CRL: General Conservation Projects - Species Of Concern

CRL: Conservation Projects - Species Of Concern


Differential Response of a Native Arizona Gray Squirrel and an Introduced Abert’s Squirrel to a Mosaic of Burn Severities
  • Time Period: August 2011-Present

  • Student: Shari Ketcham

  • Location: Santa Catalina Mountains, AZ, U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions: What burn severities do tree squirrels use post fire regarding resources such as dreys, cavities, and food? How large are the patch sizes of the burn severities that tree squirrels choose to use? Are there any competition factors between tree squirrels for resources post fire? If so, what resources do tree squirrels compete for? What is the estimated abundance and distribution of tree squirrels on the Santa Catalina Mountains?




  • Major Findings: NA-Research in Progress


Space Use, Sociality, and Foraging Ecology of Antelope Jackrabbits
  • Time Period: May 2013-Present

  • Student: Maria Altemus

  • Location: Southeastern Arizona, U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions: The antelope jackrabbit (Lepus alleni) is a large hare found in southern Arizona south into Mexico that has not been intensely studied and about which little is known.  Early studies on antelope jackrabbits were conducted in the 1930’s, in relation to cattle grazing, but since then, very little has been published about these secretive and fast animals.  Antelope jackrabbits are so called because their white rump is displayed when they flee, similar to the pronghorn (Antilocapra americana).  These animals inhabit the shrubby grasslands that span the U.S.-Mexico border.  They are uniquely adapted to their desert environment, as they do not require free water to survive, but instead rely on their food sources (such as mesquite and succulents) and physiological specializations to persist.  One food that these animals eat is the fruit of the Pima pineapple cactus (Coryphantha scheeri var. robustispina).  This cactus is listed as endangered by the U.S. Fish and Wildlife Service as endangered and it is therefore important to learn about the ecology of this plant as well as the animals that depend on it. 


  • Through my research, I am hoping to examine more closely at the social structure and behavior of antelope jackrabbits, as they are sometimes seen in groups of up to 5 or 6.  I also hope to place radio or GPS collars on animals, as this has never been done, and learn more about habitat use and territoriality.   This aspect of my research will tie in with antelope jackrabbit’s use of Pima pineapple cactus and their role in the seed dispersal of this endangered cactus. 


  • Major Findings: NA-Research in Progress


Effects of Re-establishing Black-tailed Prairie Dog Colonies on Southeastern Arizona Grasslands
  • Time Period: January 2011-Present

  • Student: Sarah Hale

  • Location: Las Cienegas National Conservation Area, AZ, U.S.A

  • Project Details (click to expand/reduce)
  • The loss of biodiversity can have profound effects on an ecosystem, especially when a species lost is important to that ecosystem. The keystone species concept was introduced over 40 years ago, by Paine, referring to the role of the starfish Pisaster ochraceus and tritons Charonia spp. in the marine littoral zone (Paine 1969, Mills et al. 1993). A keystone species is exceptionally important in maintaining the organization and diversity of their community (Mills et al. 1993), and has been defined as a species whose impact on its community or ecosystem is large, and disproportionately large relative to its abundance (Power et al. 1996).

  • The black-tailed prairie dog (BTPD: Cynomys ludovicianus) is considered a keystone species, and was extirpated by humans from its historical range in Arizona by 1960. The BTPD is seen as a pest by many people, but these ecosystem engineers provide burrows for other species (e.g. burrowing owls [Athene cunicularia] and rattlesnakes [Crotalus sp.]), excavate nutrient rich soil that, in turn, provides rich vegetation for grazers, and serve as a food source for many carnivores and birds of prey. Between 2008 and 2011 Arizona Game and Fish Department translocated approximately 380 BTPDs from New Mexico and Sonora to 3 sites at Las Cienegas National Conservation Area in southeastern Arizona to improve grassland health and increase species diversity within the BTPDs’ historical range. In 2012 a fourth site was populated with prairie dogs from Las Cienegas.

  • Research Questions: 1) Why do colonies exhibit the survival and reproductive rates observed? 2) What is the fate of dispersers, and why do certain individuals disperse from colonies? 3) Do translocated BTPDs establish a role as a keystone species? My results will provide important information for future management decisions, reduce human-prairie dog conflicts by documenting the impacts of their presence, assess their keystone species status, and provide information about where to introduce new colonies.


Competition between native and introduced species
  • Time period: August 2010 – present

  • Student: Jonathan J. Derbridge

  • Location: Pinaleño Mountains, Arizona, USA

  • Project Details (click to expand/reduce)
  • Major Questions: I am studying mechanisms of competition between native and introduced species. Exploitation competition occurs when individuals have indirect negative effects on other individuals by restricting access to a common resource. Competition from introduced species for common food resources may force native species to forage more widely, and consume sub-optimal diets. Isolated populations of territorial species may, over time, become less adept at excluding ecologically similar competitors. I am using experimental removals of introduced Abert’s squirrels (Sciurus aberti) to test hypotheses on the impacts of dietary and spatial overlap with the Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis). I am also conducting tests of exploitation competition that relate to the relative abilities of an invader to succeed, and a native species to maintain its advantage. These tests include examining how Abert’s squirrels may take advantage of larder-hoarding by red squirrels, and comparing territorial behavior of Mount Graham red squirrels with individuals in other red squirrel populations.

