Sound attenuation properties of the habitats occupied by two species of tree squirrels affect whether or not the squirrels will make alarm calls. Sound properties have been compared among habitats, microhabitats, weather conditions and seasons. In each case alarm calling activity is consistent with the hypothesis that calling behavior is acted upon by natural selection: calling occurs when squirrel calls carry well, and thus where the potential for communication is high.

Tree squirrels play an important role in the maintenance of forest ecosystems by functioning as seed and fungal spore dispersers, forest regenerators, and prey for forest predators. The highest species richness for tree squirrels occurs in tropical forests and these species are also the least studied. We conducted distance sampling to estimate population density, measured habitat variables to investigate forest characteristics that influence habitat selection and feeding site selection at three different scales, and conducted observations to obtain knowledge about activity pattern and behavior of Neotropical pygmy squirrels and Amazon red squirrels in the Peruvian Amazon. Density of Neotropical pygmy squirrels was 0.10 and 0.14 individuals/ha for 2009 and 2010. Activity peaked in early morning, squirrels were found mainly in the canopy but never on the ground, and frequency of behaviors differed by time and story level. Neotropical pygmy squirrels used mainly high and low restinga and areas that had more large trees. Squirrels also used species of trees disproportionately to availability. Neotropical pygmy squirrels seem to be associated with features related to mature forests. Amazon red squirrels use mainly high and low restinga and selected Astrocaryum and Attalea palm trees that were taller and larger as foraging sites compared to random locations. Amazon red squirrels used all vertical strata of the forest and the main behaviors observed were travel and forage. Behaviors were similar among time periods but differed in frequency by vertical strata. Although Amazon red squirrels used vegetation communities differently than their availability and selected for tree characteristics, they did not select for site characteristics and this is different from other tree squirrel species. We also conducted surveys during a wet and a dry year to investigate and estimate diversity of diurnal mammals. We assessed the vertical strata of the forest to determine if diversity index varied by story level, and estimated alpha, beta, and gamma diversity. Overall mammal diversity did not differ between wet and dry years. Diversity index differed by story level between years, but was the highest in the canopy for both years. Alpha diversity was higher in the dry year, and gamma and beta diversity were higher in the wet year. Frequency of sightings of species was influenced by time of day and varied by story level. Protection of continuous, mature forests with large canopies has important conservation implications as these areas most likely protect the greatest diversity of mammals while also providing shelter and food for other taxa.

This thesis examines how Eastern grey squirrels, Sciurus carolinensis, modify their foraging and hoarding behaviour in relation to different risks, particularly those which involve a trade-off between securing food resources and avoiding a negative outcome with a competitor. While foraging for food to eat and hoard, squirrels must compete with conspecifics and heterospecifics for access to resources, and they must ensure the safety of their food hoards from onlookers or opportunistic pilferers. While engaging in these behaviours in the most efficient way, they must also avoid being predated upon. Five studies were conducted to further understanding of grey squirrel foraging, hoarding and pilferage behaviours, and how they are affected by different risk factors. The data in this thesis provide experimental evidence that grey squirrels respond directly to conspecific presence as a cue of pilferage risk and adjust their behaviour in ways that may help to reduce cache theft. The data also support the view that conspecific and heterospecific competitors pose risks to foraging and caching, with squirrels modifying their behaviour in ways that serve to avoid negative competitive interactions. Predation risk was found to be particularly disruptive to foraging behaviour, and it also had a seasonal effect upon pilferage rates of experimenter-made caches. A variety of strategies that squirrels might use to pilfer caches were investigated, however, the data did not provide a clear indication of pilferage strategy used by squirrels; they did not seem to use observational spatial memory, and they did not simply pilfer in profitable foraging locations. This thesis raises questions about the mechanisms grey squirrels use to assess pilferage risk and how they engage in pilferage in comparison to other caching species; the studies conducted illustrate different methods that future research could use to investigate food hoarding and pilfering behaviour in wild and captive squirrels.

Successful management of an invasive species requires in depth knowledge of the invader, the invaded ecosystem, and their interactions. The complexity of the species-system interactions can be reduced and represented in ecological models for better comprehension. In this study, a spatially explicit population model was created using the RAMAS software package to simulate the past and future invasion dynamics of the eastern grey squirrel (Sciurus carolinensis) in the fragmented habitat in case study areas in Ireland. This invasive squirrel species causes economic damage by bark stripping forest crops and is associated with the decline of its native congener (S. vulgaris). Three combinations of demographic and dispersal parameters, which best matched the distribution of the species shortly after introduction, were used to simulate invasion dynamics. Future population expansion was modeled under scenarios of no control and two different management strategies: fatal culls and immunocontraceptive vaccination programmes. In the absence of control, the grey squirrel range is predicted to expand to the south and southwest of Ireland endangering internationally important habitats, vulnerable forest crops, and the native red squirrel. The model revealed that region-wide intensive and coordinated culls would have the greatest impact on grey squirrel populations. Control strategies consisting solely of immunocontraceptive vaccines, often preferred by public interest groups, are predicted to be less effective. Complete eradication of the grey squirrel from Ireland is not economically feasible and strategic evidence-based management is required to limit further range expansion. Ecological models can be used to choose between informed management strategies based on predicted outcomes.

