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Herd Size (herd + size)
Selected AbstractsSocio-Spatial Relationships in Dairy CowsETHOLOGY, Issue 1 2010Lorenz Gygax Farm animals may serve as models for evaluating social networks in a controlled environment. We used an automated system to track, at fine temporal and spatial resolution (once per minute, ±50 cm) every individual in six herds of dairy cows (Bos taurus). We then analysed the data using social network analyses. Relationships were based on non-random attachment and avoidance relationships in respect to synchronous use and distances observed in three different functional areas (activity, feeding and lying). We found that neither synchrony nor distance between cows was strongly predictable among the three functional areas. The emerging social networks were tightly knit for attachment relationships and less dense for avoidance relationships. These networks loosened up from the feeding and lying area to the activity area, and were less dense for relationships based on synchronicity than on median distance with respect to node degree, relative size of the largest cluster, density and diameter of the network. In addition, synchronicity was higher in dyads of dairy cows that had grown up together and shared their last dry period. This last effect disappeared with increasing herd size. Dairy herds can be characterized by one strongly clustered network including most of the herd members with many non-random attachment and avoidance relationships. Closely synchronous dyads were composed of cows with more intense previous contact. The automatic tracking of a large number of individuals proved promising in acquiring the data necessary for tackling social network analyses. [source] An assessment of the puku (Kobus vardonii Livingstone 1857) population at Lake Rukwa, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Matthias Waltert Abstract The population of puku, Kobus vardonii, at Lake Rukwa, one of only two in Tanzania, is poorly known. A multi-species dry season game count carried out in Rukwa Game Reserve (RGR) in 2004 estimated a population size of 1729, but was associated with a high margin of error [coefficient of variation (CV) 0.88]. To increase the precision for the local puku population estimate, we conducted a zig-zag line transect survey restricted only to areas occupied by puku in the dry season of 2006. This survey technique produced an estimate of 776 individuals and the CV was considerably reduced to 0.29. Puku herd size was comparable with the studies carried out in the Kilombero valley, Tanzania and in Kasanka National Park, Zambia, thus broadly confirming the herding ecology of this species. We found that pukus were restricted to the central parts of the floodplains, suggesting an avoidance of habitats used by pastoralists at the edge of RGR. Compared with the estimates of the puku population made in the 1980s, the puku population has declined. We recommend regular monitoring and enforcement of the current management plan to conserve the local puku population. Résumé Le statut de la population du puku Kobus vardonii au lac Rukwa, une des deux seules populations de Tanzanie, est mal connu. Un dénombrement de nombreuses espèces animales réalisé en saison sèche dans la Réserve de Faune de Rukwa (RGR) en 2004 a estimé la taille de la population à 1 729, mais ce chiffre était associéà une grande marge d'erreur (CV 0,88). Pour améliorer la précision de l'estimation de la population de pukus, nous avons mené une étude par transect en zigzag limitée aux zones occupées par les pukus, pendant la saison sèche de 2006. Cette technique d'étude a donné une estimation de 776 individus, et la CV était considérablement réduite, à 0,29. La taille des hardes de pukus était comparable à celle relevée dans la vallée de Kilombero, en Tanzanie, et dans le Parc National de Kasanka, en Zambie, confirmant ainsi l'écologie en harde de cette espèce. Nous avons découvert que les pukus se limitaient aux parties centrales des plaines inondables, ce qui suggère qu'ils évitent les habitats fréquentés par les pasteurs à la limite de la Réserve de Faune de Rukwa. Comparée aux estimations de cette population de pukus réalisées dans les années 1980, cette population a décliné. Nous avons recommandé d'assurer un suivi régulier et d'appliquer le plan de gestion actuel pour conserver la population locale de pukus. [source] Foraging efficiency and vigilance behaviour of impala: the influence of herd size and neighbour densityAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009Sonja M. Smith Abstract Group foraging can be beneficial for ungulates by decreasing the time required for vigilance, but it can also prove costly because of competition. To determine responses to gregarious behaviour, we