Pinzón Island Giant Tortoise Population Survey: Part 2

December 18, 2014

 

By guest author Dr. James Gibbs of the State University of New York’s College of Environmental Science and Forestry (SUNY-ESF).

 

Pinzon team sharpening machetesIt’s our third day on Pinzón Island and we are huddled beneath a muyuyo tree taking a break from the intense sun. We are grubby, our clothes tattered by thorns and stained by the abundant Croton bushes, our bodies burnt by the intense equatorial sun. Our boots, so easily destroyed by the lava, are held together with duct tape and extra stitching. Yet everyone remains cheerful.

It never ceases to amaze me the cheerfulness of the Galapagos National Park rangers. Much of the banter focuses on the islands; their trails and place names — the best GPS in the world does not serve as well as shared, accumulated knowledge. Amid the happy chatter I hear the constant loud “chings” of files being rasped down the blades of our machetes to sharpen them, an essential tool for maneuvering through the thorny vegetation that defines Pinzón.

A tortoise resting under a nearby bush looks at us askance. I wonder what the tortoises think of all these ephemeral invaders. Normally the only sounds on Pinzón are the wind through the branches, an occasional bird song, the distant pounding of the sea against Pinzon’s daunting cliffs, and the occasional bang of a tortoise carapace against lava. Our constant chatter changes that.


A male tortoise at La Central

We began each day on Pinzón climbing the outer slope from our shore camp up to a large, distinctive cactus, where we’d gather to review the day’s plan. Then we’d depart in pairs to our respective destinations, guided by a map and a GPS, to search for tortoises. We’d inject an identification chip into the left hind leg of each tortoise encountered, measure its length, determine its sex and age group, and finally mark it with paint. A few days later we’d return to the same area for a second search. The ratio of tortoises with paint that are re-encountered to those without paint (unseen on the first pass) enables us to estimate population size.

On one excursion with my work partner, Francisco, we crossed the island and descended into the southern nesting zone, a steep slope that terminates at the top of a cliff some 150 m above the crashing waves. Tortoise nests are easy to identify once you develop the knack. They present a slightly raised mound of soil mixed with tortoise dung, then hardened by the heat of the sun. Tapping the soil cap produces a resonating hollow “tock” sound. Francisco and I were surprised to find one nest so fresh the soil was still pliable and sticky. Although we tracked the female that must have nested within the hour, we were unable to find her.

As we hiked out of the nesting zone, we found an amazingly old tortoise. Her luminous shell, with the underlying bone shining through the remains of the darker keratin layer, had the most intricate patterning I’d ever seen. Perhaps over 150 years old, she had lived decades in a small territory on Pinzón, making the trek to the nesting zone to lay her eggs in the red soil year after year, dry season after wet season — a survivor of the dark times for tortoises on Pinzón.

The plastron and carapace of a very old female tortoise on Pinzon

When we reached the Central Valley, a large flat area with abundant soil and cactus, we were greeted by a large group of tortoises. Francisco explained that two years before, during the rat eradication campaign, tortoises were regularly fed cactus pads there to divert their attention away from eating rat bait. Two years is not much time for tortoises; they still gathered with expectant looks whenever humans approached.

During our treks around Pinzón, the team also found many young hatchlings, a truly exciting find as they are the first hatchlings to survive on Pinzón in more than a century. Once black rats were introduced to Pinzón in the late 1800s, they preyed on 100 percent of tortoise hatchlings. This new bunch of “little guys” is one of the important results of the rat eradication campaign, tangible proof that with dedication, hard work, support, and heart, conservation efforts can effect positive change.

Young Pinzon hatchling

By the end of our trip, the team had encountered over 300 tortoises, resulting in an overall population estimate well over 500, a near tripling of the population from the 100-200 very old individuals encountered on Pinzón when the Galapagos National Park was established in 1959. This welcome change, after centuries of exploitation, is a direct result of the successful captive rearing and repatriation program and now the elimination of the rats.

Vermilion flycatcher on PinzonThere is of course more on Pinzón than tortoises, including an abundance of vermilion flycatchers, a species that is disappearing on the human-inhabited islands of Galapagos. It was a joy to watch them flitting about, searching for insects, and taking dust baths — a beautiful flash of intense color in an otherwise drab landscape. Francisco’s vermilion-colored, long-sleeved cotton shirt constantly attracted the males. They’d alight on a nearby branch and gawk in seeming disbelief at Francisco’s red arms.

Broken jug from pirate or whaler daysAfter a productive if physically challenging trip, we teetered our way back down the uneven lava one last time. Along the way we discovered a remarkable trove of broken glass bottles and clay jugs — clearly from the era of pirates or whalers. A few of the oldest surviving tortoises we’d encountered may have even watched whalers come and go, taking with them thousands of their fellow tortoises. But this lot of humans — park rangers and scientists — are different. Although we prick, poke, paint, measure and generally bother the tortoises, we take only data. The results of our week on Pinzón show an island in recovery, a growing tortoise population, and provide confirmation of the good work of the Galapagos National Park Service and its many collaborators. 

 

Dr. James Gibbs is Professor of Vertebrate Conservation Biology and Associate Chair of the Department of Environmental and Forest Biology at the State University of New York (SUNY-ESF). He has partnered with Galapagos Conservancy for many years in efforts to restore giant tortoise populations in Galapagos through the Giant Tortoise Restoration Initiative.  

Read Part 1, Preparing for the Pinzón Island Giant Tortoise Population Survey.

 

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  8. Jeanine @ sixtimemommy.com on

    How amazing! I truly enjoy reading this story and am so happy to hear of the discovery of more tortoises!

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