A recent study published in the scientific journal Ecology Letters documents an extreme behavior in the Hermann’s tortoises (Testudo hermanni) on the island of Golem Grad, in the Great Prespa Lake, North Macedonia.
Researchers observed that females voluntarily throw themselves off cliffs to escape the constant sexual harassment from males, a phenomenon described as “demographic suicide”.
Sex imbalance and reproductive pressure
The island’s population is around 1,000 specimens, but in some areas, there are up to 19 males per female. This imbalance creates extreme reproductive pressure:
- Several females are simultaneously pursued by numerous males.
- Mating attempts are marked by violence: ramming, bites that cause bleeding, and stabs with the sharp tail.
- Up to three-quarters of the females have injuries in the genital area.
Ecologist Dragan Arsovski, from the Macedonian Ecological Society, explained that females “literally get buried by males,” leading them to seek a desperate escape route.
Experimental evidence
To reinforce field observations, researchers conducted additional experiments:
- When placing Golem Grad females in front of simulated cliffs, they voluntarily launched themselves.
- In contrast, females from neighboring mainland populations did not show this behavior.
- Harassed females reproduce less and have lower annual survival rates compared to mainland ones.
Hermann’s tortoises in Macedonia face an extreme population imbalance.
Risk of extinction and origin of the imbalance
Ecologist Jeanine Refsnider, from the University of Toledo, stated that male sexual aggression “seems to be causing a extinction vortex for the females.” According to projections, the last large female of Golem Grad could die in 2083, marking the collapse of the island population.
The origin of the extreme sex imbalance remains uncertain:
- One hypothesis suggests a random fluctuation, as there are slightly more females than males on the mainland.
- Another proposes an initial human introduction with unequal proportions, supported by numbers engraved on the shells of some veteran males.
Biology of the species
Hermann’s tortoises can live up to 100 years in favorable conditions, but for many females of Golem Grad, that horizon seems unattainable. The species, distributed in southern Europe, also faces external threats such as habitat loss and climate change.
The case of Golem Grad reveals how an extreme population imbalance can trigger unprecedented and lethal behaviors in wildlife. The phenomenon of females throwing themselves off cliffs is a warning sign about the fragility of island ecosystems and the need to further investigate the causes of this demographic collapse.