High density of herbivore populations can lead to intense foraging competition and depletion of food consequently lowering diet quality and population performance. We tested for the effects of the density of eastern black rhinoceros (Diceros bicornis michaeli) in nine in situ populations of 0.01-0.7 individuals per km(2) density range on the quality of their diet while controlling for plant available moisture and plant available nutrients. We used faecal calcium, phosphorus, copper and zinc concentrations as proxy indices for dietary quality from 473 fresh faecal samples obtained from 77 adult animals in situ, after determining a positive faeces-diet mineral correlation in feeding trials with black rhinoceros in zoos. Some populations surpassed 70%-80% of their estimated maximum stocking densities expected to cause impact on forage. However, we did not find significant correlation between rhino population density and dietary quality, as measured via faecal mineral nutrient content. This suggests that black rhinoceros may have sufficient behavioural plasticity to adjust their diet to cover their nutritional requirements when density increases. Instead, 1-month lagged plant available moisture, reflecting precipitation over the 4 weeks preceding each sampling effort, significantly explained the mineral concentrations in the faeces. By contrast, plant available nutrients had no effect.

Cape Wagtails Motacilla capensis have been identified as a species susceptible to infection by the mite Knemidokoptes jamaicensis, but the processes influencing infection rates and prevalence have not been studied. We assessed the mite infection level of 117 Cape Wagtails captured during the 2005 breeding season on Dassen Island, South Africa, analysed mite infection as functions of morphometrics and fat, and compared prevalence to other sites. Knemidokoptic mite infection was found in 42% of wagtails, which was more than double the prevalences reported for conspecifics on the mainland, and high compared to other host species. Mite infection of birds captured on the island was explored graphically against the morphometrics of individuals using cubic splines. Formal statistics were then applied using generalised linear mixed models, with observation and unique ring number as random effects within a two-level hierarchical mixed binomial model, and the fixed explanatory morphometric data being natural log-transformed. Morphometric data supported the idea that larger individuals were more likely to exhibit signs of mite infection. Possible contributing factors to this high percentage of mite-infected wagtails are discussed, with one possibility being that the low levels of predation on the island allow larger individuals to carry the cost of mite infection.

Many animals gain benefits from living in groups, such as a dilution in predation risk when they are closely aggregated (referred to as the 'selfish herd'). Game theory has been used to predict many properties of groups (such as the expected group size), but little is known about the proximate mechanisms by which animals achieve these predicted properties. We explore a possible proximate mechanism using a spatially explicit, individual-based model, where individuals can choose to rest or forage on the basis of a rule-of-thumb that is dependent upon both their energetic reserves and the presence and actions of neighbours. The resulting behaviour and energetic reserves of individuals, and the resulting group sizes, are shown to be affected both by the ability of the forager to detect conspecifics and areas of the environment suitable for foraging, and by the distribution of energy in the environment. The model also demonstrates that if animals are able to choose (based upon their energetic reserves) between selecting the best foraging sites available and moving towards their neighbours for safety, then this also has significant effects upon individuals and group sizes. The implications of the proposed rule-of-thumb are discussed.

A fundamental goal of conservation science is to improve conservation practice. Understanding species extinction patterns has been a central approach towards this objective. However, uncertainty remains about the extent to which species-level patterns reliably indicate population phenomena at the scale of local sites, where conservation ultimately takes place. Here, we explore the importance of both species- and site-specific components of variation in local population declines following habitat disturbance, and test a suite of hypotheses about their intrinsic and extrinsic drivers. To achieve these goals, we analyse an unusually detailed global dataset for species responses to habitat disturbance, namely primates in timber extraction systems, using cross-classified generalized linear mixed models. We show that while there are consistent differences in the severity of local population decline between species, an equal amount of variation also occurs between sites. The tests of our hypotheses further indicate that a combination of biological traits at the species level, and environmental factors at the site level, can help to explain these patterns. Specifically, primate populations show a more marked decline when the species is characterized by slow reproduction, high ecological requirements, low ecological flexibility and small body size; and when the local environment has had less time for recovery following disturbance. Our results demonstrate that individual species show a highly heterogeneous, yet explicable, pattern of decline. The increased recognition and elucidation of local-scale processes in species declines will improve our ability to conserve biodiversity in the future.

