Abstract: In most cooperatively breeding birds and mammals, reproductive rates are lower for social subordinates than for dominants, and it is common for reproduction in subordinates to be completely suppressed. Early research conducted in captivity showed that losing fights can increase glucocorticoid (GC) secretion, a general response to stress. Because GCs can suppress reproduction, it has been widely argued that chronic stress might underlie reproductive suppression of social subordinates in cooperative breeders. Contradicting this hypothesis, recent studies of cooperative breeders in the wild show that dominant individuals have elevated GCs more often than do subordinates. The findings that elevated GCs can be a consequence of subordination or a cost of dominance complicate the conventional view of social stress, with broad ramifications for the evolution of dominance and reproductive suppression.

Abstract: In spite of the importance of grazed forage in horse nutrition, little information is available on their daily intake at pasture. We determined the intake of 4 non-breeding mares of a heavy breed (average body weight = 674 kg), grazing during the summer in heterogeneous natural grasslands of the Marais Poitevin (France), an internationally important wetland where grazing is an essential process which maintains biodiversity. The mares ate large quantities of forage (21.9 $pm$ 2.4 kg of organic matter per day, i.e. 166.2 $pm$ 20.8 g of organic matter per kg LW0.75 per day) in comparison with previous published values and with the estimated requirements of these horses. The use of the vegetation was very selective, the mares spent about 70% of their feeding time on short grass lawns (sward surface $leq$ 4 cm, biomass < 100 g$cdot$m-2), that represented only 10% of the area. This behaviour maintained the plants at young growing stages which are of better quality than ungrazed plants. These results are discussed in relation to the dynamics of the plant communities.

Abstract: Summary The aim of this study was to investigate the effect of gonadotrophin-releasing hormone (GnRH) immunisation on mature stallions that had been used for breeding. Four Standardbred stallions were used in the study: 3 experimental animals and 1 control animal. Semen was collected regularly, i.e. twice/week, during the 4 months prior to the experimental period. The stallions were immunised against GnRH with a GnRH-BSA conjugate. Equimune was used as the adjuvant. The stallions were immunised on 5 occasions, 4 at 2 week intervals, and the fifth 4 weeks after the fourth. Blood samples were taken once a week for analysis of GnRH antibody titre and every third week for testosterone and oestrone sulphate analyses. Semen was collected once a week, and libido and sexual behaviour were observed. Ejaculate volume, sperm concentration, total number of sperm in the ejaculate, sperm motility and sperm morphology were evaluated. Testicular size was measured once a week. At the end of the study, the stallions were castrated, and a histological examination of the testes performed. All immunised stallions produced antibodies against GnRH, and plasma testosterone concentration decreased. However, the effect of immunisation varied between stallions. In 2 of the stallions, high levels of antibodies were found, while in the third, the level was moderate. Four weeks after the first immunisation, a decrease in libido was observed. Two months after the first immunisation, marked changes in semen quality were observed in the 2 stallions with high antibody titres. Fourteen weeks after the first immunisation, the total number of sperm/ejaculate had decreased from >8.6×109 to<2.7×109, sperm motility from >59 to<10% and the frequency of morphological normal spermatozoa had decreased from >60 to<14%. The dominating abnormalities were abnormal head shapes, proximal cytoplasmic droplets and detached heads. In the third stallion, only slight changes in semen quality were found. No changes were observed in the control stallion. Decreases in testicular size were noted in all of the experimental stallions. Pronounced histological alterations in the testes were observed in 2 of the stallions. It is concluded that the vaccine was effective in stimulating production of GnRH antibodies and in suppressing testicular function and androgen secretion. However, there was an individual variation in the responses among the stallions and, further, libido was not totally suppressed.

Abstract: Description
The aim of Advances in the Study of Behavior remains as it has been since the series began: to serve the increasing number of scientists who are engaged in the study of animal behavior by presenting their theoretical ideas and research to their colleagues and to those in neighboring fields. We hope that the series will continue its “contribution to the development of the field”, as its intended role was phrased in the Preface to the first volume in 1965. Since that time, traditional areas of animal behavior have achieved new vigor by the links they have formed with related fields and by the closer relationship that now exists between those studying animal and human subjects. Advances in the Study of Behavior, Volume 31 continues to serve scientists across a wide spectrum of disciplines. Focusing on new theories and research developments with respect to behavioral ecology, evolutionary biology, and comparative psychology, these volumes foster cooperation and communications in these dense fields.
Audience
Experimental psychologists studying animal behavior, comparative psychologists, ethologists, evolutionary biologists, and ichthyologists.
Contents
Contributors. Preface.M.L. East and H. Hofer, Conflict and Co-operation in a Female Dominated Society: A Re-assessment of the “Hyper-aggressive” Image of Spotted Hyenas.C. ten Cate, H. Slabbekoorn, and M.R. Ballintijn, Bird Song and Male-male Competition: Causes and Consequences of Vocal Variability in the Collared Dove (Streptopelia Decaocto).R.W. Byrne, Imitation of Novel Complex Actions: What Does the Evidence from Animals Mean?L.J. Rogers, Lateralization in Vertebrates: Its Early Evolution, General Pattern and Development.S.H. Hulse, Auditory Scene Analysis in Animal Communication.P.K. Stoddard, Electric Signals: Predation, Sex, and Environmental Constraints.T. Aubin and P. Jouventin, How to Vocally Identify Kin in a Crowd: The Penguin Model. Index. Contents of Previous Volumes.

Abstract: Volumetric studies in a range of animals (London taxi-drivers, polygynous male voles, nest-parasitic female cowbirds, and a number of food-storing birds) have shown that the size of the hippocampus, a brain region essential to learning and memory, is correlated with tasks involving an extra demand for spatial learning and memory. In this paper, we report the quantitative advantage that food storers gain from such an enlargement. Coal tits () a food-storing species, performed better than great tits (), a nonstoring species, on a task that assessed memory persistence but not on a task that assessed memory resolution or on one that tested memory capacity. These results show that the advantage to the food-storing species associated with an enlarged hippocampus is one of memory persistence.