Feral Pigs Sus Scrofa Research Articles

Effectiveness of signs of activity as relative abundance indices for wild boar

Population growth in wild boars and feral pigs Sus scrofa has negative environmental and economic implications worldwide. Accordingly, it is necessary to monitor population trends for appropriate management. Despite the potential for bias, relative abundance indices based on signs of activity have the potential to be practical, low-cost monitoring tools for data collection at a local scale and over large areas. However, few studies have examined the effectiveness of specific signs as measures of relative wild boar abundance in comparison with reliable density estimates. In this study, we examined whether three activity signs (digging marks, rubbing marks and fecal pellet groups) could be used as relative abundance indices for wild boar. In particular, we conducted transect surveys for signs of activity as well as camera trap surveys from September 2017 to January 2018 at six sites in Hyogo Prefecture and eight sites in Chiba Prefecture, Japan. We modeled the relations between the number of activity signs and wild boar densities or abundances estimated from camera trap data in a hierarchical framework. Fecal pellet counts is a well-established method for estimating the abundance of herbivores, including wild boar; however, we found few fecal pellet groups in our study area, and the counts were not related to wild boar densities. Instead, we found that digging marks were strongly associated with estimates of wild boar density. Although fluctuations in the number of digging marks may be affected by factors other than boar density, including environmental conditions and seasonality, our results suggest that digging marks are an effective relative abundance index for evaluations of the spatial patterns of wild boar in Japan.

Community reorganization revealed by exploring shifts in the diet of an apex predator, the Golden Eagle Aquila chrysaetos, with stable isotopes and prey remains

Golden Eagles Aquila chrysaetos colonized the northern California Channel Islands, an archipelago located off the coast of southern California, USA, in the early 1990s, owing in part to the presence of Feral Pigs Sus scrofa. Eagles preyed on piglets and on the endemic Island Fox Urocyon littoralis, driving three endemic subspecies of the Island Fox (U. l. santacruzae, U. l. santarosae and U. l. littoralis) toward extirpation. Using stable isotopes (δ13C and δ15N) measured from feathers and blood of Golden Eagles and from meat and bone of their prey, along with the proportion of prey consumed estimated from nest excavations as informative priors, we show that shifts in Eagle isotopic signatures tracked community reorganization: when pigs and foxes were abundant, Eagles consumed them in higher proportions than other prey; when foxes became scarce owing to Eagle predation, Eagle diet shifted toward pigs, but also diversified to include Common Ravens Corvus corax and seabirds (Larus spp. and Phalacrocorax spp.); and finally, after pigs were eradicated and 35 Golden Eagles had been captured and removed from Santa Cruz Island, a lone remaining pair of Eagles reversed their diet to include more foxes. Our findings reveal that shifts in stable isotope signatures from tissues of an apex predator can be used as a general proxy to monitor changes in the prey community; however, if sample sizes are small, informative priors are both essential and overwhelmingly influential, and changes in abundance of preferred prey may mask or fail to reveal changes in less preferred prey. Given that apex predators are at the top of trophic hierarchies, that they are often important drivers of community structure and that they sample prey continuously from their community, isotopic signatures of their tissues may be useful for monitoring community change.

Are camera surveys useful for assessing recruitment in white‐tailed deer?

Camera surveys commonly are used by managers and hunters to estimate white‐tailed deer Odocoileus virginianus density and demographic rates. Though studies have documented biases and inaccuracies in the camera survey methodology, camera traps remain popular due to ease of use, cost‐effectiveness, and ability to survey large areas. Because recruitment is a key parameter in ungulate population dynamics, there is a growing need to test the effectiveness of camera surveys for assessing fawn recruitment. At Savannah River Site, South Carolina, we used six years of camera‐based recruitment estimates (i.e. fawn:doe ratio) to predict concurrently collected annual radiotag‐based survival estimates. The coefficient of determination (R2) was 0.445, indicating some support for the viability of cameras to reflect recruitment. We added two years of data from Fort Bragg Military Installation, North Carolina, which improved R2 to 0.621 without accounting for site‐specific variability. Also, we evaluated the correlation between year‐to‐year changes in recruitment and survival using the Savannah River Site data; R2 was 0.758, suggesting that camera‐based recruitment could be useful as an indicator of the trend in survival. Because so few researchers concurrently estimate survival and camera‐based recruitment, examining this relationship at larger spatial scales while controlling for numerous confounding variables remains difficult. Future research should test the validity of our results from other areas with varying deer and camera densities, as site (e.g. presence of feral pigs Sus scrofa) and demographic (e.g. fawn age at time of camera survey) parameters may have a large influence on detectability. Until such biases are fully quantified, we urge researchers and managers to use caution when advocating the use of camera‐based recruitment estimates.