The grey squirrel (Sciurus carolinensis) has wildtype and melanic (dark) colour morphs. Melanism is associated with variations in the melanocortin-1 receptor (MC1R) gene in a number of species. The MC1R protein is a G-protein coupled receptor, predominantly expressed in melanocytes, where it is a key regulator of pigment production. To investigate the genetic and molecular basis of melanism, the MC1R genes of the wildtype and melanic grey squirrel were sequenced. The wildtype (MC1R-wt) and melanic (MC1RΔ24) variants of the MC1R were then functionally characterised in a cell-based assay. The MC1R gene of the grey squirrel was found to have a 24 base pair (bp) deletion associated with melanism. The MC1R is typically activated by its agonist, the alpha-melanocyte stimulating hormone (α-MSH), which stimulates dark pigment production by raising intracellular cAMP levels. Conversely, the MC1R is inactivated by its inverse agonist, the agouti signalling protein (ASIP), which stops dark pigment production by lowering intracellular cAMP levels. To investigate the effects that the 24 bp deletion have on receptor function, MC1R-wt and MC1RΔ24 genes were transfected into HEK293 cells. Cells expressing either MC1R-wt or MC1RΔ24 were stimulated with α-MSH or ASIP and intracellular cAMP levels were measured. Unstimulated MC1RΔ24 cells showed higher basal activity than the MC1R-wt cells. Both MC1R-wt and MC1RΔ24 cells responded to α-MSH with a concentration-dependent increase in intracellular cAMP. However, while the MC1Rwt cells responded to ASIP with a concentration-dependent decrease in intracellular cAMP, MC1RΔ24 cells responded with an increase in cAMP. Melanism in the grey squirrel is associated with a 24 bp deletion in the MC1R. Cells expressing MC1RΔ24 have higher basal levels of cAMP than MC1R-wt cells. ASIP acts as an inverse agonist to the MC1R-wt but as an agonist to the MC1RΔ24. As MC1RΔ24 cells have higher levels of cAMP, and higher levels of cAMP lead to dark pigment production, the 24 bp deletion is the likely molecular cause of melanism in the grey squirrel.

After decades of suppression, fire is returning to forests of western United States. Understanding responses of wildlife species to fire is essential to native species conservation because contemporary fires may not have the same effects on forest structure and landscape patterns as historical fires. I used radio-telemetry to investigate effects of fire severity and heterogeneity on habitat selection of Mexican fox squirrels, Sciurus nayaritensis chiricahuae. Vegetation within home ranges was characterized by more open understory and larger trees than random locations. Squirrels used areas burned at low severity more than unburned areas and those burned at higher severities. Squirrels used areas of moderate burn heterogeneity more than areas of low or high heterogeneity. Return of low-severity fire can help restore habitat for Mexican fox squirrels and other native species in forests with a historical regime of low-severity fire and contribute to understanding of the role of fire in forest ecosystems.

