Presence Of Squirrels Research Articles

Occurrence of Fox Squirrels Influenced by Fine-Scale Landscape Characteristics on a College Campus.

Urbanization and urban sprawl generally degrade and diminish wildlife habitat, threatening to extirpate local populations. However, certain synanthropic species (e.g., coyotes, white-tailed deer, and squirrels) are able to persist in urban environments and may even occur at greater densities than they do in their natural habitats. Eastern fox squirrels (Sciurus niger) are large tree squirrels that are known to be present in greater densities within urban areas. To determine how landscape characteristics may affect fox squirrel presence, we conducted line-transect surveys along sidewalks on the Texas A&M University-College Station campus to record presence of fox squirrels and nearest tree species. We calculated Jacobs' index of selectivity (D) for use of trees by fox squirrels along the transects. Squirrel density was calculated for all transects and modeled using linear regression with environmental (e.g., tree density) and survey (e.g., transect distance) variables. Fox squirrels preferred only a small number of the available tree species, primarily Quercus and Ulmus species. Observed fox squirrel density significantly increased with time of day, temperature, density of oaks (Quercus spp.), and density of all trees, and decreased with distance and area of the transect. These results suggest that even when urban areas contain suitable habitat, use of urban environments by wildlife is still highly selective and dependent on specific habitat requirements.

Keystone species in an urban environment: Do raptors control the Mexican gray squirrel in Mexico City?

Urbanization has forced animals to respond to novel environments. One of the basic questions in urban ecology is if ecological processes that occur in natural conditions also occur in urban environments. In natural ecosystems, key predators can limit prey abundance and have a widespread effect on trophic levels. Here, we examine a predator-prey interaction in Mexico City, an urban ecosystem where prey can be evaluated in the presence or absence of apex predators. Nearly all original ecosystems in Mexico City have been transformed for human purposes. Many of the green spaces in the city contain populations of the Mexican gray squirrel, a species native to this area. These green spaces are also inhabited by different species of raptors, the most frequent being Harris's hawk, Cooper's hawk, and sharp-shinned hawk. Little is known about the interactions between raptors and squirrels, particularly how different environmental factors influence this ecological relationship. We do know, however, that raptors prey on squirrels. We predicted that in parks where raptors were present, there would be fewer squirrels than in parks where there were no raptors. We studied the relationship between raptors and squirrels using occupancy models, which also allowed us to evaluate environmental factors that affect the presence of both squirrels and raptors. We also tested if the presence of raptors influenced the occupancy probability of squirrels, and vice versa. Lastly, we estimated the abundance of squirrels in parks, both where raptors were present and where they were absent. Contrary to our predictions, in our first two sampling periods we found a positive relationship between the presence of raptors and squirrel abundance, but this relationship was absent during our second two survey periods, which was due to a decline in squirrel abundance in parks where raptors were present. These results suggest that predator-prey interactions occur in urban settings much as they do under natural conditions, but that other factors unique to urbanization can also impact the abundance of raptors and squirrels. Our findings also suggest that raptors might be an effective means of controlling squirrel populations under some conditions.

Microhabitat use of northern and southern flying squirrels in a recent hybrid zone

Secondary contact of closely related species may lead to hybridization if reproductive isolation is incomplete. We examined the role of habitat use as a factor contributing to reproductive isolation of northern ( Glaucomys sabrinus (Shaw, 1801)) and southern ( Glaucomys volans (Linnaeus, 1758)) flying squirrels in an area of secondary contact in Ontario, Canada. Specifically, we looked at summer microhabitat use within sites of sympatry and allopatry to test for evidence of reinforcement due to diverging habitat use. We also examined differences in broad-scale habitat features at woodlots to determine predictors of species occurrence across sites. We used 18 years (2002–2019) of flying squirrel summer capture data from six sites along a north–south transect and microhabitat data from vegetation surveys conducted during summer 2016. We found microhabitat variables to be weak predictors of trap-level flying squirrel presence, and we found no evidence of divergence in microhabitat use over the 18 years. Further, we found latitude, not broad-scale habitat, was the strongest predictor of site-level flying squirrel occurrence. Overall, our findings suggest that microhabitat-based isolation is not being reinforced between flying squirrels; however, hybridization may be limited to areas where climate and habitat are suitable for both species.

