Shrewd shrikes and spiny shrubs: a calamity for hatchling Moorish tortoises (Testudo graeca graeca) (original) (raw)
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Scientific Reports
The predation of young tortoise is considered a major cause of mortality for many tortoise species. The predation by common ravens has been identified as being responsible for significant decreases in tortoise populations. Mediterranean spur-thighed tortoise hatchlings and juveniles in Maamora forest (Morocco) were studied in order to describe the size/age class predation of common ravens on young tortoises and infer the drivers of predation risk and population abundance. The results showed a high level of predation on young tortoises (<75 mm carapace length) attributed to ravens in areas with low vegetation cover, representing 100% of the cases of mortality (n = 147), but it was moderate in covered areas (n = 19), representing 12-27%. The population structure of living juveniles differed significantly between covered and uncovered areas, thus suggesting that raven predation might modify juvenile population structure. Finally, N-mixture models showed a positive relationship between (i) bare cover and tortoise detectability that is only evidenced when the plot is far from a perch and (ii) population abundance and shrub species-richness, being higher in uncovered areas. Our results improve the knowledge on predation and survival on this critical stage in life, which is crucial for the conservation of the Mediterranean spur-thighed tortoise. Tortoise populations are characterised by high adult survival and low recruitment rates, which probably influence their demographic dynamics 1. The lack of reliable information on recruitment complicates evaluations of the real importance of young individuals as regards population demography 2. In this respect, threats that limit recruitment bouts may have an important regulatory effect on population dynamics 3 , especially when these threats continue over long periods of time (e.g. 4). Hatchlings and juveniles are more vulnerable than adults owing to their smaller size and higher susceptibility to environmental conditions, such as the temperature or rain, which affect their physiology, but also to vegetation cover, which influences thermoregulation, the availability of food and the risk of predation 3,5,6. Indeed, the low temperature and high rains of winter 2,7 and the high temperature of summer 8,9 are considered some of the most common causes of mortality in hatchlings. The predation of young tortoises-their shell is soft or not sufficiently solid to protect them from predators-by mammals 7,10,11 and birds 12-14 is also considered a major cause of mortality in many tortoise species, which was particularly studied in North America 7,10,12,15,16. The common raven Corvus corax is considered to be one of the most relevant predators of tortoises and is responsible for 70-91% of the mortality of desert tortoises Gopherus agassizii 4,13,17. Both single individuals and breeding pairs have been identified as responsible for significant decreases in tortoise populations, also in addition to modifying population structure by affecting juvenile size/age classes. 12,18,19 Indeed, its high numbers and opportunistic feeding habits have severe impacts on its target prey, whose population size may be reduced without affecting the condition of the predator, which will switch to another prey when this resource becomes scarce (e.g. 4). But the prey species has mechanisms by which to reduce predation. Vegetation cover has been documented as a key determinant as regards reducing young tortoises' detectability, since it facilitates their camouflage 20. Crypsis has anti-predatory benefits, and refuge areas, such as those areas dominated by vegetation cover, may reduce the risk of predation. It has also been documented that ravens' predation on tortoises differs
2021
The endangered Moorish tortoise Testudo graeca is the unique terrestrial chelonian species in North-west Africa. In west-central Morocco, the endemic subspecies, the Souss valley tortoise T. g. soussensis, occupies semi-arid to arid low-quality habitats, and is subject to serious threats. A long-term mark-recapture programme from 2001 to 2012 allowed estimating population size and structure, sex ratio, and survivorship in one of the well-known populations in a degraded and overgrazed arid steppe-land of west-central Morocco. Spring population size considerably decreased to more than half in less than 10 years, with a mean density lower than 3 ind.ha-1 in 2012 compared to its last known density estimat-ed in 2003. In spring 2012, the population structure exhibited an unbalanced male-biased sex ratio (61:39) and a scarcity of juveniles (<5%). We identified five major conservation problems in the study area: (i) habitat destruction and overgrazing; (ii) over-collecting of tortoises ...