Made available in DSpace on 2014-06-12T15:03:51Z (GMT). No. of bitstreams: 2 arquivo4677_1.pdf: 3456179 bytes, checksum: a2042c249159fcea2222303c58cb018a (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2004 / As interações planta dispersor modulam o valor adaptativo das espécies de plantas e animais, atuando diretamente nas características reprodutivas das espécies vegetais e na história de vida dos animais. O padrão de frugivoria influencia no padrão da chuva de sementes de plantas, nas taxas de predação por invertebrados e, conseqüentemente, na germinação, sobrevivência de plântulas e no recrutamento de adultos. Considerando que as características demográficas de uma espécie são resultantes do recrutamento de indivíduos adultos, o padrão de forrageamento de animais dispersores é parcialmente responsável pela manutenção da organização de comunidades. No que se refere à dispersão mediada por roedores scatterhoarders, é sugerido um padrão de adaptação ao sistema planta dispersor em que as plantas envolvidas investiriam na produção de sementes grandes e comestíveis e com grande produção e maturação sincronizada, para que a oferta de recurso seja atraente para os predadores. E, em contrapartida, estes roedores realizariam armazenamento (por enterramento), para evitar competição, e propiciariam uma maior realocação de sementes, as quais seriam enterradas em baixas densidades e distantes da fonte do recurso, o que as protegeria do ataque de outros predadores. O enfoque desta pesquisa foi reconhecer padrões no comportamento do roedor scatterhoarder, Sciurus aestuans, com o objetivo de estabelecer parâmetros relacionados à atividade de frugivoria e de avaliar seus efeitos nas características populacionais de espécies arbóreas. Esta pesquisa foi realizada em fragmentos de floresta ombrófila densa montana no município de Santa Teresa (ES). Os fragmentos estudados apresentam influências de processos causadores de defaunação. As espécies envolvidas nos experimentos podem ser incluídas, a partir das características morfológicas dos seus frutos, na síndrome específica associada à dispersão por roedores. As espécies estudadas foram: (1) Attalea oleifera, Syagrus pseudococos, S. ruschiana, Polyandrococos caudescens, Bactris setosa e Euterpe edulis da família Arecaceae; (2) Licania kunthiana e L. leptostachia da família Chrysobalanaceae; (3) Caryocar edule da família Cariocaraceae; (4) Hymenea aurea da família Caesalpinaceae; e (5) Vantanea obovata da família Humiriaceae. Os resultados indicam uma seletividade de S. aestuans, quando comparadas diferentes espécies com a mesma síndrome associada a roedores. O esquilo prefere espécies de plantas com alta produção, grandes frutos com poucas sementes envolvidas por endocarpos resistentes e que não são usadas por outros predadores de sementes arborícolas. E, dentro desta síndrome, foi observada uma maior permanência de S. aestuans e um padrão de manipulação dos frutos mais elaborado em espécies com maior produtividade e com frutos de maior tamanho e dureza. Além disso, houve uma comprovação direta de menores taxas de predação e maiores taxas de armazenamento para espécies com frutos maiores. São poucos os trabalhos relacionados ao padrão de forrageamento de predadores de sementes da floresta Atlântica e as suas influências nas características reprodutivas das plantas associadas. Este trabalho tem como principal mérito apresentar padrões de comportamento até então não quantificados ou presenciados e fornecer subsídios para investigações mais profundas no que se refere às interações mutualísticas envolvendo esta espécie de esquilo em floresta Atlântica

The southern fox squirrel (Sciurus niger niger) has the northernmost part of its range in Virginia. For the past 100 years, southern fox squirrels have been declining due to habitat fragmentation, cover type conversion, and fire suppression. Decrease in growing season burns, hardwood encroachment and forest mesophication have transformed pine hardwood woodlands and pine (Pinus spp.) savanna habitats that southern fox squirrels prefer to hardwood dominant habitats that eastern gray squirrels (Sciurus carolinenisis) prefer. These habitat changes have the potential to increase competition among the two species. The main objectives of my study were to investigate the general resource needs, occupancy, and home range of southern fox squirrels as well as the impact of resource partitioning and possible competition with eastern gray squirrels in the Piedmont and Coastal Plain of Virginia. I captured, radio collared and tracked four individuals at Big Woods Wildlife Management area and Piney Grove Complex using 95% and 50% kernel density estimate. I found an average male home range 173.49 ha (SE = 25.73, N = 2) and 40.62 ha (SE = 5.87, N = 2) and an average female home range of 28.51 ha (SE = 0.49, N = 2) and 4.71 ha (SE = 0.34, N = 2). I then identified the second and third order habitat selection in which my top models identified selection for pine savanna cover types (β = 2.095, SE = 0.158), increasing number of burns since 2019 (β =1.24, SE = 0.098), and decreased time between burns (β = -0.233, SE = 0.097). I used two-species occupancy modeling which reflected that gray squirrel occupancy increased with increasing time since last prescribed burn. However, southern fox squirrel occupancy, in the absence of gray squirrels, decreased with increasing time since last burn. My informed single-season occupancy model confirmed that southern fox squirrel occupancy decreased with time since the last burn. Presence in the absence of gray squirrels suggests that southern fox squirrels are selecting habitats on BWPGC with respect to both resource needs and competition with gray squirrel. Additionally, my level-of-effort (LOE) analysis indicated that 7 consecutive days of camera trapping without a southern fox squirrel detection would provide 90% confidence of the species' absence in areas burned 2 or more years prior to sampling in southeastern Virginia. Further management for southern fox squirrels in the future should focus on high rotational (short fire return interval) burns in areas of savanna as well as pine-hardwood mixed areas and hardwood-pine savanna ecotones. / Master of Science / The southern fox squirrel (Sciurus niger niger) is a subspecies of fox squirrel that ranges from southeastern Virginia down to northern Florida. All throughout its range in the Southeast, southern fox squirrel habitat has been fragmented from natural mixed pine-hardwood woodland forests to agriculture and high rotation pine plantations. Additionally, habitat has been further transformed by the lack of prescribed fire as a management tool on the landscape. This has in turn created sparse and fragmented local populations of southern fox squirrels as well as possible competition with gray squirrels. Further, the southern fox squirrel has not been studied in Virginia in over 20 years and management recommendations are lacking. I studied the resource needs, occupancy, home range and competition of southern fox squirrels in two physiographic regions of Virginia: the Coastal Plain and Piedmont regions. The Coastal Plain field site was Big Woods Wildlife Management Area and The Nature Conservancy's Piney Grove- both adjacent to each other. The Piedmont field site was Military Training Center Fort Barfoot. Here I utilized camera trapping, nest box monitoring, live trapping, and radio tracking to assess the resources they are utilizing in each area through home range analyses. I found that southern fox squirrels are selecting areas that have low fire return intervals and are located in pine savanna habitats. Therefore, fire should be prioritized as a management tool for southern fox squirrel habitat in pine savanna areas. I also used camera trapping data to identify the possible competition among gray and fox squirrels and fox squirrel detection through occupancy modeling. My findings reflected that there is apparent competition between southern fox squirrels and eastern gray squirrels and that southern fox squirrels are selecting heavily burned areas not only for their resource needs, but also because gray squirrels are absent. I concluded through my studies that the southern fox squirrel currently occupies southeastern Virginia, particularly in the Coastal Plain, however at low numbers. This could be due to suitable habitat on Big Woods/Piney Grove, but the surrounding habitat is of marginal quality. Further, in documenting southern fox squirrels, multi day camera surveys in mixed pine-hardwood woodland and pine savannas should be prioritized. Also, in aims to increase the presence of southern fox squirrels on the landscape, short rotation prescribed burning should be prioritized as well as additionally considering meditation among gray squirrel and fox squirrel competition.

