Birth sex ratios in sheep over nine lambing seasons: years 7–9 and the effects of ageing

The birth sex ratio of a commercial flock of Suffolk cross sheep, Ovis aries, was studied over nine consecutive lambing seasons. In all data from 2704 lambs were recorded and analysed. The overall (1985–1993) birth sex ratio was 49.96% male lambs. Ewes with single lambs produced significantly more males (53.04%) than ewes with triplets (45.54% male). A significant positive correlation was found between the flock age and the birth sex ratio (1985–1992). As the flock aged the birth sex ratio changed from female biased to male biased, remained male biased for a number of years, and then became female biased again. This pattern is evident first in single, then in twin and later in triplet births. Among like sex twins (males and females) (1985–1993) more males (53.88%) were born in the first half and more females (45.57% males) in the second half of the lambing season. The difference between the two halves is significant.     

Land-use changes and implications for management of a small protected island off the coast of Bretagne

Over the 20th century, reduced land cultivation has caused an extension of fallow land in several European countries, which has led to a decrease in biodiversity. Knowledge of dynamic vegetation processes and of the impact of human activities on biodiversity provides the basis for land management recommendations, as well as for wildlife management programs. We analysed land-use changes on a small protected island (Ushant, Bretagne, France) using historical documentation (1844) and aerial photographs taken in 1952 and 1992. Over this period, especially during the last 40 yr, Ushant underwent a complete transformation from rural landscape to extensive shrubland. No cultivated area remains, grazed areas were moved from the coastal fringe to the core of the island, while over 40% of the island is fallow land. The relationship between current sheep grazing and vegetation suggests that grazed meadows used to be close to inhabited areas, i.e. 150 m outside the villages. These results allowed us to analyse landcover potential related to changes in the intensity of sheep grazing. The scenarios highlighted by our method provide an objective framework for further assessment of fallow land management.     

Effects of Protective Fencing on Birds, Lizards, and Black-Tailed Hares in the Western Mojave Desert

Lepus californicus ), perennial plant cover, and structural diversity of perennial plants were evaluated from spring 1994 through winter 1995 at the Desert Tortoise Research Natural Area (DTNA), in the Mojave Desert, California. Abundance and species richness of birds were higher inside than outside the DTNA, and effects were larger during breeding than wintering seasons and during a high than a low rainfall year. Ash-throated flycatchers (Myiarchus cinerascens), cactus wrens (Campylorhynchus brunneicapillus), LeConte's thrashers (Toxostoma lecontei), loggerhead shrikes (Lanius ludovicianus), sage sparrows (Amphispiza belli), and verdins (Auriparus flaviceps) were more abundant inside than outside the DTNA. Nesting activity was also more frequent inside. Total abundance and species richness of lizards and individual abundances of western whiptail lizards (Cnemidophorous tigris) and desert spiny lizards (Sceloporus magister) were higher inside than outside. In contrast, abundance of black-tailed hares was lower inside. Structural diversity of the perennial plant community did not differ due to protection, but cover was 50% higher in protected areas. Black-tailed hares generally prefer areas of low perennial plant cover, which may explain why they were more abundant outside than inside the DTNA. Habitat structure may not affect bird and lizard communities as much as availability of food at this desert site, and the greater abundance and species richness of vertebrates inside than outside the DTNA may correlate with abundances of seeds and invertebrate prey.     

Nomadic pastoralists adopt subsistence strategies that maximise long-term household survival

Summary Optimality approaches have been used to investigate the adaptiveness of human subsistence strategies mainly in hunter-gatherer societies. However the static optimality models used are not suitable for investigating the long-term costs and benefits of decisions, especially in societies where wealth is accumulated and hence resources gained in one year have an influence on future years. Here I use dynamic optimality modelling to investigate the adaptiveness of a subsistence strategy in the Gabbra, a nomadic pastoralist group. I show that herders forego short-term gain in favour of long-term household survival. This is done by herders sometimes manipulating the life histories of their sheep. In herds where the breeding rate has been slowed, by restricting ewes access to males, females have greater longevity, but fewer offspring per year, than in unmanipulated herds. Models maximising offtake from the herd predict that herd breeding-rate should never be slowed. Models maximising short-term household survival predict herd-breeding rate should always be slowed. Models of long-term household survival predict that herd-breeding rate should be slowed only by relatively wealthy households. This is the behaviour observed. Poor and wealthy house-holds adopt different behaviours, yet all are following optimal strategies for their own level of wealth, that maximise their long-term survival. This is the behaviour that would be predicted on the basis of evolutionary theory, given that a family takes many years to be raised. Correspondence to: R. Mace