Tortoise predation by crows: what role does the scrub play?

    The predation of baby tortoises and juveniles by the raven could constitute a threat to the conservation of the chelonian in anthropic habitats of North Africa with little scrub cover


    La night tortoise (Tortoise) It is a species of land tortoise that is widely distributed in North Africa and reaches southern Spain, where we have three isolated populations (Almería-Murcia, Huelva and Balerares). Unfortunately, this chelonian is listed as Vulnerable internationally, so it is very necessary to know its threat factors in order to establish adequate strategies for its conservation.

    The Moorish Tortoise (Tortoise) is a species of tortoise listed as Vulnerable worldwide. This photo shows a one-year-old juvenile (Photo: Amalia Segura).

    In general, turtle populations are characterized by having a high survival rate of adult individuals and low recruitment rates, due to the fact that hatchlings and juveniles are especially vulnerable when faced with, for example, adverse weather conditions, low food availability, or predation.

    In the case of the black tortoise, whose habitat is characterized by semi-arid natural spaces, the few studies available have estimated mortality rates of up to 95% in individuals that have not yet reached reproductive age. However, the knowledge we have of this species at early ages is very limited due to its low detectability.

    The shells of the hatchlings and juveniles of the nightshade tortoise are not sufficiently hardened, so predation could be one of the main causes of early mortality, especially in anthropic environments that favor the abundance of certain opportunistic predators. In relation to this, habitat structure could be determinant of predation risk, since abundant vegetation cover could favor the camouflage of small turtles, making it difficult for predators to detect them.

    These were the hypotheses raised by a group of scientists from the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), who has studied four populations of nightshade tortoise in the Maamora Forest, in northern Morocco.

    This area presents two ideal peculiarities for the development of this work: on the one hand, it is one of the areas in which the highest densities of blackberry tortoise to date; and on the other, it has a growing population of great raven (Corvus corax), whose opportunistic character is favored by the anthropization of the environment.

    The abundance of great raven (Corvus corax) is favored by anthropogenic alterations in the Maamora Forest, where it has increased constantly for several decades (Photo: Amalia Segura).

    The study reveals that, indeed, the raven exerts a significant predatory pressure on the young specimens of the Moorish tortoise, especially on those whose carapace measures between 40 and 70 mm. However, this pressure depends closely on the vegetation cover provided by the scrub.

    Thus, in areas with sparse vegetation cover, the predatory pressure of crows on young black-backed tortoises was strong enough to alter population structure. This fact is especially striking if we compare it with what happens with the Spanish populations of the Moorish tortoise, since in the latter the impact of predation by the crow seems negligible.

    The crows pierce the shells of the small turtles with their beaks and extract their bodies to eat them (Photos: Amalia Segura).

    On the other hand, the results of this study show that the cases of predation were practically anecdotal in the populations of the Moorish tortoise whose habitats had abundant scrub cover, or at least abundant enough to make it difficult for corvids to detect the small turtles.

    This scientific work provides valuable information about the predation of the night tortoise during a critical phase of its life. Besides, warning of possible repercussions for the conservation of this species if the raven populations continue with the growth trend observed to date. In fact, the predation exercised by the crow on another species of land tortoise such as the desert tortoise (Gopherus agassizii) is considered as one of the most important causes of its decline.

    The scientific publication of this research is available at: