The elephant population in Kruger National Park, Republic of South Africa, is growing rapidly. To prevent damage to the Park's ecosystems, the management has culled about 7% of the population annually. Such culls are very controversial. At first glance, contraceptives seem an attractive alternative means of control. We examine contraception as a management option, review the relevant aspects of elephant reproduction, physiology and demography and conclude that this optimism is probably misplaced. First, contraceptives have a wide range of physiological and behavioural side-effects that may prove to be damaging to the individual female and those around her. Second, the elephants in the Park have near-maximal growth rates with inter-calving intervals of less than four years. To achieve zero population growth, about three-quarters of the adult female elephants would need to be on contraceptives. There are no simple alternatives. The smallest numerical target for controlling population numbers is to kill or sterilize females about to become pregnant for the first time. Such a solution is unlikely to appease those who consider killing elephants to be unethical. It may, however, be the one closest to the natural patterns of elephant mortality.

I used VORTEX to make a prior evaluation of the planned reintroduction project of the endangered bearded vulture (Gypaetus barbatus) in the mountains of southern Spain. The minimum size of a captive population needed to ensure the release of two bearded vulture fledglings per year is 30 individuals. If breeding success was improved, this minimum captive population could be reduced to 10 individuals. As the cost of the project is proportional to the size of the captive population, some research effort should be devoted to improving breeding success in captivity. The current size of the captive population — four individuals — is not enough to start the releases, even if the vultures were already breeding. The first step for the project should be to increase the size of the captive population. If on average one individual per year was added to the captive population, it would take 15 years to reach 30 individuals. If breeding in captivity was improved, it would take only three to seven years to reach the minimum captive population of 10 individuals. Once releases were started, the project would need on average 20 years to reach a goal of 15 adult pairs in the Cazorla mountains. Both the success of the project and the time necessary to reach this stated goal are very sensitive to the mortality rates in the wild. There is little known about these rates, and better estimates are urgently needed to improve the predictions of the models.

In a study correlating carnivore density with study area size, Smallwood & Schonewald (1996) suggested that for larger areas, biologists extrapolate from small, high-density study sites to many unstudied low density sites, but that this approach is invalid because of heterogeneous distribution of animals across the landscape. For wolves (Canis lupus), however, size of study areas may also be a consequence of density. Linear regression of data from 18 recent field studies of wolves indicates that study area size is correlated less strongly to mean numbers of wolves counted in an area (r2=0·24) than to wolf density (r2=0·85). When parameters representing biological features of each study area (average wolf pack territory size, ungulate biomass density index and predominant ungulate species), as well as logistical constraints of the study (number of packs), were made available for inclusion through a stepwise procedure, mean numbers of wolves counted were related (r2=0·94) to number of packs, ungulate biomass and deer, while density was related to both study area size and number of wolves counted (r2=0·91). Study area size was found to be strongly predicted (r2=0·96) by ungulate biomass, wolf territory size and wolf numbers. These results clearly reinforce the idea that biological parameters play an essential role in determining animal numbers and density. It also follows, as emphasized by Smallwood & Schonewald (1996, in press), that extrapolation of census or survey information to larger areas needs to be done carefully to account for actual variation in animal density.

Why Animal Conservation?

Conservation biology is a discipline that has come of age. Over the past ten–fifteen years we have seen it develop, from a topic that many academics saw as peripheral and quirky into mainstream biological science. Conservation biology is now routinely taught on degree level courses, the number of papers published in the specialist academic literature has risen exponentially, and the citation rates of those journals continue to increase.

Genetic variation was measured in 105 African buffalo from four populations in South Africa to investigate the effects of habitat fragmentation. Levels of heterozygosity, allelic diversity and genetic differentiation among populations were quantified using seven polymorphic microsatellite markers. There was a significant correlation between the amount of genetic variation and population size, and differentiation was detected among all populations measured by FST and RST. We used likelihood analysis to infer the effective population sizes of each population and to determine whether the fragmented populations were historically differentiated from one another. The genetic estimates of census size were consistent with historical records, and no historical genetic differentiation could be inferred in the original population before fragmentation. These results are discussed in the light of conservation management of fragmented buffalo populations, particularly where natural gene flow is no longer possible.

