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The high frequency of same-sex sexual behaviors (SSB) in free-ranging animals is an evolutionary puzzle because fitness benefits are often unclear in an evolutionary context. Moreover, the physiological and genetic underpinnings of SSB remain unclear. We exploited an extraordinary natural experiment to examine the impact of environmental factors (local sex ratio [SR]) and testosterone (T) levels on SSB in a dense population of Hermann's tortoises monitored for 7 years. Under the combination of high density and extremely skewed SR (~50 females, >1000 males), males courted and mounted other males more frequently than females. They even exhibited extravagant sexual behaviors, attempting to copulate with dead conspecifics, empty shells, and stones. T levels remained within the species' normal range of variation. SSB was not observed in other populations where SR is not, or less skewed, and where density is lower. This study reports the first natural example of a "prison effect," whereby a high population density combined with female deprivation triggered SSB as a mere outlet of sexual stimulation. More generally, it supports the hypothesis that SSB can be a nonadaptive consequence of unusual proximate factors rather than reflecting physiological disorders.

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Delayed maturity and high survival rates of immatures and adults characterize long‐lived species’ life histories. Understanding how these traits interact in stochastic environments is essential to understand early life in long‐lived species and to assist conservation planning. Unfortunately, available information of demographic traits in immatures are often fragmentary and the logistical difficulties of capturing and recapturing this cohort leave little room for improvement. Published immature chelonian survival estimates vary broadly, are often not age‐specific, and lack precision. In an attempt to overcome this issue, we developed a novel modelling approach based on Capture‐Recapture data to obtain robust age‐specific survival probabilities in two chelonian species (the freshwater European pond turtle, Emys orbicularis, and the terrestrial Hermann's tortoise, Testudo hermanni). More specifically, we show that implementing a linear relationship between survival probabilities and age does not distort survival estimates and improves precision. Both species display a progressive increase in survival with age, reaching a plateau at the ages of four to five. As maturity occurs later in both species (8–12 years‐old), the survival plateau might be governed by the final hardening of the carapace, which brings obvious survival benefits. Taking advantage of the flexibility of multievent models we encourage a systematic field approach even when very large samples from immatures cannot be amassed. Only so can demographic traits in chelonians, and more generally in long‐lived species, be properly explored.