Background Foraging in groups offers animals a number of advantages, such as increasing their likelihood of finding food or detecting and avoiding predators. In order for a group to remain together, there has to be some degree of coordination of behaviour and movement between its members (which may in some cases be initiated by a decision-making leader, and in other cases may emerge as an underlying property of the group). For example, behavioural synchronisation is a phenomenon where animals within a group initiate and then continue to conduct identical behaviours, and has been characterised for a wide range of species. We examine how a pair of animals should behave using a state-dependent approach, and ask what conditions are likely to lead to behavioural synchronisation occurring, and whether one of the individuals is more likely to act as a leader. Results The model we describe considers how the energetic gain, metabolic requirements and predation risks faced by the individuals affect measures of their energetic state and behaviour (such as the degree of behavioural synchronisation seen within the pair, and the value to an individual of knowing the energetic state of its colleague). We explore how predictable changes in these measures are in response to changes in physiological requirements and predation risk. We also consider how these measures should change when the members of the pair are not identical in their metabolic requirements or their susceptibility to predation. We find that many of the changes seen in these measures are complex, especially when asymmetries exist between the members of the pair. Conclusion Analyses are presented that demonstrate that, although these general patterns are robust, care needs to be taken when considering the effects of individual differences, as the relationship between individual differences and the resulting qualitative changes in behaviour may be complex. We discuss how these results are related to experimental observations, and how the model and its predictions could be extended.

Longitudinal observations on known individuals are an important source of data with which to test evolutionary theory within natural populations, in particular, the evolution and maintenance of life-history traits. In this paper, we concentrate on the reproductive behaviour and survival of a small passerine bird, the great tit ( Parus major). The dataset we consider is taken from the long-term study of great tits in Wytham Woods in Oxfordshire. The models we consider are designed to relate variation in several phenotypic response variables that are linked to evolutionary fitness, alongside the correlations between them, to both general environmental and individual-specific factors. We fit multivariate cross-classified random effects models using a Markov chain Monte Carlo (MCMC) estimation algorithm described in the paper. Our results show for which traits variability is influenced by environmental factors and for which traits individual bird factors are more important. The partitioning of correlations is particularly illuminating, producing some pairs of ‘antagonistic’ correlations which are biologically meaningful.

What determines the vulnerability of protected areas, a fundamental component of biodiversity conservation, to political instability and warfare? We investigated the efficacy of park protection at Garamba National Park (Democratic Republic of Congo) before, during and after a period of armed conflict. Previous analysis has shown that bushmeat hunting in the park increased fivefold during the conflict, but then declined, in conjunction with changes in the sociopolitical structures (social institutions) that controlled the local bushmeat trade. We used park patrol records to investigate whether these changes were facilitated by a disruption to anti-poaching patrols. Contrary to expectation, anti-poaching patrols remained frequent during the conflict (as bushmeat offtake increased) and decreased afterwards (when bushmeat hunting also declined). These results indicate that bushmeat extraction was determined primarily by the social institutions. Although we found a demonstrable effect of anti-poaching patrols on hunting pressure, even a fourfold increase in patrol frequency would have been insufficient to cope with wartime poaching levels. Thus, anti-poaching patrols alone may not always be the most cost-effective means of managing protected areas, and protected-area efficacy might be enhanced by also working with those institutions that already play a role in regulating local natural-resource use.

In socially foraging animals, it is widely acknowledged that the position of an individual within the dominance hierarchy of the group has a large effect upon its foraging behaviour and energetic intake, where the intake of subordinates can be reduced through socially mediated interference. In this paper, we explore the effects of interference upon group dynamics and individual behaviour, using a spatially explicit individual-based model. Each individual follows a simple behavioural rule based upon its energetic reserves and the actions of its neighbours (where the rule is derived from game theory models). We show that dominant individuals should have larger energetic reserves than their subordinates, and the size of this difference increases when either food is scarce, the intensity of interference suffered by the subordinates increases, or the distance over which dominant individuals affect subordinates increases. Unlike previous models, the results presented in this paper about differences in reserves are not based upon prior assumptions of the effects of social hierarchy and energetic reserves upon predation risk, and emerge through nothing more than a reduction in energetic intake by the subordinates when dominants are present. Furthermore, we show that increasing interference intensity, food availability or the distance over which dominants have an effect also causes the difference in movement between ranks to increase (where subordinates move more than dominants), and the distance over which dominants have an effect changes the size of the groups that the different ranks are found in. These results are discussed in relation to previous studies of intra- and interspecific dominance hierarchies.

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m-2). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote.A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81% of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3%), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93% of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.

Cyclicity in behaviours, including reproduction, in relation to the lunar cycle is widely documented in some phyla, but weak or unknown in Class Mammalia. In this paper we present long-term video surveillance data of wild Eurasian badgers Meles meles, which reveal a strong correlation between reproductive behaviour and the lunar cycle. Squat marking and raised-leg urination, which increase in frequency at times of reproductive activity, showed maxima around day 22 of the lunar cycle (i.e. new moon). These findings were supported by observations of matings, together with published records, which showed significantly higher occurrence in the lunar dark phase (last quarter to first quarter). We propose that the lunar cycle has the potential to act as a regulator of the reproductive cycle in the badger.