Journal of entomology and zoology studies, 2017
We study the activity patterns of a population of the spur-thighed tortoises Testudo graeca occurring in an enclosed area of 30 ha in the National Park of El Kala (northeastern Algeria) with the aim of exploring the variation in daily and seasonal activity of males, females and juveniles from March, 2004 to March, 2005. Our results show that the species displays a unimodal daily activity pattern during spring, with the highest activity during the mornings (81.55 % of active tortoise are seen between 10:00 h and 14:00 h).In summer the daily activity pattern of tortoises is lower and shows a bimodal distribution (22.22 % of active tortoises are seen early in morning between 09:00 h and 10:00 h and 41.67 % are seen later between 16:00h and 18:00 h). No differences were found between the daily activity of males and females. The monitoring of the activity during 7 months revealed that tortoises are most active in March with 2.44 tortoises/hour of search. Later, the activity decreases wit...
Food choice of an Algerian population of the spur‐thighed tortoise, Testudo graeca
African Journal of Herpetology, 2008
The diet of an Algerian population of spur-thighed tortoise (Testudo graeca) was studied with the aims of exploring: (i) the variation in diet among males, females and juveniles, (ii) the relationships between consumption and relative availability of the plant species, and (iii) which plant tissues, vegetative or reproductive, are eaten by tortoises. We recorded more than forty plant species at the study area, with monocot species (n = 7) having a greater percent cover than that of dicot species (n = 31 species) or Gymnospermae (n = 2). Tortoise diet was studied by categorising 4422 plant and animal fragments in faecal pellets of 20 males, 16 females and eight juveniles. Tortoises ate a wide variety of plant species, including 13 dicots and three monocots, and occasionally invertebrates. The number of fragments for a plant species was correlated with plant species cover, and plant vegetative tissues exceeded plant reproductive tissues in the faeces. Dicots (Fabaceae, Composeae, Primulaceae, and Caryophyllaceae) accounted for over 70% of the diet (faecal fragments). The high dietary (niche) overlap, and null model analysis (RA3 algorithm with 30,000 Monte Carlo simulations), indicate that males, females and juveniles did not partition food resources; all three groups ate the same plant species.
QScience Connect, 2015
We report, for the first time, evidence of predation by a shrike (Lanius sp.) on the lizard Mesalina adramitana. This is the first record of predation by shrikes on lizards in Qatar. Whilst we did not directly observe the event, the presence of shrikes in the area and the method of impalement indicate shrikes as the predator. The lizard was found freshly impaled on a palm tree (Phoenix dactylifera), at 150 cm above ground. Bird species of the genus Lanius are well-known predators of lizards, and in arid environments reptiles are likely common prey for these birds. We provide a review of literature concerning predatory events by shrikes on reptiles and amphibians. We suggest inspection of shrubs for animals impaled by shrikes can improve biodiversity inventories, complementing other commonly used methods.
Animal Biology, 2007
Demography and population biology aspects of the Moorish tortoise, Testudo graeca graeca were studied in the Parc National d'El Kala, north-eastern Algeria. Density, which was assessed by capture-mark-recapture procedures in a study plot of 30 ha surface, was 3.73 individuals× ha −1 . Adult sex-ratio was nearly equal (1.06 : 1). Sexual maturity was reached at 7-8 years of age in the males and at 9-11 years in the females. The mean age of tortoises was 13.8 ± 6.4 years (n = 88). Maximum longevity was over 20 years in both sexes. The females reached larger body size than the males. The growth was rapid during the early years of age in both sexes, and tended to stop completely by the 9-12 years of life in the males and by the 8-10 years in the females. The instantaneous growth of adults which were recaptured in multiple years indicated an average growth rate of 11.34 mm/year in the males, and of 26.30 mm/year in the females. Mortality was estimated at 3.94%. The main mortality cause for the tortoises of this population was the occurrence of fires spreading throughout the study area. These data are of interest because demographic patterns of Testudo graeca seem to vary not only because of their relative genetical variability, but also because of their relative environmental stress.
Acta Oecologica, 1998
A low breeding success (36.5 %) due primarily to nest predation by mammals, birds and reptiles has been found in the Woodchat Shrike Lanius srnator at three study sites in Mediterranean France. Data collected for 3 years on natural and artificial nests showed no year, time, season or spatial effect on nest predation rate in this species. No particular spatial breeding strategy is used, breeding success being no better at any nest site currently used along roadsides or far from roads. With respect to nest predation pressures, the best breeding strategy for Woodchat Shrike should be to breed as early as possible at any suitable site within its territory. Nevertheless, the impact of high predation on the viability of the studied populations of this species cannot be fully explained by the large impact of habitat transformations (closure of open, bushy grasslands) on current day populations. 0 Elsevier, Paris breeding success / nest predation / artificial nest / nest site / Zmzius senator