Effects of forest structure on the distribution of southern flying squirrels (Glaucomys volans) in urban parks

Although southern flying squirrels (Glaucomys volans) are present in many urban parks, squirrel-habitat relationships in such areas are poorly understood, limiting conservation efforts. Our objective was to quantify the effects of forest structure at multiple scales on flying squirrel distribution in New York City (NYC) parks. From 18 June–24 August 2001, we captured flying squirrels in 5 New York City parks and measured forest structure at the ground, shrub, understory, and overstory levels at trap sites. To examine the importance of forest structure to squirrels, we compared (1) habitat variables between trap stations where squirrels were captured and not captured and (2) habitat variables between parks with and without documented squirrel populations. Our data suggest that areas with forests containing smaller trees at higher densities, dense woody ground cover, and little herbaceous ground vegetation may not provide the food, cavities, ease of movement, or allow predator detection necessary to be used by or support flying squirrel populations. Other factors, such as the size and density of stumps and snags may be important to non-urban squirrel populations, but not populations in NYC parks. Because NYC parks contain almost all of the remaining woodlands within the City, forests within these areas should be a conservation priority.     

Seasonal activity patterns of sympatric eastern gray squirrels (Sciurus carolinensis) and fox squirrels (Sciurus niger) in a Midwestern metropolitan region

Niche partitioning reduces interspecific competition, facilitating coexistence. In urban ecosystems, however, habitat loss reduces species’ ability to spatially partition activity. Temporal partitioning may thus increase in urban areas as species, unable to avoid each other spatially, partition time to avoid competition. In Midwestern US cities, eastern gray squirrels (Sciurus carolinensis) and fox squirrels (S. niger) co-occur and compete for resources. We identified urban gray and fox squirrel activity patterns and how they vary with season, land cover, and among sites where they do and do not co-occur using camera-trap data. Both species’ activity patterns varied with season and canopy and impervious surface cover. Gray squirrel activity patterns varied in the presence of fox squirrels only in the fall, providing limited support for our temporal partitioning hypothesis. Temporal niche partitioning may thus play a role in supporting these species co-existence when competition is seasonally-elevated (e.g., fall hording), but appears less important in other seasons.

     

Reproduction, juvenile survival and retention in an urban fox squirrel population

Fox squirrels in an urban environment had an average litter size of 2.83 (95% CI 2.5, 3.16) which was similar to rural populations. Nonetheless, the proportion of squirrels reproductively active during the summer/fall breeding season (0.73) and annually (spring + summer/fall) was higher (1.23) than previously recorded for non-manipulated rural populations. The average monthly survival rate () of urban juvenile fox squirrels during the first 14 weeks of life was higher than reported for adult populations in the area. High rates of reproduction and juvenile survival yielded high juvenile to adult ratios (juveniles/adults) averaging 0.44. Retention of juveniles after 6 months (15%) was significantly less (χ ² = 7.24, p = 0.0071) than adults/subadults (40%). Results suggest that the urban environment provides quality habitat for fox squirrels and fox squirrels in urban environments have the potential to be a source population for surrounding suburban and rural environments.     

Gray squirrel density,habitat suitability,and behavior in urban parks

Increased density, increased intraspecific aggression, and a reduced fear of humans have been suggested as the more observable and frequently described characteristics of wildlife species undergoing synurbization, the process of becoming urbanized. The relationship among these variables and how they may be related to environmental variables that change with urbanization is poorly understood. In this paper we explore the relationship between density, intraspecific aggression, and reduced fear of humans in urban populations of gray squirrel. In the summer and fall of 2003 and 2004, we studied a park with a documented high density of gray squirrels, Lafayette Park, Washington, DC, and six urban parks in Baltimore, MD with unknown squirrel densities. We used linear regression (SAS Institute, SAS/STAT user’s guide. SAS Institute, Cary, NC, 2005) to determine if there was a relationship (P < 0.05) between squirrel density and intraspecific aggression, squirrel density and reduced fear of humans (wariness), and squirrel density and habitat suitability. We found a positive association between density and intraspecific aggression (R ² = 0.81, P < 0.00). A negative relationship between density and wariness (, P < 0.00). However, no relationship was evident between habitat suitability and squirrel density (, P = 0.437).     