Geese have to satisfy the high energy demands of flight with a low-energy and bulky food. When feeding on food items that are concentrated and widespread, as is the case in geese. an individual's instantaneous intake rate is largely determined by its bite size. Inter-individual variation in bite size was measured in barnacle geese Brania leucopsis, with the hypotheses that bite size would scale with (sward height)(a), where 0 < a < 1. and (bill lengith)(b), where b = 3.0, and that there would be a positive interaction between these explanatory variables. Using a generalized linear mixed modelling analysis, bite size was found not to vary over the measured sward heights, whilst bite size was found to scale with bill length to the power b = 14.24 (SE = 2.05). There was no significantly delectable interaction between these terms, indicating that barnacle geese with longer bills had larger bite sizes over the full range of sward heights studied. Bill length scaled with body mass to the Power 0.21 (SE = 0.01). Combining this with the scaling of bite size to bill length, we conclude that bite size scales with body mass to the power 2.99. Our results suggest that larger barnacle geese have a disproportionately larger bite size than smaller geese, which may explain the fitness advantages of larger geese observed in other studies. How-ever. smaller geese may resist this selection pressure by selectively consuming more nutritious plant parts or altering their bite rates.

It is commonly assumed that anti‐predator vigilance by foraging animals is costly because it interrupts food searching and handling time, leading to a reduction in feeding rate. When food handling does not require visual attention, however, a forager may handle food while simultaneously searching for the next food item or scanning for predators. We present a simple model of this process, showing that when the length of such compatible handling time Hc is long relative to search time S, specifically Hc/S > 1, it is possible to perform vigilance without a reduction in feeding rate. We test three predictions of this model regarding the relationships between feeding rate, vigilance and the Hc/S ratio, with data collected from a wild population of social foragers (samango monkeys, Cercopithecus mitis erythrarchus). These analyses consistently support our model, including our key prediction: as Hc/S increases, the negative relationship between feeding rate and the proportion of time spent scanning becomes progressively shallower. This pattern is more strongly driven by changes in median scan duration than scan frequency. Our study thus provides a simple rule that describes the extent to which vigilance can be expected to incur a feeding rate cost.

Summary Inequalities between individuals represent a major force driving patterns of animal dispersion. Here we use a novel approach to the analysis of feeding competition in large groups, based on photographic sequences of barnacle goose flocks over time. The spatial distributions of individuals derived from these photos were used to describe how individual feeding performance may be affected by patch depletion caused by other members of the flock. This was assessed indirectly by estimating the variation in prior grazing time experienced by individuals. The most successful foragers in a flock (i.e. those experiencing the least prior grazing time) are largely unaffected by depletion arising during the life span of the flock, while the least successful foragers experience very substantial depletion. Furthermore, for the less successful individuals, the average level of depletion increases continuously with both flock size and time spent in the flock. Skew in depletion experienced could not be assessed accurately, although it is likely that there is moderate right skew, i.e. a few individuals do very badly, but more than half do better than the mean. This study suggests that the degree of depletion experienced is related to position within the group, while previous studies of this system have shown that there is strong competition for the better positions. Dominance status is therefore likely to be a strong determinant of feeding performance. Subordinate individuals, being unable to obtain leading positions, may be forced to adopt alternative strategies to improve feeding performance, such as moving more frequently in order to maximize time in smaller or more recently formed groups.

Traits that are closely associated with fitness tend to have lower heritabilities (h2) than those that are not. This has been interpreted as evidence that natural selection tends to deplete genetic variation more rapidly for traits more closely associated with fitness (a corollary of Fisher's fundamental theorem), but Price and Schluter (1991) suggested the pattern might be due to higher residual variance in traits more closely related to fitness. The relationship between 10 different traits for females, seven traits for males, and overall fitness (lifetime recruitment) was quantified for great tits (Parus major) studied in their natural environment of Wytham Wood, England, using data collected over 39 years. Heritabilities and the coefficients of additive genetic and residual variance (CVA and CVR, respectively) were estimated using an "animal model." For both males and females, a trait's correlation (r) with fitness was negatively related to its h2 but positively related to its CVR. The CVA was not related to the trait's correlation with fitness in either sex. This is the third study using directly measured fitness in a wild population to show the important role of residual variation in determining the pattern of lower heritabilities for traits more closely related to fitness.

