Island Fox Urocyon Littoralis Research Articles

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.

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.

Does litter size variation affect models of terrestrial carnivore extinction risk and management?

BackgroundIndividual variation in both survival and reproduction has the potential to influence extinction risk. Especially for rare or threatened species, reliable population models should adequately incorporate demographic uncertainty. Here, we focus on an important form of demographic stochasticity: variation in litter sizes. We use terrestrial carnivores as an example taxon, as they are frequently threatened or of economic importance. Since data on intraspecific litter size variation are often sparse, it is unclear what probability distribution should be used to describe the pattern of litter size variation for multiparous carnivores.Methodology/Principal FindingsWe used litter size data on 32 terrestrial carnivore species to test the fit of 12 probability distributions. The influence of these distributions on quasi-extinction probabilities and the probability of successful disease control was then examined for three canid species – the island fox Urocyon littoralis, the red fox Vulpes vulpes, and the African wild dog Lycaon pictus. Best fitting probability distributions differed among the carnivores examined. However, the discretised normal distribution provided the best fit for the majority of species, because variation among litter-sizes was often small. Importantly, however, the outcomes of demographic models were generally robust to the distribution used.Conclusion/SignificanceThese results provide reassurance for those using demographic modelling for the management of less studied carnivores in which litter size variation is estimated using data from species with similar reproductive attributes.

Reducing nontarget recaptures of an endangered predator using conditioned aversion and reward removal

Summary1. Live‐trapping is a fundamental tool in the study of wildlife species and populations. Capture of nontarget species is an inherent side‐effect of trapping animals that is inefficient and potentially detrimental to individuals and populations. Reducing recapture of nontarget species will increase the efficiency of long‐term studies and projects, and minimize unwanted impacts.2. During the initial stages of a 3‐year feral cat Felis catus control programme on San Clemente Island, California, USA, we experienced high recapture rates of nontarget endangered San Clemente Island foxes Urocyon littoralis clementae, impacting project efficiency and potentially foxes.3. We investigated whether we could modify our baiting strategy to reduce fox recaptures using behavioural modification techniques, while simultaneously maintaining the ability to capture feral cats. We tested two strategies, aversive conditioning and reward removal, to reduce fox recapture rates.4. Using lithium chloride (LC) as an aversive agent, we reduced fox recapture rates more than 10 times compared with rates using control bait. Using the reward removal technique, we reduced fox recapture rates almost 20 times compared with control baits. Neither behavioural modification technique deterred cats from entering traps, and our results suggest that by reducing fox recaptures, we improved our ability to capture cats.5. Synthesis and applications. These novel baiting strategies have wide applicability in wildlife research and management. The efficiency of long‐term monitoring or control programmes may be enhanced by discouraging recapture of ‘trap happy’ animals. Potential impacts to threatened species confined in traps could be minimized by reducing recaptures. Sampling of rare species in biodiversity studies could be improved by reducing recapture of competitively superior or numerically dominant species.

The importance of reproductive management and monitoring in canid husbandry and endangered‐species recovery

The importance of captive breeding has evolved as zoos themselves have evolved. Beyond allowing captive populations to be self‐sustaining, zoos can contribute to species recovery and reintroduction by improving reproductive rates and developing monitoring techniques that provide data critical to understanding reproductive processes. Several threatened canid species have recently been saved through captive‐breeding efforts in partnership with reintroduction programmes. Two of those, the Mexican grey wolf Canis lupus baileyi and the Island fox Urocyon littoralis, provide case studies. For both species, data generated during monitoring revealed important basic features of their biology and also provided critical information to managers that could be used to enhance reproductive rates. Both species are also part of reintroduction programmes that exemplify successful partnerships between the United States Fish and Wildlife Service and North American zoos.

Cooperative conservation: zoos and in situ captive breeding for endangered Island fox Urocyon littoralis ssp

Successful captive breeding of endangered Island foxes, which essentially saved San Miguel Island foxes Urocyon littoralis littoralis and Santa Rosa Island foxes Urocyon littoralis santarosae from extinction, was facilitated by collaboration between land‐management agencies and the zoo community. Although the captive breeding was conducted in situ (on‐island) by the agencies, participating zoos offered skill sets and experience that the agencies lacked. Zoos contributed significantly to the development of Island fox husbandry guidelines, genetic management of captive foxes through a studbook, provision of adequate veterinary care and conservation education. Such proactive collaboration may become increasingly necessary for species conservation, given likely impacts to species from global climate change and human population growth.

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.

Possible contemporary evolution in an endangered species, the Santa Cruz Island fox

AbstractAn ability to mount rapid evolutionary responses to environmental change may be necessary for species persistence in a human‐dominated world. We present evidence of the possibility of such contemporary evolution in the anti‐predator behaviour of the critically endangered Santa Cruz Island fox Urocyon littoralis. In 1994, golden eagles colonized Santa Cruz Island, CA and devastated the predator‐naïve, endemic island fox population by 95% within 10 years. In 1992, just before the arrival of golden eagles, foxes showed substantial diurnal activity, but diurnal activity was 37.0% lower in 2003–2007, after golden eagle colonization; concurrently, overall activity declined and nocturnal activity increased. Moreover, on nearby Santa Catalina Island, where golden eagles were absent but where the fox population recently crashed due to a disease epidemic, remaining foxes were significantly more diurnally active than were those on Santa Cruz Island. The weight of evidence suggests that the change in activity pattern was a response to predation, not to low population density, and that this was probably a heritable rather than a learned behavioural trait. This behavioural change may allow for prolonged island fox persistence, but also potentially represents a loss of behavioural diversity in fox populations.

Using pregnancy rates and perinatal mortality to evaluate the success of recovery strategies for endangered island foxes

AbstractFollowing a dramatic population decline in 1999, captive‐breeding and translocation programs were initiated to recover the Santa Catalina Island fox Urocyon littoralis. Neonatal losses during the first year of captive breeding raised concerns, but little information was available on which to base reproductive expectations in captivity, and pregnancy rates and pup mortality had not been assessed in free‐ranging foxes. In 2002 and 2003 we evaluated the relative contributions of captive breeding and translocation to population recovery by comparing pregnancy rates and perinatal mortality in free‐ranging and captive Santa Catalina Island foxes, and by comparing pregnancy rates and perinatal mortality were also compared between resident free‐ranging foxes and foxes that had been captive bred and released, or translocated as juveniles. Pregnancy rates and fetal number were determined using ultrasound. Free‐ranging pregnant foxes were followed via radiotelemetry, and a combination of camera‐traps, observation and targeted trapping was used to determine how many pups survived to weaning. Video cameras and observations were used to determine the weaning success for captive foxes. The adult pregnancy rate for free‐ranging foxes (95.0%) was higher than for adult captive foxes (47.6%; P=0.003). Perinatal mortality for pups born to free‐ranging mothers (43.2%) was higher than for pups born to captive mothers (15.0%, P=0.055). Adult pregnancy rates and perinatal mortality were 100 and 25.0% for translocated and captive‐bred foxes combined, and 92.3 and 53.6% for resident wild foxes. The average weaned litter size (±standard deviation) for free‐ranging foxes (1.8±0.6) was similar to that for captive foxes (2.1±0.4). Successful pup production by translocated and captive‐bred foxes supports the utility of these strategies to recover island foxes. Our approach, integrating veterinary and field biology techniques to assess the contributions of different management strategies to population recovery, can be utilized for other endangered species.

The behavioural ecology of the island fox (Urocyon littoralis)

AbstractInsular populations typically occur at higher densities, have higher survivorship, reduced fecundity, decreased dispersal, and reduced aggression compared to their mainland counterparts. Insularity may also affect mating system and genetic population structure. However, these factors have not been examined simultaneously in any island vertebrate. Here we report on the ecological, behavioural and genetic characteristics of a small carnivore, the island fox Urocyon littoralis, from Fraser Point, Santa Cruz Island, California. Dispersal distances in island foxes are very low (mean 1.39 km, sd 1.26, range 0.16–3.58 km, n=8). Home‐range size is one of the smallest (mean annual home range=0.55 km2, sd 0.2, n= 14) and density is nearly the highest recorded for any canid species (2.4–15.9 foxes/km2). Similar to other fox species, island foxes are distributed as mated pairs that maintain discrete territories. Overlap among mated pairs was always high (mean 0.85, sd 0.05), while overlap among neighbours (mean 0.11, sd 0.13), regardless of sex, was low. Despite this high degree of territoriality, island foxes are not strictly monogamous. Four of 16 offspring whose parents were identified by paternity analysis were a result of extra‐pair fertilizations. Mated pairs were unrelated, however, suggesting inbreeding avoidance. Substantial population differentiation was found between the Fraser Point subpopulation and one only 13 km away (Fst= 0.11). We suggest that the primary effect of finite island area is to limit dispersal, which then influences the demography, behaviour and genetic structure of island fox populations.