African wild dogs (Lycaon pictus) always live at low population densities relative to sympatric large carnivores. This suggests that there are basic ecological reasons for the wild dog's endangered status. We examined the effects of intraspecific and interspecific competition, infectious diseases, foraging success, genetics and human activities on wild dogs. We present data from wild dogs in the Selous Game Reserve, and make comparisons with other populations to identify the limiting factors that are broadly important. The high density of wild dogs in Selous (40 adults/1000 km2) is associated with weak competition from lions and spotted hyenas. Across ecosystems, population density is negatively related to the intensity of interference competition with larger carnivores. Predation by lions and hyenas accounted for 13% of known-cause deaths in Selous and 33–50% in other populations. Intraspecific competition caused 69% of known-cause deaths in Selous, through infanticide and fights between packs, although most of the victims were juveniles with low reproductive value. Infectious diseases had little apparent impact in Selous (4% of deaths) or Kruger National Park (5%), but did play a role in the extinction of a small population in Serengeti. Infectious diseases and competition will generally interact because competitors harbor and transmit the diseases that affect wild dogs. Human activities caused 12% of deaths in Selous, even though it is large (43 000 km2) and does not border large human or livestock populations. Humans were the major agent of mortality in some populations. Foraging success varied little across ecosystems and was not apparently limiting. Mitochondrial DNA (mtDNA) genotypes revealed clinal variation between Selous and distant populations (rather than geographically isolated subspecies, as previously suggested). All wild dog populations have a genetically effective size (Ne) less than 500, so gene flow is necessary to maintain genetic diversity within populations.

Data on mating systems suggest that mate choice and dominance advantages by mallard (Anas platyrhynchos) males are not sufficient to explain declines in American black ducks (Anas rubripes). Courtship and pairing of mallards and American black ducks overwintering at a site on the Chesapeake Bay were studied from 1976–1993, during October–March. Mallards declined relative to American black ducks during this period at the study site. Courtship groups and pairs (one exception) consisted of conspecific individuals. Mallards and American black ducks segregated when courting but not when resting. Hybrid males joined courting groups of either species but did not pair successfully with either parental species. Handraised American black ducks hatched from eggs, imprinted on humans, and fledged at the study site, paired with American black ducks even though they were initially the rarer species. Handraised American black ducks avoided pairing with siblings. American black ducks and mallards pair assortatively and hybrids are selected against on the Chesapeake Bay. American black ducks may be declining due to human disturbance rather than due to direct interactions with mallards. Mallards may be increasing because they tolerate human disturbance and through direct release by humans into the American black duck's breeding range.

Branching (birth–death) models are used to project the time to extinction for bird and mammal orders. While such projections are very coarse, they provide information on how long fundamental units of biodiversity, as represented by such higher taxa as orders, will persist at specified rates of species extinction. The results of a basic decay model indicate that, if all threatened species in each order go extinct within the next 100 years, and this species extinction rate continues indefinitely, then half the species in most orders will disappear in a few hundred years or less. This result is robust and is in agreement with other estimates. A more detailed branching model indicates that most bird and mammal orders will become 100% extinct in a few thousand years if current extinction trends are extrapolated. This projection is also relatively robust, as it is consistently produced using a number of different methods and estimates of future species extinction rates. Mammal orders generally have substantially shorter half-lives and time to 100% extinction than bird orders because of a combination of fewer species per order and higher species extinction rates.