Beaver activity and red squirrel presence predict bird assemblages in boreal Canada

AbstractWetlands and predation in boreal ecosystems play essential roles throughout the breeding season for bird assemblages. We found a positive association of beaver activity and a negative influence of American red squirrels (Tamiasciurus hudsonicus) on bird assemblages. We used a multispecies hierarchical model to investigate whether bird communities differ between two major wetland habitats in boreal Canada: beaver ponds and peatland ponds. In addition to including variables such as forest cover and latitude, we adopted a structural equation model approach to estimate the occupancy of American red squirrels and its potential influence on bird communities. Using automated recording stations deployed at 50 ponds, we detected 96 bird species in 2018 and 2019. Bird species were grouped into four taxonomic guilds according to their habitat successional requirements: early successional species, late successional species, generalists, and wetland species. Beaver ponds harbored higher species richness, a pattern driven primarily by early successional species. The occupancy of almost a quarter of the species was lower in the presence of red squirrels. Late successional species responded positively to the cover of forest surrounding the pond. Our results highlight the value of considering acoustic data of red squirrels to quantify habitat quality in boreal forests. We conclude that beaver activity shapes bird assemblages through modification of their habitat, and that some bird guilds are associated negatively with the presence of American red squirrels.

Dual ecological functions of scatter-hoarding rodents: pollinators and seed dispersers of Mucuna sempervirens (Fabaceae).

Double mutualism, that is, pollination and seed dispersal of the same plant species mediated by the same animal partners, is important but remains elusive in nature. Recently, rodent species were found as key pollinators (i.e. explosive openers) for some Mucuna species in (sub)tropical Asia, but no evidence has shown whether and how these rodents could also act as legitimate seed dispersers via scatter-hoarding for those producing large seeds. Here, my aim was to test the hypothesis that scatter-hoarding rodents could act as double mutualists for both pollination and seed dispersal of the same Mucuna species, that is, Mucuna sempervirens (Fabaceae). Based on camera-trapping survey at 2 locations with or without squirrel presence in the Dujiangyan subtropical forests, Southwest China, 7 mammals and birds were identified as explosive openers for M. sempervirens flowers, but Leopoldamys edwardsi (rats) and Paguma larvata (civets) were the main pollinators at the squirrel-absent site, while Callosciurus erythraeus (squirrels) were the main pollinators at the squirrel-present site. By tracking the fate of individually-tagged seeds over 5 years at each site, I provide the first evidence for seed-eating rodents as legitimate seed dispersers via scatter-hoarding of seeds in this world-wide plant genus, although dispersal services were slightly reduced at squirrel-absent site. More importantly, the dual roles of scatter-hoarding rodents as key pollinators and seed dispersers for the same Mucuna species have shown a clear relationship of double mutualism, and their key services may be essential for population conservation of these Mucuna species in human-disturbed landscapes.

First assessment of ectoparasite prevalence in Apennine populations of Eurasian red squirrel: does habitat fragmentation affect parasite presence?