Status of the Endangered Yellow Chat Epthianura crocea tunneyi on the western South Alligator River floodplain, Kakadu National Park

The current status of the Endangered Yellow Chat Alligator Rivers subspecies Epthianura crocea tunneyi is poorly known. A survey of Kakadu National Park floodplains, Northern Territory, in 2004 identified the western floodplain of the South Alligator River as a key population area. To provide preliminary information on the status of the subspecies in Kakadu National Park, this floodplain was intensively surveyed over a 4-day period in September 2014 and compared with the 2004 survey, which was undertaken at a similar time of year (late dry season: October–November). Despite covering considerable areas of floodplain habitat over nearly 40 hours of surveying, Yellow Chats were recorded in only one area in 2014; 27 Yellow Chats from nine observations were recorded over 2 days, with a minimum number of 17 individual birds (16 adult and 1 juvenile) observed. This compared with a total of 65 Yellow Chats from 2 days of surveying in 2004, clustered around five areas of the western floodplain of the South Alligator River. Habitat in 2014 comprised predominantly dry floodplain lagoon, consistent with previous surveys. Feral animals (in particular Feral Pigs Sus scrofa ) were regularly observed throughout the surveys, as was significant feral-animal damage to wet floodplain areas. Although these results suggest a possible decline on the western South Alligator River floodplain over a 10-year period, a comprehensive survey is required of all floodplains within the subspecies’ range to assess overall population status. This could inform the establishment of annual monitoring sites in order to evaluate long-term population trends, essential data for management of threatened species.

An irruption interrupted: eradication of wild turkeys Meleagris gallopavo from Santa Cruz Island, California

AbstractEradication of introduced species is often necessary to conserve native biota on islands. Seven wild turkeys Meleagris gallopavo were introduced to Santa Cruz Island, California, in 1975 and the population began to irrupt in the early 2000s. Turkeys posed a variety of threats to native species, including that they could replace the previously eradicated population of feral pigs Sus scrofa as a prey subsidy for golden eagles Aquila chrysaetos, which through incidental predation had driven three subspecies of island fox Urocyon littoralis to near extinction. We implemented a four-phase programme to eradicate the turkey population, based on general principles for eradication efforts. For example, we focused on preventing individual turkeys from becoming aware of our methods, which increased the likelihood we would be able to detect and dispatch all of the birds. Leveraging the tendency of turkeys to aggregate during winter, we used baited drop nets, precision shooting, and monitoring of surgically sterilized, radio-telemetered ‘Judas turkeys’ to eliminate the population. We estimate the population comprised 310 individuals when the project began in 2006 and that the last bird died in December 2012. Methods used in this project could be applied to other alien bird eradication programmes, of which there are few examples in the scientific literature.

Impacts and management of wild pigs Sus scrofa in Australia

Abstract Globally, wild or feral pigs Sus scrofa are a widespread and important pest. Mitigation of their impacts requires a sound understanding of those impacts and the benefits and limitations of different management approaches. Here, we review published and unpublished studies to provide a synopsis of contemporary understanding of wild pig impacts and management in Australia, and to identify important shortcomings. Wild pigs can have important impacts on biodiversity values, ecosystem functioning and agricultural production. However, many of these impacts remain poorly described, and therefore, difficult to manage effectively. Many impacts are highly variable, and innovative experimental and analytical approaches may be necessary to elucidate them. Most contemporary management programmes use lethal techniques to attempt to reduce pig densities, but it is often unclear how effective they are at reducing damage. We conclude that greater integration of experimental approaches into wild pig management programmes is necessary to improve our understanding of wild pig impacts, and our ability to manage those impacts effectively and efficiently.

