Since 2007, representatives from MES, the Faculty of Biology in Belgrade, and the Centre of Biological Studies of Chizé, part of the French National Centre for Scientific Research (CNRS), have been conducting population studies on three reptile species on the island of Golem Grad and in the village of Konjsko: the Hermann’s tortoise, the dice snake, and the nose-horned viper. These studies have described numerous ecological and evolutionary phenomena that help us better understand these animals and, in turn, protect the incredible natural heritage of Golem Grad Island. Students and volunteers from around the world have taken part in this research.
For more information and opportunities to get involved, contact Dragan Arsovski at arsovski@mes.org.mk.
Dice snake with its favorite prey – the Prespa bleak
The lack of fishing regulation around the lake has led to the mass drowning of these animals in nets entangling their favorite prey – the Prespa bleak. Numerous nets are set almost every night around this strictly protected area of the Galicica National Park. In just one instance of retrieving a single net, we managed to pull out over 40 drowned individuals.
Unfortunately, the population of dice snakes (one of only two aquatic snake species in North Macedonia), which gave Golem Grad its famous nickname “Snake Island” due to their remarkable numbers, has been in steep decline over the past decade.
Numerous nets are set almost every night around this strictly protected area of the Galicica National Park. In just one instance of retrieving a single net, we managed to pull out over 40 drowned individuals. Multiply that number by the nights that such nets are set and the number of possible nets around the island’s shoreline, and the result is staggering figures that explain the current absence of these snakes along the island’s coast. Dice snakes are predators of fish, but at the same time, they are prey for many birds and mammals. The collapse of this population is triggering changes across a large part of Golem Grad’s food chain.
The much more secretive and better-camouflaged horned viper (one of the three venomous snake species in North Macedonia) is, for now, in good condition on the island. With a preliminary estimate of around 80 individuals per hectare of island surface, this could easily qualify as the densest population of this species in the world. In the absence of rodents, these vipers feed on lizards, small snakes, and centipedes, and researchers believe that this diet is likely the reason behind the dwarf form of this snake on the island (with a maximum length of around 50 cm).
Horned viper camouflaged in its natural habitat on Golem Grad
Collecting data from a female horned viper
Hermann’s tortoise on the beach in the village of Konjsko
The population of Hermann’s tortoises (one of the two terrestrial tortoise species in North Macedonia) on Golem Grad is not only the densest but also the most unique population of this species in the world.
An extremely skewed sex ratio (17 males to one female) has led to unique occurrences of sexual behavior and selection. Specifically, the males’ aggressive courtship, which in balanced sex ratios stimulates population growth, on Golem Grad has resulted in a dire situation for the few females. Caught in a relentless pursuit, females have developed various strategies to avoid males—including, astonishingly, leaping off the island’s high cliffs. This unsustainable situation will inevitably lead to the extinction of this population.
To the (small) benefit of the females, males—lacking access to mates—have begun directing their sexual energy toward the closest thing resembling a female tortoise: other males. Golem Grad is the first place where systematic homosexual behavior has been documented in tortoises, offering an extraordinary opportunity to study this phenomenon in a very different class of animals (while homosexual behavior is observed in many birds and mammals, it has not been recorded in reptiles until now).
These scientific studies have so far revealed several ecological and evolutionary phenomena described in numerous international scientific publications, including four doctoral dissertations and many bachelor’s and master’s theses. Much more can be read in the following publications:
The Macedonian Ecological Society (MES) is a civil society organization actively working in the areas of ecology and environmental protection.