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Utila Spiny-tailed Iguana (Ctenosaura bakeri)

Mohamed bin Zayed Species project number 152511721

Reproductive and dispersal behaviour of the Critically Endangered Utila Spiny-tailed Iguana Ctenosaura bakeri on the island of Utila, Honduras.

Mohamed bin Zayed Species Conservation (Project No. 152511721) - Utila Spiny-tailed Iguana - Awarded $10,000 on February 19, 2016

Introduction

Ctenosaura bakeri is a critically endangered Iguana endemic to the island of Utila. It is known to broadly occur throughout Utila (41km² extent of occurrence), however it likely occupies less than 25% (10 km²) of the island as it is found only within certain habitat areas (Pasachnik et al. 2013). The current population size is not known but estimated to be fewer than 5,000 individuals and is likely declining due to habitat loss and fragmentation, hunting of adults and eggs, invasive species, and predation (Pasachnik et al. 2013). Destruction of habitat is also linked with a reported declining body condition of iguanas in the population (Pasachnik et al. 2012). Ctenosaura bakeri is listed as Critically Endangered by the IUCN since 2004; it is protected under Honduran national law and, since 2010, listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Hunting of the iguana has been banned since 1994 but is rarely enforced.

Background

There is a recorded sex ratio bias within the population, with one female to every 1.7 males, and female numbers are declining (Pasachnik et al. 2012). This is thought to be due to illegal hunting pressure, with gravid females being specifically targeted for consumption (Pasachnik et al. 2012, 2013). While young iguanas and eggs are naturally predated on by, for example, eagles and snakes, feral dogs, cats and rats create additional predator pressures on the species (Pasachnik et al. 2013). Other potential threats include hybridization which has been found to occur between C. bakeri and its widespread congener, the Common Spiny-tailed Iguana C. similis (Pasachnik et al. 2009). While hybridization is not currently thought to be a major threat, increasing habitat degradation and loss will likely have an impact on the genetic health of the C. bakeri population as both species come into increased contact.

To date no studies have been conducted to identify and quantify female migration routes between nesting and breeding sites, and how development of the island and associated habitat losses may impact these routes, and therefore the species. Furthermore, nothing is known about home range, the hatchling success rates, natural sex ratio of hatchlings, and nest characteristics. Population estimates of C. bakeri have varied significantly (Gutsche & Streich, 2009; Pasachnik et al. 2013) highlighting the need for more quantifiably robust work in this area. This information is integral to the effective and active conservation management and protection of the species.

 

 

 Justification

Ctenosaura bakeri and other Ctenosaura populations are under threat from habitat destruction and the effects of overhunting. Little is known of the basic biology of the species (Pasachnik et al. 2012). Many of the natural behaviours and reproductive habits for C. bakeri have not been documented. To date no studies have been carried out on female breeding migration routes, the natural sex ratio of hatchlings as well as wild hatchling success. This information is vital to understanding how the Iguana uses the island.

Currently, there is no species action or recovery plan in place for C. bakeri, though actions such as these were discussed at the IUCN Iguana specialist group meeting held on Utila in 2009. Monitoring, and recovery and management plans require quantifiable ecological data. Demographic data on this species have not been collected in several years; thus an update is needed in addition to filling in the gaps of knowledge. This project will contribute to and inform these priority requirements for the species. Specifically these data will provide a clearer understanding of how C. bakeri utilizes key and threatened habitats on the island, as well as how uncontrolled harvesting may be impacting the status and health of the iguanas, particularly females. This increased ecological understanding can help inform current outreach environmental awareness programs, consequently, the project will contribute directly to the survival of this critically endangered iguana and its habitats.

Objectives

This project aims to:

1) Assess the population size and demography using capture mark recapture methods incorporating an already available dataset of over 700 individuals (Pasachnik et al. 2012);

 2) Determine the reproductive migration and home range of females and males across the island through the use of radio telemetry; and

 3) Collect data health and fitness of the populations, genetics, nest and hatchling ecology, natural sex ratio, clutch size, success rate and biometric measurements.

Methodology

Through late January to September on Utila the Iguanas habitat, reproduction and behaviour will be studied. Iguanas will be captured by hand or noose pole and tagged with radio tags and beaded, PIT tags used or permanent toe clips for identification, depending on the size of the individual (as described by Pasachnik et al. 2012), they will be measured, weighed, probed for sex and photographed.

Once nesting sites have been confirmed using radio tracked individuals, previous records and current local knowledge, they will be monitored daily from March to June, the main nesting period, for new nests. Once found, the location of new nests will be geo-referenced using a GPS.

On emergence, each hatchling will be caught, measurements taken (snout – vent length, tail length, weight) and the sex ratio, clutch size, hatching success, and nest characteristics will also be recorded. The sex ratio of hatchlings will be compared to the adult sex ratio reported in this study and elsewhere (Pasachnik et al. 2012) to understand whether there is any bias in sex ratio from birth.

Additionally, blood and tissue samples for genetic analysis will be taken from approximately 150 mature animals. These samples will be exported and used to analyse the impact of hybridisation in this species giving an update to the 2009 study by Pasachnik et al. 

Project document