A serious concern with the increasing use of translocation and reintroduction in animal conservation programs is the potential for disease transmission between captive and free-ranging populations. As part of an experimental headstarting program, 45 juvenile Cuban iguanas, Cyclura nubila, were artificially incubated, maintained in captivity for six to 18 months, and subsequently released into natural areas on the US Naval Base at Guantánamo Bay, Cuba. Prior to release, all animals underwent physical examinations, hematological analyses, plasma biochemical determinations, and blood and fecal parasite screening. Comparable data were collected from free-ranging juveniles to establish normal baseline values. Although all hematological parameters were within expected ranges for healthy reptiles, captive juveniles exhibited higher total leukocyte counts and percent lymphocytes, but lower percent heterophils, than free-ranging juveniles. All biochemical values other than lactate dehydrogenase and creatine phosphokinase were within normal ranges. Although higher than reported in other species, these enzymes did not differ in captive and free-ranging juveniles. Free-ranging juveniles significantly exceeded captive juveniles in levels of potassium, alkaline phosphatase, lactate dehydrogenase, total protein, cholesterol and triglycerides, whereas the reverse was true for carbon dioxide and glucose. Although free-ranging juveniles exhibited oxyurids and coccidian oocysts in their feces, captive juveniles were negative for the presence of these parasites. Electron microscopy confirmed that a high percentage of both captive and free-ranging juveniles possessed erythrocytes infected with the piroplasm Sauroplasma. Implications of these results for successful repatriation of captive-reared iguanas are discussed.

Thirty-eight captive-born suni (Neotragus moschatus) had chromosomal complements of 2n = 52–56 (fn = 60). Variation in diploid number was the result of two centric fusion polymorphisms: a 4;19 fusion and a putative 18;22 fusion. Specimens that were descendants of wild-caught N. m. akeleyi and N. m. zuluensis were 2n = 52 and 56, respectively, but 2n = 53, 54, and 55 cytotypes were probably the result of hybridization in captivity between the two subspecies. Although populations of suni from different geographic regions are phenotypically indistinguishable, cytogenetic differences between N. m. akeleyi and N. m. zuluensis indicate that they should be recognized as distinct management units. Chromosomal variation among our panel of captive-born specimens and evidence of higher perinatal mortality in supposed hybrid cytotypes suggest that these two subspecies be managed as separate populations, particularly with regard to captive breeding, reintroductions, and animal translocations. Insofar as our findings are restricted to the captive population, the cytogenetics of natural populations of suni should be investigated to determine if indeed N. m. akeleyi and N. m. zuluensis have fixed chromosomal differences or if the centric fusion polymorphisms found in captive animals also occur in wild suni.

The Cape Sable seaside-sparrow (Ammodramus maritimus mirabilis) has disappeared from its only known breeding areas episodically since its discovery early this century. Systematic surveys across its range in the southern Everglades find the sparrow's range to be fragmented into six subpopulations. The sparrow population decreased by 58% between 1992 and 1995, with the near extinction of the western half of the population and the temporary local extinction of some eastern populations. Other similar grassland sparrows have populations that vary considerably from year to year. Yet the decline in the western subpopulation and the local extinction of some of the peripheral populations cannot be explained by natural variability alone. Hurricane Andrew passed over several subpopulations prior to the particularly poor year of 1993. However, the geographical and temporal patterns of subpopulation decline are not consistent with what would be expected following a hurricane. Frequent fires prevent successful breeding as does flooding during the breeding season. Better management can prevent frequent fires and episodic flooding. However, the long-term survival of the sparrow depends on managing the unanticipated risks that attend its small, fragmented population.

A long-term systematic approach to planning the reintroduction of Persian fallow deer (Dama dama mesopotamica) and Arabian oryx (Oryx leucoryx) in Israel is presented. The reintroductions rely on local breeding-cores that are at their holding capacity of 150 deer and 80 oryx. The approach is based on three elements: (1) maximizing the number of animals that can be withdrawn from a permanent breeding core for the purpose of reintroduction using ‘maximum sustained yield’ (MSY) techniques; (2) determining a priori, using rules-of-thumb (such as IUCN Red List Categories), preliminary criteria for project completion; and (3) estimating the time it would take the reintroduced populations to meet the criteria for project completion. I used Monte Carlo Leslie matrix growth models to determine MSY and to project the growth of the reintroduced population. Based on these simulations, the MSY for the fallow deer breeding-core is 15 adult females in the first year and 12 adult females/year thereafter. The oryx breeding-core can yield 12 adult females during the first year and 16 adult females every third year thereafter. Project completion was preliminarily set to a wild population of 250 adult deer and 100 adult oryx. The simulations predict that it will take 8–11 years to complete the fallow deer reintroduction and 6–10 years to complete the oryx reintroduction. Post-release monitoring will help improve the data used in the model and permit re-assessment of the criteria for project completion.