Although habitat fragmentation is widely reported to affect species survival and distribution, its effect in terms of host-parasite interactions in small mammal communities is poorly studied yet. Using information collected from carcasses of 34 road-kill and two preyed-upon individuals, we present the first comprehensive study dealing with the relationship between habitat fragmentation and the presence of different ectoparasite species infecting a small Sciurus vulgaris population inhabiting the Apennine ridge. We predicted that the probability to find individuals infested by parasites would be lower in highly fragmented areas because of the trade-off effects over both mammal and ectoparasite communities. Our findings showed that the most frequent ectoparasites were the squirrel fleas Ceratophyllus sciurorum and hard ticks Ixodes ricinus. Males showed higher presence of ectoparasites than females, probably because of different behaviour in space use and higher hormone levels, which may compromise host’s resistance to infection. As to the relationship with habitat fragmentation, we did not find support that individuals in highly fragmented areas would be less susceptible to C. sciurorum infestation because of lower red squirrel relative density. The presence of highly suitable habitat patches in fragmented habitats may have favoured the presence of squirrels, hence promoting C. sciurorum transmission among specimens. Similarly, we did not find support that habitat fragmentation would have reduced the likelihood of generalist ectoparasites transmission among squirrels. This finding may be explained by the increasing tolerance of generalist ectoparasites towards habitat fragmentation because of the presence of species (e.g., roe deer Capreolus capreolus) able to better exploit ecotonal areas. We believe that our research provides interesting preliminary results on ectoparasites infesting red squirrels in the Apennine area, and of the potential impact which habitat fragmentation may have on them. Nevertheless, the effect of habitat fragmentation over parasite communities is still poorly considered, and further researches are needed.

Constraints on range expansion of introduced red squirrels (Tamiasciurus hudsonicus) in an island ecosystem

Factors that limit the range expansion of introduced species can offer insights into the basic ecology of these species and inform conservation of associated endemic species. North American red squirrels (Tamiasciurus hudsonicus (Erxleben, 1777)) were recently introduced to the island of Newfoundland, Canada, where they have been implicated in the decline of two endemic bird subspecies. During the summers of 2016 (following conifer masting) and 2017 (following nonmasting), we conducted surveys with 1960 point counts and playback to assess red squirrel distribution and habitat use across a 257 km2 montane landscape in western Newfoundland. We used generalized additive models with stepwise model selection to assess the relationship between land cover and red squirrel occurrence each summer. Red squirrels were most common at low elevations and were not detected at elevations above ∼500 m. Their occurrence was negatively associated with the presence of water, coniferous scrub, and 10- to 30-year-old fir–spruce but positively associated with the presence of 30- to 70-year-old fir–spruce and >70-year-old fir. Red squirrel presence was related to more land cover variables in 2016, after a masting year. The absence of red squirrels from forests at higher elevations apparently resulted from lack of suitable habitat rather than incomplete range expansion. Climate- or silviculture-induced changes in vegetation may alter mid- and upper-elevation habitat suitability.

Woody Cover Mediates Fox and Gray Squirrel Interactions

Human activities are changing the environments that animal communities utilize, altering competition and co-existence dynamics as well as changing species distributions. A global consequence of human activity is increased woody cover, which changes environmental conditions on landscape, local, and fine spatial scales. These multi-scale processes are likely to change species interactions and distributions in unexpected ways. To elucidate these effects, we investigated the co-occurrence of two interacting species in a rapidly changing ecosystem. Eastern fox (Sciurus niger) and gray (S. carolinensis) squirrels occur sympatrically throughout the southeastern United States. We used single-season, two-species occupancy modeling to understand what factors influence competition between the squirrels at three spatial scales. We found evidence that fox and gray squirrels compete at fine scales but not at local and landscape scales. The best model to explain fox and gray squirrel co-occurrence at fine scales was an additive fine scale understory and tree canopy closure model. Increased fine-scale canopy closure correlated with increased fox and gray squirrel occupancy while increased fine-scale understory cover correlated with decreased gray and fox squirrel occupancy. Fox squirrel occupancy probability declined in the presence of gray squirrels. The intensity of interaction was modified by fine-scale canopy cover and understory density. These findings support the hypothesis that species interactions can be an important factor in structuring biotic communities, however the strength of the effect changes across spatial scales. Our results support the importance of considering species interactions at multiple scales when predicting community composition in human modified and managed systems.

Spillover of an alien parasite reduces expression of costly behaviour in native host species.

