2016 Útila Research

A study of the reproductive and dispersal behavior of the Critically Endangered Útila Spiny-tailed Iguana Ctenosaura bakeri on the island of Útila, Honduras

Report submitted by Daisy Maryon, University of South Wales

Ctenosaura bakeri
Largest male C.bakeri found this field season after processing. Photo by Daisy Maryon.

For this project, we investigated the nesting ecology, reproductive and dispersal behavior, and population size of the Útila Spiny-tailed Iguana. We recorded clutch sizes, hatchling success rates, and the sex and biometric measurements of hatchlings at monitored nests. We determined the sex ratio of hatchlings to establish whether lower numbers of females recorded in the population is present from birth or develops post-hatching. We captured, tagged, and radio-tracked individual iguanas to determine movement of adults across the island, gathering information on home ranges and migration routes between breeding and nesting habitats. We employed a capture-mark-recapture method using tagged individuals to provide an estimate of population size. We collected biometric data for tagged iguanas to better understand the body condition and health of the population. There was an urgent need to update previous studies in light of increased degradation and loss of habitat, and poaching of iguanas.


Assessing the population size and demography of the iguana.  A total of 22 transects (50–480 m long) were established in seven areas of Útila. In total, 145 C. bakeri were caught and marked. For each individual, we collected behavioral and habitat data. The same georeferenced data were recorded for any C. similis detected along transects to help identify any potential habitat overlap between the two species, and possible areas for hybridization. DNA samples were collected from all individuals caught for future investigation on the level of possible hybridization.


Iguanas were recorded in mangrove, coastal vegetation, urban habitats, and in some sites overlapping with the Common Spiny-tailed Iguana (Ctenosaura similis). This provides some insight into which areas may be more at risk from land development or hybridization. Some individuals of C. bakeri were found in dive shops on the island and reported inside human habitation. Some survey sites, especially close to town, were frequented by hunters. Through quantifying and monitoring the population, as well as the body condition of individual iguanas, we can compare populations in the potentially more threatened areas to undisturbed sites on the western side of the island and identify areas, and populations, most at risk.

Ctenosaura bakeri
Tagged male C. bakeri basking in White Mangrove. Photo by Daisy Maryon.

Determining the migration and home ranges of iguanas across the island’s habitats.  A total of 37 iguanas were radio-tracked from two locations in Útila. Some were gravid females, which we tracked to their nesting sites. Female iguanas were tracked near urban areas, and were recorded nesting and moving through human habitation to get to nesting sites, and frequently nesting in residential gardens. Iguana’s tags were found in gardens and surrounding walls. We also discovered that some females had double-clutched during the breeding season. Through radio-telemetry, we were able to collect data on home range, habitat preference, activity patterns, and behavior of these individuals. These data provide us with a valuable understanding of the breeding migration routes and an insight into which routes may need more protection in other areas.

Ctenosaura bakeri
Kanahau researcher Tom Brown stuck in mangroves during population surveys, a common hazard! Photo by Daisy Maryon.
Ctenosaura bakeri
The author meets the challenges of tracking mangrove species! Photo by Andrea Albergoni.

Collecting nesting and hatchling biometric and population data.  Data were collected from 35 hatchlings, which were caught opportunistically or processed from two located nests. Egg shells were collected for future genetic analysis to see if an individual’s sex can be determined non-invasively. Habitat surveys (10 m x 10 m plots) were carried out at 10 nest sites by a master’s student from the University of South Wales. Nest sites were located in a range of habitats, which included scrubby vegetation with leaf litter.

Hatchlings were found in a variety of habitats including the center of Útila’s town, further indicating iguanas are nesting in urban areas, and becoming at greater risk to habitat conversion. This highlights the need for more community awareness to protect the iguanas, especially as those individuals in more urban areas may be at greater risk of poaching.

We noted areas of mangrove were for sale for land development, even though this is illegal in Útila. Prime iguana nesting beach areas were also posted for sale. In light of this, the Kanahau Útila Research and Conservation Facility (KURCF) and this project propose that the only way to conserve C. bakeri habitats is by purchasing areas of land for private nature reserves.

Ctenosaura bakeri
Hatchling emerging from nest. Photo by Daisy Maryon.

Additional objectives for the project during this period:

  • The IUCN Red List reassessment for C. bakeri was carried out during the IIF workshop on Roatán and has been submitted for review.
  • It is our intention to discuss the formation of a species action/recovery plan at the next ISG meeting.
  • This project has supported an education program presented to five schools on Útila with the KURCF, the Bay Islands Conservation Association, and the Whale Shark and Oceanic Research Centre. This included lectures on C. bakeri and their habitats, and also engaged the local community by taking school students on population surveys in mangroves on the island.
  • The population survey element of this project will continue next year with the help of the KURCF, with the view of this being sustained as a long-term monitoring project.
  • A general project report will be publicly available on the KURCF website later this year (2016).
  • Over the next four months, we plan to draft scientific manuscripts on habitat selection, particularly regarding nesting sites, home range, and behavior. We feel these will be suitable for consideration in Herpetological Conservation and Biology, the Journal of Herpetology, or Salamandra. While population surveys were carried out during this period, we feel that western side of the island needs to be surveyed more intensively to get a robust global population estimate before publication.
  • A project report in Spanish will be prepared for the Honduran protected areas agency, El Instituto Nacional de Conservación Forestal Áreas Protegidas y Vida Silvestre.
  • This IIF grant has co-supported the successful completion of the fieldwork required for the fulfillment of the author’s Master of Research degree. The thesis will be submitted in January 2017.
  • Collected field data has identified the potential for future research. A Ph.D. by the author is planned to continue to study the conservation ecology and genetics of C. bakeri and the threats it faces.
Ctenosaura bakeri
Nesting habitat of Ctenosaura bakeri using polystyrene as covering for nest. Photo by Daisy Maryon

Future Directions.  We would like to investigate the iguana population on the western side of the island which is largely inaccessible, except by boat. Our objective would be to gather conservation ecology data on the population and nesting sites from this undisturbed area. We will then be able to quantify the total population size and generate population estimates across a gradient of habitat degradation, as well as establish the area of occupancy for C. bakeri on Útila.

We propose to use camera traps to monitor nesting activity on beaches on both the western and eastern sides of the island. Camera traps can also be placed in some residential gardens of the expatriate community who are supportive of the project. This would enable nesting data to be gathered in more urban settings, while also helping to further engage with the local community regarding the conservation of the species. This work would also be supported by using endoscopes to better establish nest sites parameters.

We are also keen to make use of polymerase chain reaction (PCR) analysis for ‘real-time’ DNA sequencing and testing in the field. This has the potential to be a quick and cost-effective approach to support population monitoring and quantification. We plan to apply for IIF funding in the next funding cycle to support these activities.