Galapagos tortoise movement ecology program update

Together with GCT, we were very pleased to release the Tessa book, and conducted a number of local activities with students. Tessa has been a great success already and we are planning to continue our outreach and education sessions in different islands!

The El Paso Zoo and Botanical Gardens supports this important conservation effort to help protect Galapagos giant tortoises in the wild.

Report by the Galapagos Conservation Trust, February, 2023

Last year, our research work remained productive and exciting. Thanks to our various donors and collaborators, we not only continue and expand on-field research improving scientific knowledge of the Galapagos giant tortoise, but we were able to retain our local talent, like it has been the case with Gislayne Mendoza and Cristian Peñafiel. Moreover, the GTMEP have counted with the involvement of committed students and scientists over the years, who have taken over previously initiated research. It is a fact that the GTMEP grows with the professional development of its members.

Photo by Ernesto Bustamante

In 2022, we continued our basic monitoring of tortoise movements on three islands. We currently have 33 adult tagged tortoises and 16 juveniles in Santa Cruz, 9 in Alcedo, and 7 in Española, Additionally, we were able to digitalize and begin to analyze 11 years of tortoise nesting data collected by the GNPD on Santa Cruz Island. Preliminary results suggest that elevation and precipitation affect hatchling success differently by nesting site, hatchling success is negatively correlated with temperature, especially as temperature increases over 25 degrees, and hatchling success is negatively correlated with average precipitation and maximum weekly precipitation in the incubation period.

In June 2022, we started a new research study on relationships between movement ecology and tortoise reproduction. The rationale for the study is to test the hypothesis that migratory females have higher reproductive output than non-migratory females. This gets at the heart of the two major driving forces of our program over the last 12 years; 1. Under what circumstances and by which mechanisms does migration evolve, and 2. How do we better conserve Galapagos tortoises and other migratory species. This study assesses the reproductive output of migratory and non-migratory tortoises by conducting x-rays of female GPS-tagged tortoises from the Cerro Fatal population (Chelonoidis donfaustoi). X-rays allow accurate counts of egg production (Figure 1).

A total of 20 females were monitored with radiographs performed every 21 days during the whole reproductive season. The first preliminary results comparing egg production and number of clutches suggested that migratory females lay more eggs and produce more clutches than non-migratory females. We will repeat this study in summer of 2023 and 2024 to generate a robust sample size and validate conclusions.

The value of long-term movement data is apparent for their role in understanding the roles of climate change, land use change, and invasive species on tortoise ecology. For instance, we are in the final stages of submitting a manuscript on the potentially catastrophic relationship between tortoise migrations and invasive Cuban Cedrela forest. From 140 migratory journeys documented, just 18 involved tortoises entering Cedrela forest; our analysis demonstrates that migrations occur almost exclusively through small, restricted corridors where Cedrela has not yet invaded (Figure 2).

Photo by Ernesto Bustamante

We are also in the final stages of preparing a manuscript on the seasonal relationships between tortoises on Española Island and opuntia cacti. Our data obtained from telemetry and a camera trap show the proximity of tortoises to opuntia, specifically how saddleback tortoises expand and contract their range seasonally around large opuntia trees (Figures 3 & 4). During the dry season, tortoises spend much of their time under opuntia seeking food and water (in the form of occasional fallen pads), and shade. During the wet season, tortoises undertake multi-week foraging trips away from opuntia, to feed and presumably lay eggs. The paper provides new insights into the relationships between habitat features and tortoise ecological requirements.

Two of our PhD students successfully accomplished their projects with outstanding results. Kyana Pike presented her thesis entitled “The interaction between giant tortoises and agriculture in the Galapagos Islands”, where she addressed a detailed understanding of the dynamics impacting tortoise interaction with agriculture in Santa Cruz. The thesis has four main chapters that contribute evidence-based decision support for wildlife managers and conservationists to balance the needs of tortoises in farmland. Working on tortoise health, Dr. Ainoa Nieto Claudin defended her PhD in November entitled “Health assessment of Galapagos giant tortoises from a One Health perspective”. Her PhD thesis is one of few documents written in Spanish compiling tortoise health research.

Photo by RashidCruz

Local students Samara Zeas and Paz Guillén accomplished their undergrad studies by describing, for the first time, Aphanoascella galapagosensis as the main fungal agent involved in the carapace white lesions presented in giant tortoises. This work contributed to a better understanding of the pathogens that are present in Galapagos tortoises and constitutes the first report of this fungus in Galapagos wildlife. This is the first attempt to describe tortoise carapace microbiome, which might be correlated with poor growth and performance of hatchlings.

Three more local students, Karina Ramón, Manuela Burbano, and Miguel Perea, continue their work on tortoise plastic ingestion and carapace microbiome. Their results will be of much importance since this would be the first description of plastic ingestion in any Galapagos terrestrial species.

As in previous years, we conducted a whole range of educational experiential activities together with our local partners, reaching out to approximately 210 local children and teenagers, and 62 foreign students. Activities included field trips to tortoise habitats, telemetry tracking, analysis of feces contents, biodiversity inventories, workshops on threats, games, and interactive lessons (Figure 5). As part of the Galapagos Agreement for Education, we provided advice on biodiversity and tortoises, and delivered training sessions for local teachers within the frame of the Galapagos curriculum contextualization.

Anne Guezou educating students at the lab. Photo by Juan Manuel García, CDF

We also contributed with local and international conferences and presentations, including two talks at the 58th Association for Tropical Biology and Conservation conference in Colombia: “Plastic ingestion in giant tortoises: a novel threat to wildlife conservation in the Galapagos Islands” and “Sharing land with giants: Habitat preferences of Galapagos tortoises on farms”. We organized two formative talks to GNP guide and gave two talks to the Royal European Academy of Doctors, which included four Nobel prize winners (Figure 6).

Cover photo by Juan Manuel García CDF

One Comment Add yours

  1. lollytindol says:

    Hi, Rick, love your info on Galapagos tortoises. I helped open that tour for Tauck years ago and had the wonderful opportunity to work with several naturalist guides on the islands. We snorkled, watched the dolphins lead our ship which accommodated 40 guests, and then enjoyed boarding “pangas” , also called zodiacs, to see stuff up close and personal. All the best to the giants!!!


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