Understanding the effects of invasive alien species (IAS) on native host-parasite relationships is of importance for enhancing ecological theory and IAS management. When IAS and their parasite(s) invade a guild, the effects of interspecific resource competition and/or parasite-mediated competition can alter existing native host-parasite relationships and the dependent biological traits such as native species' behaviour. We used a natural experiment of populations of native red squirrels Sciurus vulgaris that were colonized by the alien grey squirrel Sciurus carolinensis, comparing repeated measurements of red squirrel parasite infection and personality with those taken in sites where only the native species occurred. We explored two alternative hypotheses: (a) individual differences in personality traits (activity and/or sociability) of native red squirrel positively affect the probability of macroparasite spillover and thus the likelihood to acquire the alien's parasitic helminth Strongyloides robustus; (b) the combined effects of grey squirrel presence and parasite infection result in a reduction of costly personality traits (activity and/or exploration). Using data from 323 arena tests across three experimental (native species and IAS) and three control sites (only native species), we found negative correlations between native species' activity and infection with S. robustus in the sites invaded by the alien species. Activity was also negatively correlated with infection by its native helminth Trypanoxyuris sciuri but only when grey squirrels were present, while in the red-only sites there was no relationship of T. sciuri infection with any of the personality traits. Moreover, individuals that acquired S. robustus during the study reduced their activity after infection, while this was not the case for animals that remained uninfected. Our results show that parasite-mediated competition is costly, reducing activity in individuals of the native species, and altering the native host-native parasite relationships.

Fire impacts on a forest obligate: western gray squirrel response to burn severity

In the southwestern United States, climate change and climate–fire dynamics are affecting the distribution of natural and managed ecosystems. Forest obligate species on sky islands can experience a restriction in range with the increase of destructive forest fires. Using presence/absence data collected by hair tubes, we identified key habitat features that determine the western gray squirrel (Sciurus griseus) distribution on the sky island of the San Bernardino Mountains (California, USA) and determined post-fire differential use of burn severity in a landscape modified by fire. Gray squirrel presence was related to habitat features important for this species’ ecology and behavior, especially those associated with mature forests. The species was detected in areas with a high percentage of conifers that provide both an important food resource and good branches and cavities for nest sites. Gray squirrels occurred in all burn severities but occurred more in low and high severity sites than unburned sites. These results suggest that the gray squirrel can persist after a wildfire and can take advantage of the post-fire habitat structure if a mosaic of burn severities is maintained in the forest.

Interspecific competition affects the expression of personality-traits in natural populations

Competition between animal species can cause niche partitioning and shape an individual’s phenotype, including its behaviour. However, little is known about effects of interspecific competition on personality, the among-individual variation in behaviour that is consistent across different spatial and temporal contexts. We investigated whether alien grey squirrels (Sciurus carolinensis) influenced the expression of personality traits in native red squirrels (Sciurus vulgaris). In Italy, alien grey squirrels replaced native reds through competition for food resources and space, reducing breeding and recruitment in the native species. We compared personality of red squirrels in red-only (no interspecific competition) and red-grey (with interspecific competition) sites, using arena-tests. The trait activity was measured by Open Field Test while sociability and avoidance were quantified by Mirror Image Stimulation test. Red squirrels co-occurring with the alien species had higher sociability scores and higher between-individual variation in sociability than in red-only sites. Differences in activity and avoidance were not significant. Personality – fitness relationships were not affected by presence or absence of grey squirrels, suggesting that the expression of sociability in red squirrels was not due to short-term selection, but was likely the result of context-related advantages when co-occurring with the competing species.