This study presents the testing of two unsupervised classification methods for their ability to accurately identify unknown individual tigers, Panthera tigris, and snow leopards, Panthera uncia, from their footprints. A neural-network based method, the Kohonen self-organizing map (SOM), and a Bayesian method, AutoClass, were assessed using hind footprints taken from captive animals under standardized conditions. AutoClass successfully discriminated individuals of both species from their footprints. Classification accuracy was greatest for tigers, with more misclassification of individuals occurring for snow leopards. Examination of variable influence on class formations failed to identify consistently influential measurements for either species. The self-organizing map did not provide accurate classification of individuals for either species. Results were not substantially improved by altering map dimensions nor by using principal components derived from the original data. The interpretation of resulting classifications and the importance of using such techniques in the study of wild animal populations are discussed. The need for further testing in the field is highlighted.

As the human population increases, wildlife is becoming restricted to protected remnants of ecosystems with boundaries that limit dispersal. The effect on large herbivores generally is an increase in population density. We investigated the relationship between population density and reproduction in white rhinos (Ceratotherium simum) in Matobo National Park, Zimbabwe. Two lines of evidence were examined: (1) a contrast in reproduction between a high-density and a low-density population; and (2) a longitudinal analysis of changes in reproductive parameters of a fenced population as density increased by >200%. As density increased within the fenced area, the rates of population growth and recruitment of calves decreased, and the age at first reproduction for females increased significantly. Females in the low-density population produced their first calves at significantly younger ages than those in the high-density population. Loss of body condition was related to both population density and female reproductive status. Because most African rhinos exist in relatively small reserves, an understanding of the implications of restricted dispersal and increased population density on their demography is critical to their conservation in situ. Managers need to consider trade-offs between enhanced safety from poaching and density-dependent effects on reproduction in developing conservation strategies for rhinos and other rare, large species confined to reserve systems.

As effective population size (Ne) decreases, genetic factors may become relatively important to a population's or species' persistence. Conservation biologists should be aware of anything that can potentially cause a sudden reduction in Ne. I used simple models to illustrate how certain types of female mating preferences combined with certain types of male traits may lead to a sudden and substantial decrease in Ne. Specifically, if and when there is a sudden ‘downward’ shift in the expression of condition-dependent male traits, females using fixed-threshold mate choice criteria might find fewer acceptable males. While mechanisms of female choice remain elusive, a variety of sexually selected traits may be condition dependent. Because the expression of condition-dependent traits is likely to be impacted by natural or human-induced environmental changes, behavioral and conservation biologists should pay special attention to them around the mating season. Armed with knowledge of condition-dependent male traits, it may be possible to minimize the impact on condition-dependent traits while planning translocations or reintroductions.

The legally endangered Cape Sable seaside-sparrow (Ammodramus maritimus mirabilis) is restricted to short-hydroperiod, marl prairies within Florida's Everglades National Park and Big Cypress National Preserve. Marl prairies are typified by dense, mixed stands of graminoid species usually below 1 m in height, naturally inundated by freshwater for 3–7 months annually. Water levels affect the birds directly, by flooding their nests, and indirectly by altering the habitat on which they depend. Managed redistribution of water flows flooded nearly half of the sparrow's geographical range during several consecutive breeding seasons starting in 1993. Furthermore, these high water levels rapidly changed plant communities, so jeopardizing the sparrow's survival by reducing the availability of nesting habitat.