Habitat modeling can assist in managing potentially widespread but poorly known biological resources such as the federally endangered Delmarva fox squirrel (DFS; Sciurus niger cinereus). The ability to predict or identify suitable habitat is a necessary component of this species' recovery. Habitat identification is also an important consideration when evaluating impacts of land development on this species distribution, which is limited to the Delmarva Peninsula. The goal of this study was to build a predictive model of DFS occurrence that can be used towards the effective management of this species. I developed 5 a'priori global models to predict DFS occurrence based on literature review, past models, and professional experience. I used infrared photomonitors to document habitat use of Delmarva fox squirrels at 27 of 86 sites in the southern Maryland portion of the Delmarva Peninsula. All data were collected on the U.S. Fish and Wildlife Service Chesapeake Marshlands National Wildlife Refuge in Dorchester County, Maryland. Preliminary analyses of 27 DFS present (P) and 59 DFS absent (A) sites suggested that DFS use in my study area was significantly (Wilcoxon Mann-Whitney, P < 0.10) correlated with tree stems > 50 cm dbh/ha (Pmean = 16 + 3.8, Amean = 8+ 2.2), tree stems > 40 cm dbh/ha (Pmean = 49 + 8.1, Amean = 33 + 5.5), understory height (Pmean = 11 m + 0.8, Amean = 9 m + 0.5), overstory canopy height (Pmean = 31 m + 0.6, Amean = 28 m + 0.6), percent overstory cover (Pmean = 82 + 3.9, Amean = 73 + 3.1), shrub stems/ha (Pmean = 8068 + 3218, Amean = 11,119 + 2189), and distance from agricultural fields (Pmean = 964 m + 10, Amean = 1308 m + 103). Chi-square analysis indicated a correlation with shrub evenness (observed on 7% of DFS present sites and 21% of DFS absent sites). Using logistic regression and the Information Theoretic approach, I developed 7 model sets (5 a priori and 2 post hoc) to predict the probability of Delmarva fox squirrel habitat use as a function of micro- and macro-habitat characteristics. Of over 200 total model arrays tested, the model that fit the statistical, biological, and pragmatic criteria postulated was a post hoc integrated model: DFS use = percent overstory cover + shrub evenness + overstory canopy height. This model was determined to be the best of its subset (wi = 0.54), had a high percent concordance (>75%), a significant likelihood ratio (P = 0.0015), and the lowest AICc value (98.3) observed. Employing this predictive model of Delmarva fox squirrel occurrence can benefit recovery and consultation processes by facilitating systematic rangewide survey efforts and simplifying site screenings. / Master of Science