Female Tortoises in Macedonia Are Walking Off Cliffs Due to Constant Sexual Aggression from Males
Female tortoises are apparently under considerable threat on the island of Golem Grad in North Macedonia, as published in the journal Ecology Letters. During the observations, researchers noted that female tortoises were walking off cliffs, some of which resulted in their deaths. A deeper look into the situation revealed that constant sexual aggression from males was a possible cause behind this step. The evaluation also suggested that females from the island had lower reproduction and survival rates compared to the neighboring mainland population. Researchers believe this could be attributed to their disturbed emotional and physical state due to continuous harassment.
The evaluation was initiated when the team discovered that male Hermann’s tortoises outnumbered females in the area, per the New York Times. There were reportedly regions on the island with 19 males for every one female. To shed light on this imbalance, researchers examined 16 years of data on this particular tortoise population. The results of this pursuit suggested that many factors are responsible for this imbalance, one of which was the behavior of male tortoises towards females. The team also determined that if the situation does not change, then the last female Hermann’s tortoise on the island would die in 2083.
Lead author Dr. Dragan Arsovski and his team believe that males are behaving like this due to competition. In multiple instances, male tortoises were seen mounting over another for a chance with the female, who was buried at the lowest. Such aggressive behavior caused a lot of physical injuries to the females. The team also noted occasions of forced copulations on the island. Males were noted biting the females and piercing their genital opening (cloaca), which protects the female reproductive organs. This action also facilitates damage to such parts. A survey concluded that three-fourths of the Hermann’s tortoise females on the island had injury marks on their reproductive parts.
Along with physical damage, the behavior also hampered the mental state of the female specimens. X-ray examinations of the females revealed that only 15% of the population carried eggs. Most of them had empty abdominal cavities. The harassment may be hurting their reproductive performance. Furthermore, many are also inflicting self-damage to save themselves from the situation, as they are jumping off the cliffs on the island. The phenomenon was observed in both males and females, but in the case of the latter, it was significantly higher and could not be ruled out as an accident.
To understand what causes the cliff exits, researchers conducted an examination, where they initially separated the island tortoises from the males with the help of a fence. There was a cliff exit in the separated area. Island tortoises eventually crawled towards the exit; the mainland females did not choose the pathway even when alone. After sexually aroused males were introduced into the environment, some mainland females were pushed to the exit, while most of the island females voluntarily jumped from the cliff, possibly to avoid the males.
During the examination, GPS devices were attached to a small number of egg-carrying females on the island. One day, the accelerometer data from the devices exhibited abnormal spikes. The team went to the field and found one of the females dead on the beach with a shattered shell. The team speculates that this female committed suicide, as falling off cliffs inflicts shell damage. Hermann’s tortoises live for around 100 years, and such premature deaths could push them towards extinction. “The high density of aggressive males appears to create a vortex of extinction. It’s shocking to witness such a case occurring in nature without human interference like pollution or habitat destruction,” Dr. Jacek Radwan, a professor of evolutionary ecology at the University of Toledo, said, per The Chosun Daily.
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