The yellow-eyed penguin is a threatened species endemic to New Zealand and its subantarctic islands. Survival and fledging success vary from year to year partly in response to changing food availability. Mortality in ‘poor food’ years may potentially be reduced if adults are allowed to rear only one of their two chicks. Conservation managers have therefore deliberately reduced broods to one in some recent breeding seasons, but the merits of this policy are controversial. We investigated, by simulation modelling, the conditions under which a policy of artificial brood reduction would enhance population growth. Food supply may be difficult to predict from early-season indicators so we also considered the effect of forecasting errors. Artificial brood reduction can increase the population growth rate, even in the presence of moderate forecasting errors, given a large enough cost of breeding. However, field studies suggest that the required cost of breeding is unrealistically large and the policy is unlikely to be a useful management tool for yellow-eyed penguins.

We used a demographic model to calculate a series of annual Ne/Nestimates ((Ne/N)S) for a population of the endangered San Joaquin kit fox (Vulpes macrotis mutica) and to identify the demographic parameters explaining significant portions of the variation in (Ne/N)S estimates. Demographic data were collected between 1981 and 1995 from adult kit foxes located on the Naval Petroleum Reserves in California. Demographic parameters were estimated by determining the sex of captured adult foxes and monitoring the survival and reproduction of adult foxes fitted with radiocollars. Individual demographic parameters explaining significant portions (P < 0.10) of the variation in (Ne/N)S estimates was determined using forward stepwise multiple regression. Estimates of (Ne/N)S were highly variable, ranging from 0.22 to 1.15, (x = 0.67, SEM = 0.07, n = 14), with a harmonic mean of 0.55. Forward stepwise multiple regression analysis indicated that mean annual female survival (P = 0.002) and mean annual female reproductive success (P = 0.004) explained significant portions of the variation in estimates of (Ne/N)S, while mean annual sex ratio (P = 0.159), mean annual litter size (P = 0.406) and mean annual male survival (P = 0.922) did not. Long-term kit fox conservation strategies will probably have to account for wide variation in (Ne/N)S ratios and focus on maintaining or expanding the size and connectivity of populations.

As large-bodied mammals become restricted to progressively smaller fragments of former habitat, competitive interactions and interspecies aggression are likely to intensify. Data on the outcomes of 159 encounters between endangered African pachyderms revealed that: (1) female elephants (Loxodonta africana) dominated both sexes of black rhinos (Diceros bicornis); and (2) rhino males but not females displaced elephant bulls. The results of an additional 127 interactions involving pachyderms and 12 additional mammals ranging in size from cheetahs (Acinonyx jubatus) to giraffe (Giraffa camelopardalis) indicates that females of either pachyderm deny immediate access to limited resources. Although the evolution of gender-specific asymmetries in interspecific dominance has received little formal study, it may best be explained by understanding patterns of parental investment; however, from a conservation perspective, one consequence of size-related dominance is that with continued containment of elephants and rhinos in managed reserves, the most handicapped species are likely to be the smaller ones.

Conservation of tropical forests requires an understanding of the seasonal patterns of abundance and distribution of important seed dispersers. In the forests of Central Africa, three species of hornbills in the genus Ceratogymna (Aves: Bucerotidae) provide dispersal for over 50 species of trees and lianas, yet their ecology is poorly known. We present the first empirical evidence for resource tracking and large-scale movements by two of these species, which were previously considered resident. Hornbill numbers and fruit production were estimated over a one-year period in the Dja Reserve, Cameroon. Monthly abundances of C. atrata and C. cylindricus varied four- and 12-fold, respectively, and were predicted by community fruit availability as measured by fruitfall on a 4.3 km trail. In contrast, C. fistulator abundances varied little and were not related to fruit availability. Synchronous population fluctuations in sites 22 km distant were observed for atrata and cylindricus, but not for fistulator. Together, these results indicate that atrata and cylindricus populations track fruit resources via seasonal emigrations, while the fistulator population appears to be relatively sedentary. Comparisons of hornbill densities in primary and secondary forests suggest that they are important dispersers in both habitats, and will likely play larger roles in central African forest regeneration as more vulnerable seed dispersers are removed by hunting. If large seasonal movements of hornbills turn out to be a general phenomenon, effective management of central African forest reserves will require greater emphasis on reserve connectivity and on seasonal and spatial patterns of fruit production.