Fluoroacetate-bearing vegetation: can it reduce the impact of exotic mammals on wildlife conservation?

THERE is no doubt that fluoroacetate-bearing vegetation (also known as poison peas) has had a profound effect on the evolution and persistence of Western Australian biota. Most of these plants belong to the genus Gastrolobium, and most are found in the south-west corner of Western Australia (Gardner and Bennetts 1956; Aplin 1971; Twigg and King 1991). The toxic principle of these plants, fluoroacetate, is also manufactured synthetically as 1080 (sodium fluoroacetate) for Australiawide control of vertebrate pests, such as rabbits Oryctolagus cuniculus, foxes Vulpes vulpes, wild dogs Canis lupus familiaris and feral Pigs Sus scrofa (Twigg and King 1991). Because of their co-evolution with fluoroacetate-bearing vegetation, many native animals in Western Australia have developed varying levels of tolerance to this highly toxic compound. In contrast, introduced mammals are generally highly sensitive to fluoroacetate. Although it is not a prerequisite for safe and effective pest control programmes with 1080, the toxicity differential between native and introduced animals provides an additional “safety net” when using 1080 products in Western Australia.

Invasive species and bushmeat hunting contributing to wildlife conservation: the case of feral pigs in a Neotropical wetland

AbstractAn unusual combination of two major conservation threats, invasive species and bushmeat hunting, has had a positive outcome for wildlife conservation in the Brazilian Pantanal. The Pantanal is a wetland and one of the few non-protected areas in the Neotropics where people live but rarely hunt native wildlife. To understand why wildlife hunting is not a major conservation issue in the Pantanal an exploratory survey, semi-structured interviews, skull collection and tooth wear analysis of feral pig Sus scrofa, white-lipped peccary Tayassu pecari and collared peccary Pecari tajacu were conducted, and hunting registers distributed, in the central region of the Pantanal. The results showed that feral pigs are the main hunting target. Feral pigs are effectively acting as a replacement species for hunting of native wildlife because the pigs provide a constant, culturally acceptable, readily available and free source of meat and oil to remote ranches. We cannot evaluate, however, if the buffer from hunting that feral pigs provide to native wildlife outweigh this species’ potential negative ecological impacts.

Prevalence of Tree Regeneration by Sprouting and Seeding Along a Rainfall Gradient in Hawai'i

ABSTRACTDrought stress in tropical dry forests is thought to result in greater asexual regeneration via vegetative sprouting (e.g., basal, root, and branch layering) than occurs in moister tropical forests. We tested this hypothesis by examining the prevalence of tree sprouting and seeding in tropical forests located along a rainfall gradient on the island of Hawai'i. Additionally, we examined the potential for novel disturbance, feral pig Sus scrofa rooting and trampling, to alter patterns in tree regeneration mode. We found greater sprouting (in terms of relative density and basal area) in dry forests than in mesic and wet forests, supporting the hypothesis. We also found that feral pig disturbance is negatively correlated with the relative density and basal area of seedlings in wet forests, but is positively correlated with the relative importance of sprouting, and the richness and diversity of sprouting species. Our results suggest rainfall regimes may be an important factor controlling broad‐scale patterns in tree regeneration mode, and that exotic ungulates can significantly modify such patterns with potential consequences for the structure and dynamics of tree populations and communities.

Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig

BackgroundInvasive species are recognized as a primary driver of native species endangerment and their removal is often a key component of a conservation strategy. Removing invasive species is not always a straightforward task, however, especially when they interact with other species in complex ways to negatively influence native species. Because unintended consequences may arise if all invasive species cannot be removed simultaneously, the order of their removal is of paramount importance to ecological restoration. In the mid-1990s, three subspecies of the island fox Urocyon littoralis were driven to near extinction on the northern California Channel Islands owing to heightened predation by golden eagles Aquila chrysaetos. Eagles were lured to the islands by an abundant supply of feral pigs Sus scrofa and through the process of apparent competition pigs indirectly facilitated the decline in foxes. As a consequence, both pigs and eagles had to be removed to recover the critically endangered fox. Complete removal of pigs was problematic: removing pigs first could force eagles to concentrate on the remaining foxes, increasing their probability of extinction. Removing eagles first was difficult: eagles are not easily captured and lethal removal was politically distasteful.Methodology/Principal FindingsUsing prey remains collected from eagle nests both before and after the eradication of pigs, we show that one pair of eagles that eluded capture did indeed focus more on foxes. These results support the premise that if the threat of eagle predation had not been mitigated prior to pig removal, fox extinction would have been a more likely outcome.Conclusions/SignificanceIf complete eradication of all interacting invasive species is not possible, the order in which they are removed requires careful consideration. If overlooked, unexpected consequences may result that could impede restoration.

New perspectives on harvesting as one driver of ecosystem dynamics

New perspectives on harvesting as one driver of ecosystem dynamics

Molecular techniques, wildlife management and the importance of genetic population structure and dispersal: a case study with feral pigs

Summary Understanding the spatial structure of populations is important in developing effective management strategies for feral and invasive species, such as feral pigs Sus scrofa. World‐wide, feral pigs can act as ‘triple threat’ pests, impacting upon biodiversity, agricultural production and public health; in Australia they are a significant vertebrate pest. We utilized a molecular approach to investigate the structure of populations of feral pigs in south‐western Australia. These approaches have been underutilized in pest management. Using 14 highly polymorphic microsatellite markers from 276 adult pigs, we identified eight inferred (K = 8) pig populations that would be difficult to define with standard ecological techniques. All populations had moderate heterozygosity (HE = 0·680) and moderate to high levels of differentiation (FST = 0·118; RST = 0·132) between populations. The molecular approach identified feral pig groups that appeared to be acting as a source for reinvasion following control operations. It also identified populations where current control measures were less successful in reducing ‘effective population size’. Additionally, the data indicated that dispersal rates between, but not within, the inferred feral pig populations were relatively low. The potential for the spread of directly transmitted wildlife diseases between the pig populations studied was low. However, under some circumstances, such as within major river catchments, the role of feral pigs in the transmission of endemic or exotic diseases is likely to be high. Synthesis and applications. A molecular‐based approach allowed us to determine the genetic structure and dispersal patterns of a cryptic, destructive and invasive vertebrate pest. Our results indicated that the feral pig populations studied were unlikely to be acting as closed populations and, importantly, it identified where movement between groups was likely to occur. This should lead to more informed decisions for managing the potential risk posed by feral species, such as pigs, in the transmission of wildlife diseases. The suggested technique could help in understanding the dynamics of many other free‐ranging pest animal populations.

The role of introduced mammals and inverse density-dependent predation in the conservation of Hutton's shearwater

This study investigated the impact of stoat Mustela erminea predation on the endangered Hutton's shearwater Puffinus huttoni. Breeding success of Hutton' shearwaters was significantly lower in two seasons of stoat control than in eight seasons with no control: suggesting that natural environmental variation has a greater influence on breeding success than stoat predation. Monitoring Hutton's shearwaters and mainland colonies of sooty shearwaters Puffinus griseus indicated that small colonies suffered higher predation and lower breeding success than large colonies, demonstrating that predation in these two species is inversely density dependent and explaining the low predation rates observed in the very large Hutton's shearwater colonies. The presence of another introduced predator, feral pigs Sus scrofa, within six extinct colonies of Hutton's shearwaters and at the boundaries of the two extant colonies, strongly suggests that this species was responsible for the historic contraction in breeding range. Controlling stoats within the two remaining colonies is unlikely to assist in the conservation of Hutton's shearwater. Conservation efforts would be better spent protecting the two remaining colonies from pigs and in trying to establish new breeding sites.