Seasonal comparisons of daily activity budgets of gray squirrels (Sciurus carolinensis) in urban areas

Gray squirrels (Sciurus carolinensis) use trees for various resource needs in urban and nonurban settings; particularly, mast producing trees which are the preferred and supplemental foods for the species. During periods of abundant mast availability, less time will be invested in foraging because of the higher success rate stemming from the increased ability to locate food items. Conversely, in periods of reduced mast availability, more time will be invested in foraging. However, correlations between food availability and foraging effort are only supported under the assumption that gray squirrels rely significantly on mast as a preferred or supplemental food source (Nixon et al, J Wildl Manag 39:1–25, 1975). Therefore, given the seasonal variation in the availability of mast, there should also be correlating seasonal variations in foraging effort. In this paper, we will examine daily and seasonal time-activity budgets of gray squirrels in urban areas. We studied the time-activity budgets of gray squirrels in six urban parks in Baltimore, MD. Seasonal frequencies of activities were expressed as percent occurrence and seasonal differences in activities were analyzed using a Tukey Studentized multiple range test for significance. We found that the activity with highest percent occurrence was forage (2003, summer: 23.8 %, fall: 25.9 %; 2004, summer: 23.1 %, fall: 25.2 %), followed by feed and store, all activities associated with food. Results of the Tukey Studentized multiple range test for seasonal differences of activities yielded significant results (P?P?=?0.003); fall 2003 and fall 2004 (P?=?0.048).     

Squirrels in suburbia: influence of urbanisation on the occurrence and distribution of a common exotic mammal

Urbanisation is widely considered to promote the establishment of non-native species, but there is limited empirical evidence of the ecological factors driving their responses. The grey squirrel Sciurus carolinensis (Gmelin 1788) is native to North America, but is widespread in the UK and is starting to spread across Europe. It is regarded as one of the world’s worst invasive animals due to its adverse impacts on native biodiversity. We use the non-native grey squirrel population in Sheffield (UK) as a case study to assess which factors limit its distribution and abundance in urban environments. In 2010 the city-wide population of adult squirrels peaked at an estimated 6539 in autumn (0.46 squirrels/ha), with maximum local densities of 8.29/ha. These densities appear to be slightly lower than those recorded in urban environments in the species’ native range. Grey squirrels occurred more frequently at urban sites with larger amounts of green-space in the surrounding region. Local habitat characteristics were, however, more powerful predictors of urban grey squirrel occurrence and abundance than regional availability of green space. Canopy cover, seed bearing trees and supplementary feeders, provided for garden birds, positively influenced grey squirrels. The potential for grey squirrels to connect city dwellers with nature thus appears to be highest in urban locations that have considerable capacity to support native biodiversity. The beneficial impacts of supplementary feeding on grey squirrel populations is notable given concerns that squirrels can adversely influence bird populations. These habitat associations also imply that grey squirrels typically respond negatively to urbanisation, which challenges arguments that urbanisation favours exotic species.     

Urban open spaces from a dispersal perspective: lessons from an individual-based model approach to assess the effects of landscape patterns on the viability of wildlife populations

Green areas drawn on a city plan represent open spaces that have different meanings for humans and wildlife. Diverse kinds of green may influence species viability in urban environments. It is necessary to understand what those areas mean for wildlife populations and how land-use changes affect habitats and movements for making scientifically defensible planning and design decisions. My objective was to demonstrate how open space and urban development patterns affect the viability of wildlife populations in urbanizing landscapes from a movements perspective. Eight scenarios for 2060 for an urbanizing area near Portland, Oregon combined four open space (none, corridors, parks, and network) with two urban development patterns (compact and dispersed). Dispersal model HexSim simulated three target species – Red-legged frog (Rana aurora aurora), Western meadowlark (Sturnella neclecta) and Douglas squirrel (Tamasciurus douglasii) – movements on those scenarios to compare and contrast sustained populations to the ca. 2010 baseline landscape. Network scenarios presented the largest number of frog breeders. Greenway scenarios showed the largest populations of squirrels. Park and network scenarios sustained viable populations of meadowlarks, but park scenarios performed best. Compact development scenarios performed best for most indicators, while dispersed development scenarios performed better for meadowlarks. Network scenarios performed best when considering the collective of species. Networks presented more diverse habitats, sustaining higher diversity of species. For plans to sustain more species, more comprehensive and diverse habitats must be promoted, otherwise trade-offs should be expected – like the extinction of meadowlarks in greenway scenarios.