studied foraging activity and vigilance of impala (Aepyceros melampus) near Kruger National Park, South Africa. We measured time spent foraging, vigilant, moving, grooming, engaging in social interactions and determined herd size and group distribution (i.e. density). We calculated accepted food abundance (AFA), food ingestion rate, steps per minute and percent vigilance for female, bachelor male and herd male impala. There was no relationship between herd size and vigilance, but vigilance decreased with increasing density (t1,311 = 4.91, P <0.0001). Additionally, AFA decreased (t1,61 = 5.96, P <0.0001) and steps per minute increased (t1,311 = 14.38, P < 0.0001) as more individuals fed in close proximity to each other. Impala could be altering their behaviour to accommodate a perceived change in resources because of intraspecific competition and these adjustments might be related more to the distribution of herd members than to herd size. Further studies should examine the behaviour of gregarious animals in relation to the distribution of herd members in addition to group size. Résumé Le fait de se nourrir en groupe peut être avantageux pour les ongulés parce qu'il réduit le temps nécessaire à la surveillance, mais il peut aussi se révéler coûteux en termes de compétition. Pour déterminer les réponses à un comportement grégaire, nous avons étudié l'action de se nourrir et la vigilance chez l'impala (Aepyceros melampus) près du Parc National Kruger, en Afrique du Sud. Nous avons mesuré le temps passéà se nourrir, à surveiller, à se déplacer, au toilettage, à l'engagement dans des interactions sociales, et nous avons déterminé la taille de la harde et la distribution du groupe (c.-à-d. sa densité). Nous avons calculé l'abondance de nourriture acceptée (AFA), le taux d'ingestion de nourriture (FIR), les pas par minute et le pourcentage de vigilance chez les femelles, les mâles célibataires et les impalas mâles en hardes. Il n'y avait pas de relation entre la taille de la harde et la vigilance, mais la vigilance diminuait lorsque la densité augmentait (t1,311 = 4,91, P < 0,0001). De plus, l'AFA diminuait (t1,61 = 5,96, P < 0,0001), et le nombre de pas par minute augmentait (t1,311 = 14,38, P < 0,0001) lorsque des individus plus nombreux se nourrissaient très près les uns des autres. Les impalas pouvaient modifier leur comportement pour s'adapter à la perception d'un changement des ressources dûà la compétition intraspécifique, et ces ajustements pourraient bien être liés plus à la distribution des membres de la harde qu'à sa taille. De nouvelles études devraient examiner le comportement des animaux grégaires en fonction de la distribution des membres de la harde, en plus de la taille du groupe. [source] The role of water abundance, thermoregulation, perceived predation risk and interference competition in water access by African herbivoresAFRICAN JOURNAL OF ECOLOGY, Issue 3 2008Marion Valeix Abstract In African savannas, surface water can become limiting and an understanding of how animals address the trade-offs between different constraints to access this resource is needed. Here, we describe water access by ten African herbivore species in Hwange National Park, Zimbabwe, and we explore four possible determinants of the observed behaviours: water abundance, thermoregulation, perceived predation risk and interference competition. On average, herbivores were observed to drink in 80% of visits to a waterhole. The probability of drinking was higher in 2003 (474 mm) than in 2004 (770 mm), and at the end of the dry season than at its beginning. For larger species, this probability may also be related to risks of interference competition with elephants or other herbivores. For smaller species, this probability may also be related to the perceived risk of predation. We also investigate the time spent accessing water to drink. The influence of herd size and the presence of young on the time spent accessing water for most species suggests that perceived predation risk plays a role. Thermoregulation also affects this time: during the hottest periods, herbivores spend less time in open areas, unless when wind is strong, probably owing to evapotranspired heat loss. Résumé Dans les savanes africaines, l'eau de surface disponible peut devenir un facteur limitant et il est nécessaire de comprendre comment les animaux agissent face aux différentes contraintes que pose l'accès à cette ressource. Nous décrivons ici l'accès à l'eau de dix herbivores africains du Parc National de Hwange, au Zimbabwe, et nous explorons quatre facteurs qui sont peut-être déterminants dans les comportements observés: l'abondance de l'eau, la thermorégulation, le risque de prédation ressenti et la compétition/ interférence. En moyenne, on a observé que les herbivores buvaient