Abundance and management of Mariana Fruit Bats and feral ungulates on Anatahan, Mariana Islands

A survey of Mariana Fruit Bats Pteropus mariannus and feral ungulates was conducted on Anatahan, Mariana Islands, in July 1995. We estimated that a population of 1 902-2 136 bats persists on the island, based on a combination of direct colony counts, departure counts, and station counts of non-colonial animals. Our data suggest that bat numbers have declined since the last surveys were made in 1983 and 1984. We located seven colonies, which held approximately 85-92% of the total population. Most colonies and foraging animals were associated with native forest or isolated native trees in other habitats. Bats fed on five species of plants, with the fruit of Pandanus tectorius eaten most frequently. Anatahan supports a very large Feral Goat Capra hircus population estimated at roughly 5 000-6 000 animals. Feral Pigs Sus scrofa are less common. Both species cause severe damage to plant communities of the island. We recommend that a legal hunting programme for fruit bats be deferred until 1) population censuses on neighbouring islands are completed and it is determined that bat populations can sustain harvesting, 2) habitat degradation is reversed through the control of feral animals, and 3) illegal hunting is curtailed.

Demography, sociospatial behaviour and genetics of feral pigs (Sus scrofa) in a semi‐arid environment

AbstractWe examined demographics, dispersal, sex‐related behaviour, group structure, and genetic similarities of female feral pigs Sus scrofa on the Chaparral Wildlife Management Area in southern Texas from June 1993 to December 1995. Cumulative and seasonal ranges and core areas were calculated for 18 female pigs representing three distinct sounders. Simultaneous pairs of radio locations were used to assess behavioural associations among pigs, and DNA fingerprinting was used to determine genetic similarity. Behavioural and spatial associations largely corresponded to genetic relationships. Similarity of behavioural dendrograms to genetic dendrograms indicated that genetic relationships of feral pigs played a role in observed population structure. A single discrepancy between genetic and behavioural dendrograms suggested two animals dispersed to an adjacent sounder. Also, one sounder appeared to have been created by fission from a larger, adjacent sounder. Factors that are important keys in understanding the association between genetics and behaviour of feral pigs include dispersal, climate, habitat quality, population densities, and sex‐related behaviour.

Snaring to control feral pigs sus scrofa in a remote Hawaiian rain forest

Feral pig Sus scrofa control in Kipahulu Valley, a remote rain forest in Haleakala National Park, Maui, Hawaiian Islands, has been achieved with snares over a 45-month period. Initial pig densities in fenced management units of 6·2 km 2 and 7·8 km 2 were estimated at 6 animals/km 2 and 14·3 animals/km 2 for the two units, based on population reconstruction from animals killed and aged. During the 45 months of the study, 1978 snares were set, and 1·6 million snare nights were logged. Snare density reached 96/km 2 and 200/km 2 for the two management units by the end of the study. A mean effort of 43 worker hours/pig was used to remove 53 pigs from the upper management unit, and a mean of 7 worker hours/pig to remove 175 animals from the more densely populated lower unit. Pig activity monitoring along transects provided a good measure of control effectiveness until densities of about 1 pig/km 2 were achieved, after which transects became less useful than scouting for determining pig activity.

Reproductive characteristics of feral pigs in New Zealand

Breeding was studied in feral pigs Sus scrofa Linnaeus, 1758 inhabiting the northern part of the South Island, New Zealand. In the sample of 1,117 female pigs 50.4% showed evidence (pregnancy or lactation) that they were breeding. There was no statisticaly significant regional variation in the breeding status of females.

A Model of the Velocity of Advance of Foot and Mouth Disease in Feral Pigs

(1) A diffusion model was used to calculate the minimum velocity of advance of an outbreak of foot and mouth disease (FMD) in feral pigs Sus scrofa in eastern Australia. The rate of contact between feral pigs, the carrying capacity of the environment for feral pigs, and the duration of the latent period in the development of an FMD infection were found to be important factors affecting the velocity of propagation. (2) Two key parameters in the model, the diffusivity and the contact rate, were estimated from data collected during radio-tracking feral pigs in Namadgi National Park in south eastern Australia. In this environment, with a feral pig density of 1 4 km-2, the velocity of propagation of FMD was estimated to be 2 8 km day