Published in BioNews 54

Simple Summary: The illegal pet trade remains an ongoing, substantial threat to wild populations,
especially small insular populations, and can even lead to extinction. Fraudulent activity within the
global reptile trade is known to occur, but its identification through forensic applications depends
on knowledge of diversity within wild populations. In this study, we assessed the geographic origin
of melanistic iguanas (Iguana iguana), which are only found in nations that have never authorized
legal export of live animals. Analysis of genetic data from two pet iguanas in the USA flag these as
originating from Saba or Montserrat, from which no export permits have ever been issued, confirming
their illegal origin. Despite the international trade in I. iguana, in which tens‐ if not hundreds of
thousands of specimens are traded each year, only a handful of individuals have been genetically
assessed. Our work highlights the utility of applying forensic genetic techniques to this trade in
order to track and discourage illegal activity.

Abstract: Lizards within the Iguana iguana species complex are among the most common reptilian
pets, with the widest natural geographic range among iguanids. Deep phylogenetic divergence distinguishes
multiple mitochondrial clades, and several taxonomic changes have recently been proposed.
These small populations, typically island endemics, are threatened by numerous factors, including
the international pet trade. Recent investigations reveal the absence of required CITES permits
for lawful export of animals, providing evidence of ongoing illegal trade. Additional monitoring
of trade in iguanas can be achieved through the application of forensic molecular techniques. In
this study, two captive melanistic iguanas were genotyped for molecular markers for which geographic
distributions of alleles have been established. Mitochondrial sequencing indicates that both
animals carry a haplotype known to originate from the islands of Saba and Montserrat, populations
taxonomically proposed to be Iguana melanoderma. Genotypes at 15 microsatellite loci are equally
consistent with this origin, given the results of a principal component analysis. This first forensic
genetic assessment within the extensive I. iguana pet trade highlights the presence of illegal activity.
The need for additional forensic assessments of pet‐trade iguanas is evident, especially given that
their value is driven by variety and rarity, which is further intensified by recent taxonomic changes.