lors de 80% de leurs visites au point d'eau. La probabilité qu'ils boivent étai plus forte en 2003 (474 mm) qu'en 2004 (770 mm), et à la fin de la saison sèche qu'au début. Pour les plus grandes espèces, cette probabilité pourrait aussi être liée aux risques de compétition par interférence avec les éléphants ou d'autres herbivores. Pour les plus petites espèces, cette probabilité pourrait aussi être liée au risque de prédation ressenti. Nous avons aussi étudié le temps passéà se rendre au point d'eau pour y boire. L'influence de la taille du groupe et de la présence de jeunes sur le temps pris par la plupart des espèces pour se rendre au point d'eau laisse penser que la perception du risque de prédation joue un rôle. La thermorégulation affecte aussi cette durée: pendant les périodes les plus chaudes, les herbivores passent moins de temps dans les espaces ouverts, sauf si le vent est fort, probablement à cause de la perte de chaleur par évapotranspiration. [source] Is there safety in numbers?MEDICAL AND VETERINARY ENTOMOLOGY, Issue 4 2007The effect of cattle herding on biting risk from tsetse flies Abstract In sub-Saharan Africa, tsetse (Glossina spp.) transmit species of Trypanosoma which threaten 45,50 million cattle with trypanosomiasis. These livestock are subject to various herding practices which may affect biting rates on individual cattle and hence the probability of infection. In Zimbabwe, studies were made of the effect of herd size and composition on individual biting rates by capturing tsetse as they approached and departed from groups of one to 12 cattle. Flies were captured using a ring of electrocuting nets and bloodmeals were analysed using DNA markers to identify which individual cattle were bitten. Increasing the size of a herd from one to 12 adults increased the mean number of tsetse visiting the herd four-fold and the mean feeding probability from 54% to 71%; the increased probability with larger herds was probably a result of fewer flies per host, which, in turn, reduced the hosts' defensive behaviour. For adults and juveniles in groups of four to eight cattle, > 89% of bloodmeals were from the adults, even when these comprised just 13% of the herd. For groups comprising two oxen, four cows/heifers and two calves, a grouping that reflects the typical composition of communal herds in Zimbabwe, , 80% of bloodmeals were from the oxen. Simple models of entomological inoculation rates suggest that cattle herding practices may reduce individual trypanosomiasis risk by up to 90%. These results have several epidemiological and practical implications. First, the gregarious nature of hosts needs to be considered in estimating entomological inoculation rates. Secondly, heterogeneities in biting rates on different cattle may help to explain why disease prevalence is frequently lower in younger/smaller cattle. Thirdly, the cost and effectiveness of tsetse control using insecticide-treated cattle may be improved by treating older/larger hosts within a herd. In general, the patterns observed with tsetse appear to apply to other genera of cattle-feeding Diptera (Stomoxys, Anopheles, Tabanidae) and thus may be important for the development of strategies for controlling other diseases affecting livestock. [source] Stochastic wealth dynamics and risk management among a poor population,THE ECONOMIC JOURNAL, Issue 498 2004Travis J. Lybbert We use herd history data collected among pastoralists in southern Ethiopia to study stochastic wealth dynamics among a poor population. Although covariate rainfall shocks plainly matter, household-specific factors, including own herd size, account for most observed variability in wealth dynamics. We find no support for the tragedy of the commons hypothesis. Past studies may have conflated costly self-insurance with stocking rate externalities. Biophysical shocks move households between multiple dynamic wealth equilibria , the lowest suggesting a poverty trap , according to nonconvex path dynamics. These findings have broad implications for development and relief strategies among a poor population vulnerable to climatic shocks. [source] Effect of frequency of application of inorganic nitrogen fertilizer within a rotational paddock-grazing system on the performance of dairy cows and inputs of labourGRASS & FORAGE SCIENCE, Issue 2 2008C. P. Ferris Abstract As herd sizes and labour costs increase, and the availability of skilled labour decreases, efficient use of available labour becomes more important in dairy cow systems. Two experiments were conducted to examine the effect of reducing the frequency of application of inorganic nitrogen (N) fertilizer on inputs of labour and performance of dairy cows. Experiments 1 (duration of 169 d) and 2 (duration of 179 d) involved fifty-eight and forty multiparous