     

Traffic related mortality in a red squirrel (Sciurus vulgaris) population receiving supplemental feeding

This paper presents data on red squirrel road casualties recorded in the four-year period 1993–1996 within the National Trust reserve and adjacent suburban gardens of Formby, Lancashire, England. A total of 130 adults and six subadults were recorded as road traffic victims. Road casualties accounted for 65% of the recorded adult mortality (26.7% of the reserve total and 88% in the suburban habitat). Adult males were killed more frequently than females during the winter months. Road traffic deaths were highly seasonal with a clear peak in the autumn months (53.7% of all casualties). It is suggested that this may be related to seasonal variation in foraging behavior and to the abundance of natural and supplemental foods.     

Coming in like a wrecking-ball: are native Eurasian red squirrels displacing invasive Siberian chipmunks? A study from an urban park

Alien squirrels may seriously threaten native species by means of interspecific competition. In our work, we analysed whether the distribution of alien Siberian chipmunks within the Sigurtà Garden urban park (north-eastern Italy) changed after the natural spread of native Eurasian red squirrels in a 20-year period. Distribution of both squirrels was estimated through a citizen-science approach, in the first 10-year after red squirrel arrival 1 (i.e. Decade 1: 1997–2006) and in the second 10-year interval (i.e. Decade 2: 2007–2017). We compared habitat use of both species and we assessed whether a vertical segregation occurred through a dissimilarity index. Woodlands were selected by both species in both decades. Red squirrels also selected tree lines in Decade 1. A vertical segregation was apparent in Decade 1, whereas in Decade 2 both squirrel species were observed on the lowest branches or on the ground, where they are fed by humans. This was also confirmed by the habitat niche-overlap index, which increased in Decade 2. The extent of occurrence of Sciurus vulgaris increased throughout the park, whereas those of Eutamias sibiricus decreased. Differently from what is usually observed with alien squirrels, the spread of the native species appears to be halting and reversing the expansion of the non-native one.     

Urban parakeets in Northern Illinois: A 40-year perspective

Monk parakeets (Myiopsitta monachus) are the most abundant and widely distributed of the naturalized parrots in the United States. We summarize monk parakeet population data from 1970 to 2010 for northern Illinois, one of the best-known populations. Throughout the 1970s, parakeets were seen in small numbers at scattered locations, but none of the nesting sites persisted and the birds either died or moved elsewhere. The species became established in the Hyde Park neighborhood of Chicago in 1979 and this population grew exponentially and expanded over the next 25?years, doubling in size every 2 to 3?years. In the mid to late 1990s parakeets became established in many other localities in the Chicago region. The population in Hyde Park began to rapidly decline in 2005, a trend also exhibited in national counts. The reasons for this decline are unknown but we suggest that the decline is more apparent than real and that the decline in Hyde Park is the result of shifts in population structure from a few dense aggregations to progressively more spatially separated smaller groups. As evidence for this, the population of parakeets in the greater Chicago region does not appear to have declined but is still growing in size and distribution. Monk parakeets are a novel addition to many urban ecosystems, with a neutral impact to most other bird species but an increasingly complex interaction with human residents in urban areas.     

Coyote,fox, and bobcat response to anthropogenic and natural landscape features in a small urban area

Increasing urbanization across the southeastern United States presents unique challenges for wildlife; however certain species have learned to adapt and thrive in these environments. Coyotes (Canis latrans), bobcats (Lynx rufus), red foxes (Vulpes vulpes) and gray foxes (Urocyon cinereoargenteus) are four common medium-sized carnivores that have become closely associated with urban areas. The goal for this study was to determine how urban landscape features influence density and occurrence of these species in a small urban area and to evaluate if any effects were similar to those observed in larger urban areas. We conducted two eight-week camera surveys in the city of Nacogdoches, Texas (pop. 32,699) and immediate surrounding areas in summer and fall 2013. We evaluated single-season spatially explicit capture-recapture and occupancy models to estimate density, and occurrence, respectively, based on anthropogenic and natural features around each camera site. Coyotes (fall: 1.38 coyotes/km²) and bobcats (fall: 0.64 coyotes/km²) were associated with areas of green space, but their response to large and small green spaces changed seasonally. Conversely, red foxes (fall: 2.53 red foxes/km²) were more likely to occur near developed areas and were less detectable in areas with greater probability of coyote presence in fall only. In summer, gray foxes (fall: 0.05 gray foxes/km²) were more likely to occur in areas with lower building density and closer to buildings. This study indicates coyotes, foxes and bobcats respond to small-scale urbanization in a similar manner as large-scale urbanization.     

