Published Jan. 26 in Ecology Letters, a new study reports extreme male bias among Hermann’s tortoises on the island of Golem Grad—locally up to 19 males per female. Researchers, led by Dr. Dragan Arsovski, found intense male sexual harassment drives females to flee, sometimes off cliffs, and is associated with reduced reproduction and survival. Based on 16 years of data, models project the last female could perish by 2083, prompting urgent conservation concern.
Female Hermann’s Tortoises Driven Off Cliffs by Male Sexual Harassment, Study Warns
Stock image of three Hermann's tortoisesGetty
A new ecological study published Jan. 26 in Ecology Letters finds that female Hermann’s tortoises on the island of Golem Grad, North Macedonia, are suffering extreme levels of male sexual aggression. Researchers report severely skewed local sex ratios—up to 19 males for every female in some areas—and document cases in which harassed females flee pursuing males and sometimes fall from cliffs, with fatal outcomes.
Key Findings
Drawing on 16 years of field data collected in part by lead author Dr. Dragan Arsovski of the Macedonian Ecological Society, the team shows that intense male harassment is linked to lower reproduction and reduced annual survival among island females compared with a nearby mainland population. Behavioral observations and field notes describe males that pursue single females en masse, and that repeatedly bump, bite (sometimes causing blood loss), mount, and jab fleeing females with a sharp tail tip. Many females were recorded with genital injuries consistent with repeated aggressive encounters.
Stock image of Hermann's tortoisesGetty
“She's literally buried by males,” Dr. Dragan Arsovski said, describing multiple males overwhelming individual females.
The researchers modeled population trajectories and warn that the local population may be trapped in an accelerating decline: based on current trends they project the last female on Golem Grad could die by 2083. Evolutionary ecologist Jeanine Refsnider described the dynamics as an "extinction vortex," noting she had "never heard of anything like that" occurring in a natural, nonhuman-driven context.
Conservation Implications
The study highlights how social and behavioral factors—here, extreme sex-ratio bias combined with relentless sexual coercion—can interact with population structure to produce severe extinction risk for isolated populations. Authors call for continued monitoring and consideration of targeted conservation interventions to assess whether the predicted loss of females can be averted.
Sources
Findings summarized from the paper "Sex Ratio Bias Triggers Demographic Suicide in a Dense Tortoise Population" (Ecology Letters, Jan. 26) and reporting in The New York Times and People.
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