Holstein,Friesian dairy cows, respectively, in mid-lactation. In each experiment, in the ,infrequent' treatment fertilizer was applied to all paddocks on a single occasion at the start of each grazing cycle, while in treatment ,frequent', fertilizer was applied on three occasions each week, within 2 or 3 d of each paddock having been grazed. The experimental treatments were started from 30 March and 29 March in Experiments 1 and 2 respectively. Total N application rates were approximately 360 and 250 kg N ha,1 in Experiments 1 and 2 respectively. Concentrate feed (4·0 kg per cow) was offered daily in both experiments. With the ,infrequent' treatment, highest concentrations of crude protein and nitrate in herbage were observed in swards grazed approximately 10 d after N fertilizer was applied. Treatment had no significant effect on milk yield, milk fat and protein concentrations, and final live weight and body condition score of cows in either experiment. Milk urea and plasma urea concentrations were not significantly affected by treatment. Calculated application times of fertilizer for a herd of 100 dairy cows were 107 and 83 min week,1 for the ,frequent' and ,infrequent' treatments respectively. [source] Hunting differentially affects mixed-sex and bachelor-herds in a gregarious ungulate, the impala (Aepyceros melampus: Bovidae)AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Christiane Averbeck Abstract We investigated herd-sizes and herd-compositions of Impala (Aepyceros melampus) inside a protected area [Lake Mburo National Park (LMNP) in western Uganda] and the unprotected adjacent ranchland [the Ankole Ranching Scheme (ARS)]. Impala experience intense hunting and poaching in the study area, and poaching is especially strong on the ARS. We found evidence for changes in overall group-sizes in both mixed-sex and pure bachelor herds between areas in and outside LMNP. Mixed-sex herds strongly decreased in size outside the National Park, but bachelor herds even slightly increased in size. While the group-composition of mixed-sex herds was very similar in areas in and outside LMNP, bachelor herds comprised more yearlings and subadult males on the ARS. Our study suggests that effects of hunting and other human nuisance may differ between herd types: mixed herds probably decrease in size because females are more strongly hunted. Around LMNP, impala are usually hunted using nets and spears, thereby increasing the hunters' chance of being injured. Poachers therefore prefer hornless females (and their calves), as it is less dangerous to handle net-caught females than males. As a result, males are less hunted, but increased vigilance and, therefore, reduced aggression among the members of a bachelor herd, may account for the observed increase in herd sizes and changes in group-compositions. Résumé Nous avons étudié la taille et la composition des hardes d'impalas (Aepyceros melampus) dans une aire protégée, le Parc National du Lac Mburo (LMNP) dans l'ouest de l'Ouganda, et dans le ranch adjacent non protégé, le Ankole Ranching Scheme (ARS). Les impalas subissent une chasse et un braconnage intenses dans la région étudiée et le braconnage est particulièrement grave dans l'ARS. Nous avons découvert des preuves de changement de la taille moyenne des groupes, aussi bien dans les hardes mixtes que dans celles composées uniquement de mâles, entre les aires situées dans et en dehors du LMNP. La taille des hardes mixtes diminuait fortement hors du parc national alors que les hardes composées de mâles augmentaient légèrement. Alors que la composition des groupes mixtes était très semblable dans et en dehors de l'aire protégée, les groupes de mâles comprenaient plus de jeunes de l'année et de subadultes dans l'ARS. Notre étude laisse penser que les effets de la chasse et des autres nuisances d'origine humaine pourraient différer selon le type de harde: la taille des hardes mixtes se réduit probablement parce que les femelles sont chassées davantage. Autour du LMNP, les impalas sont d'habitude chassés au moyen de filets et de flèches, ce qui augmente les risques que les chasseurs soient blessés. Les braconniers préfèrent donc les femelles, sans cornes, et leurs jeunes parce qu'il est plus facile de manipuler des femelles prises dans des filets que des mâles. Par conséquent, les mâles sont moins chassés, et une plus grande vigilance et donc une moins forte agression entre les membres d'une harde de mâles peuvent expliquer en partie pourquoi la taille des hardes augmente et la composition des groupes varie. [source] The effects of flock size, habitat type and cattle herd sizes on feeding and vigilance in cattle egrets (Ardeola ibis)AFRICAN JOURNAL OF ECOLOGY, Issue 3 2003G. M. Wahungu No abstract is available for this article. [source] | ||||||||||