Inequalities,Democracy, and Fieldwork in the Chicago Schools of Yesterday and Today

Barriers to public discourse and participation in a democracy were central to the social reform concerns of Mead. Urban ethnographies of the last thirty years that are associated with the University of Chicago and the Chicago School contribute to this aspect of Mead's work. These ethnographies help to illuminate how extreme poverty and racism affect public discourse between groups. The Chicago tradition linked to the work of Park and Wirth has emphasized the importance of persistent inequalities and a lack of public discourse and participation rather than a symbolic interactionist approach that emphasizes the ability of people to create a place for themselves in an open, fluid world. Through field research in poor, often minority urban communities, the sociologists linked more closely to the former group have explored issues of the maintenance of patterns of extreme inequalities, the muting of public dialogue, and blockages to participation while maintaining a focus on the agency of the poor and their efforts to create their social worlds.     

Increased differentiation between individuals,but no genetic isolation from adjacent rural individuals in an urban red squirrel population

Whether or not individuals in cities and adjacent rural areas form separate populations depends on the origin of urbanized individuals. The rural individuals may have simply gradually invaded the city. Alternatively, the urbanization depended on arrival of individuals with specific adaptations for city life. A population within the city could also remain separated from adjacent rural populations if there are physical or behavioural dispersal barriers lowering the possibility of genetic exchange between individuals. All this is linked to dispersal behaviour of the species as gene flow is determined by distances moved during dispersal. In this study, we used microsatellite markers to evaluate whether or not Eurasian red squirrel (Sciurus vulgaris) individuals in an urban environment are genetically separated from their sub-urban/rural counterparts. Using radio-telemetry, we also studied natal dispersal distances of urban red squirrels to evaluate the potential for gene flow within the city. We observed no indication that urban squirrels had been genetically isolated from rural squirrels. In addition, increased amount of built area did not explain differentiation between urban individuals, further indicating that there were no barriers restricting movement. Still, the genetic differentiation within the city was increased and natal dispersal distances relatively short, perhaps indicating lack of need to move long distances in the urban environment. We conclude that urban and adjacent rural squirrels were part of the same larger population with gene flow in and out from the city. Yet, urbanization was related to increased genetic differentiation, indicating different spatial genetic structure in urban and rural populations.     

Bird diversity in a subtropical South-American City: effects of noise levels,arborisation and human population density

Cities are highly modified environments in which the only areas that resemble natural landscapes are urban parks with low human population density. Attempts are frequently made to maintain high bird diversity in cities for aesthetic or educational reasons. However, it remains unclear whether local site characteristics are important in determining bird assemblage composition or whether simplification of the assemblage is an inevitable consequence of the changes associated with human population density. From May 1998 to December 1999, we undertook bird counts at 521 points in Porto Alegre, Rio Grande do Sul, southern Brazil. Our main goal was to understand the pattern of distribution of the bird species richness and density within the city and determine which variables most affect species assemblages. We recorded 132 species belonging to 43 families that are common in Rio Grande do Sul and obtained quantitative data on 121 species in survey sites. The two most abundant species (House Sparrow, Passer domesticus and Rock dove, Columba livia) were exotics. Analysis based on a reduced subset of 134 points surveyed in spring/early summer suggested that there was a North–south gradient in assemblage structure. Variation in assemblage structure was also affected by the number of trees, urban noise and human population density. However, human population density had a much smaller effect on richness and assemblage structure than variables subject to management, such as tree density and noise levels. These results suggest that complex communities may be maintained in densely populated urban areas of sub-tropical South-America given adequate urban planning.     

The influence of anthropogenic resources on multi-scale habitat selection by raccoons