Estimated Abundance and Distribution of Common Palm Civet (Paradoxurus hermaphroditus, Pallas 1777) in the Rural Landscape of Sukaresmi, West Bandung Regency

Common palm civet (Paradoxurus hermaphroditus, Pallas 1777) is one species of mammal that has high ecological and economical functions. The ecological function of common palm civet is as an agent of forest rejuvenation by dispersing seeds of forest plants. A study to estimate the abundance and distribution of common palm civet was carried out in Sukaresmi village, West Bandung Regency. The study proposed to collect the data of common palm civet abundance and distribution that can be used as a reference for common palm civet protection and conservation measures. Three methods were used: direct survey on common palm civet encounter, direct survey on common palm civet signs, and semi-structured interviews with local informants. The result showed that common palm civet abundance in the study site was estimated between 12 and 66 individuals. The dominant habitat type was kebun campuran (annual-perennial rotation garden) and shrubs. The potential threats to the population of common palm civet was the presence of coucang, bats, squirrels, and frugivorous birds as rivals, dholes as predators, and human as illegal poachers. The effort to protect common palm civet is not yet carried out by the local people as the population is still regarded as abundant and it is not yet of protection concern. Nevertheless, local knowledge about the important roles of common palm civet in the environment can lead to an awareness aimed to reduce illegal poaching.

Nest-Site Selection In A High-Density Colony of Burrowing Owls

Although many Western Burrowing Owl (Athene cunicularia hypugaea) populations have been declining, a high-density population nests at the National Radio Transmission Facility (NRTF), Dixon, California. We compared density at NRTF to densities elsewhere, and nest-site use and reuse to available nest substrates. Breeding pairs numbered 24–44 per year, averaging 34 pairs on 83 ha, the fourth-highest on record. Occupancy of eight artificial nest sites installed in 2000 declined from six pairs in 2006 to one pair in 2007 and 2008, and none afterward. Nearest-neighbor distance among artificial nests averaged half the distance among nest sites in fossorial mammal burrows and concrete half-rounds covering aboveground power cables. Undisturbed clay soils supported pocket gophers (Thomomys bottae) but few ground squirrels (Spermophilus beecheyi), whereas disturbed soils supported both ground squirrels and Burrowing Owls. The presence of both ground squirrels and Burrowing Owls was associated with backfill soils over buried cable, cable covers, and areas where soils bordered impervious surfaces. Nest-site reuse was low, with only 12% of the sites occupied in all study years, 2006–2011. Most (78%) nest sites reused in a subsequent year involved nests in a different burrow or cable cover opening >1 m from the previous year's nest. We recommend research on whether concrete half-rounds might outperform buried utility boxes as artificial nests, especially in conjunction with efforts to conserve the fossorial mammals that naturally excavate burrows used by Burrowing Owls.

A cross-sectional survey to evaluate the pet squirrel population and ownership profiles

While the presence of squirrels in households is growing, little data is published on their status in captivity. A web-based questionnaire for owners was devised eliciting information about them, their squirrels and their squirrels’ husbandry and health. One hundred owners answered the survey, with most respondents being located in Europe (n = 81). Only data from these respondents were analysed. Twenty-five percents of the owners housed an invasive non-native species of European Union concern (S. carolinensis and T. sibiricus), some of which were younger than three years of age and all but one were sexually intact. This is of particular concern, as the acquisition of these invasive species is illegal since 2015 (European Union Regulation 1143/2014), due to the severe threats they pose to biodiversity. Moreover, escapes derived from improper keeping of intact specimens may augment feral populations or establish new colonies. Among 81 cases, only 5% were neutered, mostly for health reasons. Sixty-three percents of the squirrels had health problems, particularly dermatologic (52%) and intestinal disorders (34%). Most owners reported to visit the veterinarian only if their pet was ill rather than for preventive care.This is the first survey on pet squirrel ownership reported to date. Information that emerges from this study will be useful in implementing rational veterinary strategies for managing pet squirrels properly and, in parallel, meeting the challenges arising from private keeping of alien species.

Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds

Providing food for wild birds is perhaps the most widespread intentional interaction between people and wildlife. In the UK, almost half of households feed wild birds, often as peanuts and seed supplied in hanging feeders. Such food is also taken by the introduced, invasive Grey Squirrel Sciurus carolinensis. Little is known of how Grey Squirrels utilise this resource and how they affect feeder use by wild birds. To assess this we recorded the numbers and time spent by animals visiting experimental feeding stations in suburban gardens, and also asked if exclusionary guards (to prevent Grey Squirrel access), food type (peanut, mixed seed), habitat and weather conditions influenced visits. Using automated cameras, we recorded 24,825 bird and 8577 Grey Squirrel visits. On average >44% of the time feeders were utilised, they were being visited by Grey Squirrels. Grey Squirrel presence prevented birds from feeding at the same time (>99.99%). Feeders where Grey Squirrels were dominant were less likely to be visited by birds, even in their absence. Guards reduced Grey Squirrel use to a minimum on seed feeders, and by approximately half on peanut feeders. Squirrels, food type, guard status, habitat and rainfall all influenced bird activity and timing of feeder visits. Our work suggests that Grey Squirrels reduce the availability of supplementary food to wild birds, while gaining large volumes of food resources with corresponding benefits. Given the ubiquity of supplementary feeding, it is likely that this is an important resource for urban Grey Squirrels; feeder guards mitigate this effect.

Public attitudes towards “pest” management: Perceptions on squirrel management strategies in the UK

The impacts of non-native, invasive grey squirrels (Sciurus carolinensis) on broadleaf woodlands and red squirrel population (Sciurus vulgaris) are well recognised among wildlife professionals, yet efforts to control the species across its expanding range require substantial time and resources. Through collaboration, wildlife professionals and communities can more effectively implement the population monitoring and control programmes necessary to conserve native species under threat. However, for such collaboration to be successful, wildlife professionals must first understand public attitudes towards grey squirrels, and the control methods available. Through a national level survey (n = 3758) we examine the UK public's attitudes to red and grey squirrels, and the acceptability of seven control methods. Results show that much of the public have little knowledge of the grey squirrel's negative impacts. In fact, contrary to the notion of a pest species, the presence of grey squirrels is often desirable. Furthermore, those control methods recommended by wildlife professionals are regarded by the public as some of the least acceptable. Those most accepting of controls include males, older generations, those most knowledgeable about squirrels and people who are aware of squirrel management being practiced in their local area. To foster more fruitful collaboration, wildlife professionals should raise awareness of why particular control methods are preferred, highlight the damage grey squirrels cause to other valued species, and offer local communities a variety of roles which contribute to the wider goal of native species conservation.

Reconsidering habitat associations in the Anthropocene

The California ground squirrel (Otospermophilus beecheyi) is generally undervalued despite serving as an ecosystem engineer in grassland ecosystems. Evidence of significant engineering effects by squirrels indicates that population reductions have cascading effects on other species, including several conservation-dependent species. While the theory and practices behind habitat association studies are already well established, our application of this approach helped identify priority management options in degraded grasslands expected to change further under shifts in climate. In this study we conducted surveys for California ground squirrels throughout San Diego County grasslands and examined habitat covariates to determine the ecological variables currently associated with occurrence. The primary objectives were to 1) improve our understanding of the habitat variables associated with squirrel presence, and 2) develop a predictive model for squirrel habitat suitability at a local scale. The most predictive models included significant main effects for percent sand (as a component of soil texture) and vegetation cover. A 10% increase in vegetation cover was associated with 1.3 fold lower odds of squirrel presence, whereas a 10% increase in percent sand was associated with 2.0 times higher odds of squirrel presence. Comparison of the predictive accuracy of soil texture data at two scales (fine-scale field vs. landscape scale GIS layers) showed fine-scale field sampling has greater predictive strength. Because soil type is a logistically non-malleable factor for wildlife managers, it is important to categorize management sites by soil type to identify the potential for promoting fossorial species on the landscape. With the prospect of shifting landscape ecotones due to climate change, it is as important to understand the basic habitat requirements of keystone species as for rare species.

Assessment of Detection Methods and Vegetation Associations for Introduced Finlayson's Squirrels (Callosciurus finlaysonii) in Italy.