Since 1994 the Barnacle Goose Management Scheme (BGMS) has integrated conservation and agricultural aims on the Scottish side of the Solway Firth. In the 4 years before the introduction of the BGMS, the density of barnacle geese (Branta leucopsis) on the Wildfowl & Wetlands Trust Reserve at Caerlaverock was four times higher than on the non-Reserve area. In the 6 years following establishment of the BGMS, the density of geese on non-Reserve fields rose so that the Reserve had twice the density of the non-Reserve area. No difference in density was found between fields in the Feeding Zone and Intermediate Zone of the BGMS. The density of barnacle geese around the study area appears to be at a maximum under current management regimes. The remaining geese from this increasing population are using other feeding areas. This may lead to further conservation-agriculture conflict in the future, but could be mitigated through expanding the range and quality of the BGMS, through increasing the dedicated reserve network, or through a combination of the two.

Studies of variation in individual reproductive fitness in natural populations have been important in the development of life-history biology, in particular for our understanding of the evolution of reproductive scheduling, reproductive effort and the individual optimisation of fitness. Most long-term studies of marked individuals are characterised by complex data sets, where repeated observations of individuals, distributed over a range of environments, make the determination of the important sources of variation between individuals difficult. In addition, many traits measured in individuals show strong phenotypic covariance, which can arise for numerous reasons; distinguishing between these explanations is difficult without experimentation. In this paper we apply Bayesian cross-classified multivariate models to data from a long-term study of the great tit Parus major to partition the covariance between different reproductive parameters (life history traits) within and between differing sources of variance. Our analyses provide evidence for the importance of the environment in structuring patterns of phenotypic covariance between pairs of lifehistory traits. Additionally, these analyses reveal patterns of antagonistic covariance at different levels of the analysis, which seem to reflect the opposing influence of (i) individual variation (particularly among females) in acquisition of resources and (ii) trade-offs between life-history traits. We argue that the multi-level partitioning of covariance offers some alternative perspectives as a means of causal analysis of lifehistory variation, and suggest some additional approaches that could be taken using this method.

The grazing of agricultural pastures during winter and spring by geese is considered an important agricultural problem in parts of the U.K. This study describes the sward structure, leaf extension and senescence rates of Lolium perenne -dominated pastures that are frequently grazed by barnacle geese (Branta leucopsis) during winter in South-west Scotland, as well as the conducting of a field experiment that simulated grazing to investigate the effects of defoliation. Gross leaf extension and senescence rates were strongly related to temperature, daylength and average tiller size, resulting in positive values of net leaf extension rate per tiller for most of the winter. Total tiller length declined from November to January but increased from January to April. Sward height, however, declined consistently from October to April, suggesting that swards were becoming trampled by repeated visits by flocks of geese over this time. The structure of individual tillers was found to vary slightly over the winter, with tillers becoming more dominated by younger leaves towards the end of the winter. Experimental defoliation of tillers suggested that absolute leaf extension rates did not respond in an under- or over-compensatory manner, even when tillers were nearly completely defoliated. The results suggested that sward structure and leaf extension rates are not unduly affected by repeated grazing by overwintering geese and that short-term depletion and trampling are the main impacts.

Animals that forage socially1 often stand to gain from coordination of their behaviour2,3,4,5. Yet it is not known how group members reach a consensus on the timing of foraging bouts. Here we demonstrate a simple process by which this may occur. We develop a state-dependent, dynamic game model6 of foraging by a pair of animals, in which each individual chooses between resting or foraging during a series of consecutive periods, so as to maximize its own individual chances of survival6,7. We find that, if there is an advantage to foraging together1,2,8, the equilibrium behaviour of both individuals becomes highly synchronized. As a result of this synchronization, differences in the energetic reserves of the two players spontaneously develop, leading them to adopt different behavioural roles. The individual with lower reserves emerges as the ‘pace-maker’ who determines when the pair should forage, providing a straightforward resolution to the problem of group coordination. Moreover, the strategy that gives rise to this behaviour can be implemented by a simple ‘rule of thumb’9 that requires no detailed knowledge of the state of other individuals.

The amount of nuclear DNA extracted from teeth of 279 individual red fox Vulpes vulpes collected over a period spanning the last three decades was determined by quantitative polymerase chain reaction (PCR). Although teeth were autoclaved during initial collection, 73.8% of extracts contained sufficient DNA concentration (> 5 pg/muL) suitable for reliable microsatellite genotyping but the quantity of nuclear DNA decayed significantly over time in a nonlinear pattern. The success of PCR amplification across four examined canine microsatellites over time was dependent on fragment size. By including data from two different tests for human contamination and from frequencies of allelic dropout and false alleles, the methodological constraints of population genetic studies using microsatellite loci amplified from historic DNA are discussed.