With the continuing spread of urban areas, gaining a greater understanding of the effect of human presence on wildlife species is essential for wildlife managers. We determined the influence of anthropogenic resources on home range size and habitat selection of raccoons (Procyon lotor) during summer (June–August) 1996–2000 for 120 raccoons at three sites exposed to varying levels of urbanization and anthropogenic resources, specifically food. Home range estimates were larger (P < 0.05) at the rural site than the suburban and urban sites for both genders. We used compositional analysis to examine raccoon habitat selection at the second-order home range, second-order core area, and third-order home range scales. Woodland was consistently a highly-selected habitat type for both sexes at every spatial scale. Relative to other habitat types, habitat associated with human-related food (human use areas) was selected most often at the urban site, intermediately at the suburban site, and not selected at the rural site. Spatial scale also affected habitat selection. Human use areas were preferentially selected at the second- and third-order level at the urban site, third-order level only at the suburban site, and at neither level at the rural site. Additionally, intersexual differences in habitat selection were reduced at the urban site, with both sexes preferentially selecting for human use areas as well as woodland habitat. Smaller home ranges in urbanized environments are often attributed to the abundant and concentrated anthropogenic resources associated with human activity, but with little empirical support. Our habitat selection analyses followed our predictions that raccoon foraging is strongly influenced by the artificial distribution and abundance of human-related food. Male and female raccoons in urban areas reduce their foraging patterns and focus their foraging activity on anthropogenic foods.     

Urban predator–prey association: coyote and deer distributions in the Chicago metropolitan area

We examined how predator or prey presence, as well as local and landscape factors, influence the distribution of coyotes (Canis latrans) and white-tailed deer (Odocoileus virginianus) in the Chicago metropolitan area. We collected data for 2 years at 93 study sites along 3 transects of urbanization using motion-triggered cameras. Our primary objective was to determine the relationship among coyote and deer spatial and temporal distribution, habitat characteristics, and human activity using multi-season patch occupancy models. Coyote occupancy was most strongly linked to rates of site visitation by humans and dogs, and was more likely farther from the urban center, with coyote colonization of sites inversely related to road density, housing density, and human and dog site visitation. Deer more frequently occupied sites with high canopy cover near water sources and colonized smaller sites with reduced housing density and human and dog presence. Expected predator–prey dynamics were altered in this highly urban system. Though we predicted deer would avoid coyotes on the landscape based on an “ecology of fear” framework, deer and coyote occupancy showed a strong positive association. We suggest that a scarcity of quality habitat in urban areas may cause the species to co-occupy habitat despite potential fawn predation. Modifying human foot traffic in green spaces may represent a useful tool for management and conservation of large urban mammals.     

Charles S. Johnson’s the Negro in Chicago

Charles S. Johnson’s classic study of the Chicago race riot of 1919,The Negro in Chicago, can provide contemporary social scientists with valuable historical insight into urban race relations and a model of methodological comprehensiveness. This review of Johnson’s study suggests the influence of the Chicago School of Sociology and especially of Robert Park on its methodological and conceptual framework. In contrast to the tendency of many recent studies of black urban communities to maintain a narrow theoretical and empirical focus,The Negro in Chicago draws on a wide array of types of data and uses an organic metaphor to suggest the complex interrelatedness of urban residents in the many contexts of their daily lives.     

Non-native plants in the understory of riparian forests across a land use gradient in the Southeast

As urbanization expands into rural areas, an increase in the number of non-native plant species at the urban-rural interface is expected due in large part to the increased availability of propagules from ornamental plantings. A study investigating the distribution of non-native plants in the understories of riparian forests across an urban-to-rural gradient north of Columbus, GA was initiated in 2003. A significantly greater number of non-native plant species occurred at the urban sites and at one site at the urban-rural interface, where 20 to 33% of the species encountered were non-native. In contrast, at the more rural sites non-native species comprised 4–14% of the total number of species. However, the importance values of non-native species as a whole did not change significantly across the land use gradient due to the high frequency and abundance of three non-native species (Ligustrum sinense, Lonicera japonica, and Microstegium vimineum) in the majority of the watersheds. Reductions in species richness and overstory reproduction associated with these non-natives could impact long-term forest structure and ecosystem function.     

Survey of feral rock doves (Columba livia) in Amsterdam, a bird-human association

We carried out a survey of the feral rock doves (Columba livia) visible in the public areas of the fourteen Town Councils in Amsterdam. The objectives were to detect the preferential locations of the feral pigeons and to obtain reference values of their population sizes in order to be able to evaluate the effect of possible control measures. We registered 354 locations were twenty or more feral pigeons were visible during feeding. In these locations, averaged over ten to twelve counts, we counted 10,056 pigeons. Moreover we observed that at another 541 locations at least once five pigeons were visible during feeding. In all 894 locations we counted, averaged over four counts, 11,885 pigeons. By Town Council, we calculated strong positive correlations between the average number of pigeons per hectare, the human population density, the number of houses and the yearly number of kilos organic waste per hectare.