Managing biological invasions requires rapid, cost-effective assessments of introduced species' occurrence, and a good understanding of the species' vegetation associations. This is particularly true for species that are elusive or may spread rapidly. Finlayson's squirrel (Callosciurus finlaysonii) is native to Thailand and southeastern Asia, and two introduced populations occur in peninsular Italy. One of the two introduced populations is rapidly expanding, but neither effective monitoring protocols nor reliable information on vegetation associations are available. To fill this gap, we conducted visual surveys and hair tube sampling in a periurban landscape of southern Italy to compare the effectiveness of these two methods in assessing presence of Finlayson's squirrel. We also determined the species' association with vegetation types at detection locations and nesting sites. Both visual and hair tube sampling effectively assessed the species' presence, but hair tubes resulted in fewer false absences. Moreover, when we controlled for the costs of labor and equipment, hair tubes were 33.1% less expensive than visual sampling. Presence of squirrels and their nests was positively correlated with shrub species richness, indicating that the occurrence of forests with well-developed understory may inhibit the spread of the species.

Biodiversity threats from outside to inside: effects of alien grey squirrel (Sciurus carolinensis) on helminth community of native red squirrel (Sciurus vulgaris)

Biological invasions are among the major causes of biodiversity loss worldwide, and parasites carried or acquired by invaders may represent an added threat to native species. We compared gastrointestinal helminth communities of native Eurasian red squirrels (Sciurus vulgaris) in the presence and absence of introduced Eastern grey squirrels (Sciurus carolinensis) to detect alterations induced by the alien species. In particular, we investigated whether spillover of a North American nematode Strongyloides robustus occurs and whether prevalence of a local parasite Trypanoxyuris sciuri in red squirrels is affected by grey squirrel presence. The probability of being infected by both parasites was significantly higher in areas co-inhabited by the alien species, where 61% of examined red squirrels (n = 49) were infected by S. robustus and 90% by T. sciuri. Conversely, in red-only areas, the two parasites infected only 5 and 70% of individuals (n = 60). Overall, our findings support the hypothesis that red squirrels acquire S. robustus via spillover from the alien congener and suggest that invaders' presence may also indirectly affect infection by local parasites through mechanisms diverse than spill-back and linked to the increased competitive pressure to which red squirrels are subjected. These results indicate that the impact of grey squirrel on red squirrels may have been underestimated and highlight the importance of investigating variation in macroparasite communities of native species threatened by alien competitors.

The changing patterns in the distribution of red and grey squirrels in the North of England and Scotland between 1991 and 2010 based on volunteer surveys

In the UK, alien grey squirrels have been replacing the native red squirrel for >100 years and by the turn of the century the distribution of grey squirrels had extended to most of central and southern England and Wales (apart from some islands), and large parts of Scotland and Ireland. To understand how this species replacement may continue into the future, we explore 20 years of squirrel records (1991-2010) collected in an unsystematic way by volunteers in northern England and Scotland. To aid analysis, we standardised the data to one record of squirrel presence per 4 km square per year in each of six geographic regions, two in northern England and four in Scotland. Over the 20 years and across all regions, the number of 4 km squares that returned the presence of squirrels increased from 23% to 80%. The evolving distribution pattern of red and grey squirrels differed among the regions and was complex with occupancy records for many 4 km squares changing from red to grey squirrel from one year to the next, but also some changing from grey to red squirrel. The net rate of change, however, was from red to grey squirrel with the exception of the more recent years, 2007-2010, when this trend became less distinct. Estimates of the complete loss of red squirrels assuming current trends, varied from the 2020s in northern England to 2104 in North East Scotland. The recent incertitudes in the replacement of red by grey squirrels may, at least in part, result from increasing efforts to control grey squirrels in these regions. Although the volunteer data presented are valuable, monitoring aims must be clearly defined and sampling designs involving volunteers and professionals must be systematic and of sufficient effort to obtain reliable information on changes in distribution and population trends. Download the complete issue.