  • Research Questions: What are the impacts of dietary overlap between native and introduced species occupying similar niches? Does syntopy with an introduced species incur fitness costs associated with changes in home range size and composition for native species? Do introduced non-hoarding species compete with larder-hoarding native species through kleptoparasitism? Does isolation from interspecific competition lead to weakening of territorial behavior and facilitate successful invasions?


Proximate cues and ultimate consequences for natal dispersal and settlement in an altered forest landscape: influence of experience, behavior, and habitat
  • Time Period: May 2010 - Present

  • Student: Melissa Merrick

  • Location: The Pinaleño Mountains, AZ, U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions: I am interested in factors influencing animal movements and habitat selection in the face of landscape alteration and fragmentation. Movement via natal dispersal is an important ecological mechanism contributing to gene flow, population structure and population dynamics, and guards populations against local extinction. Natal dispersal includes three stages: emigration, transience and exploration, and immigration and settlement. Whether an individual disperses, if it disperses how far it travels, how many places it explores, and where it settles is highly variable and is conditioned upon many factors including individual condition, local population density, sex ratios, resource abundance, experience in the natal area, habitat fragmentation, and individual behavior differences. Previous studies have shown that experience in the natal area provides individuals with important habitat cues which aid in deciding upon where to settle and also leads to variation in settlement patterns. Individual behavior differences may play a role in dispersal distance and settlement decisions, including decision rules individuals employ when selecting a place to settle. Local density of conspecifics and associated sex ratios may influence male settlement decisions, whereas female settlement decisions may be more driven by available food resources. Increasingly, habitat fragmentation is also becoming an external factor influencing dispersal decisions and evidence suggests that small mammals dispersing through a fragmented habitat matrix tend to disperse further and explore less than individuals in contiguous habitat. I am testing several hypotheses related to natal habitat preference induction, behavioral phenotypes, decision rules, and habitat fragmentation and their influence on natal dispersal, especially transience and immigration.

  • Some of my main research questions include: Do natal habitat cues (e.g. habitat structure, associated microclimate, and food availability) influence where settlement occurs? Do individual behavior differences (behavioral phenotypes) influence exploratory movements, decision rules, dispersal distance, and survival? Does forest fragmentation influence decision rules, settlement choices, and survivorship?

  • Major Findings To Date: Compared to non-peripheral red squirrel populations, dispersal in MGRS is sex-biased and exploration movements and settlement distances are far greater. Individual behavior differences explain variation in dispersal distances - active, aggressive individuals tend to disperse longer distances compared to less active, docile individuals. Natal habitat structure may play a role in cueing dispersers in on locations in which to settle. Forest structure derived from remotely sensed LiDAR data (e.g. canopy cover, basal area of live trees) in an individual’s natal area is more similar to forest structure at an individual’s settlement location compared to random locations. Further analyses are underway.


Road and traffic effects on movements and space use of red squirrels
  • Time Period: 2009 - present

  • Student: Hsiang Ling Chen

  • Location: Mt. Graham, AZ, U.S.A.

  • Project Details (click to expand/reduce)
  • Road ecology is a burgeoning field of inquiry as roadways expand in number, length and width. We know that roads fragment habitats, increase mortality, change microclimates, and can act as barriers…thus they present a challenge in the conservation of biodiversity. Roads may function as impermeable barriers to some species while being semi-permeable to others. We are examining the relative permeability of roads to two species in the Pinaleno Mountains of southeastern Arizona: federally endangered Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis) and non-native Aberts squirrels (Sciurus aberti).

  • Major Questions: Do red squirrels avoid roads? If so, what factors are most influential to avoidance? Do they avoid forest edges created by roads, forest gaps, or traffic disturbances?


Competition for conifer cones as a potential mechanism of endangerment for the Mt. Graham red squirrel.
  • Time Period: 2007 - 2010

  • Student: Rebecca Minor

  • Location: Pinaleño (Graham) Mountains, Graham County, southeastern Arizona (Coronado National Forest).

  • Project Details (click to expand/reduce)
  • Major Questions/Objectives: Non-native species are a major cause of endangerment for native species, but the mechanisms are often unclear. The sky island region of the southwestern US and northwestern Mexico supports many isolated endemic species that are restricted to high elevation forests and vulnerable to species invasions. One such range, the Pinaleño Mountains in southeastern Arizona, supports the entire population of the critically endangered Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) (MGRS). A second tree species, the Abert’s squirrel (Sciurus aberti) was introduced to the range in 1941 by Arizona Game and Fish Department for increased recreational hunting opportunities. Our field experiment quantified the impact of introduced Abert's squirrels on rates of food removal within the range of the MGRS. We placed single cones on 4m x 4m plots (1m spacing) at random locations in the forest and observed the rate of removal by both species of squirrel through direct observation and remote cameras. Then Abert’s squirrels were excluded from cone removal by placing cones in wire mesh tubes that were of small diameter, so that only MGRS could enter. burn severity? Does the landscape pattern (patchiness) of burn severity affect squirrel habitat use?

  • Major Findings: In the presence of Abert's squirrels, the time until 50% of cones were removed was significantly faster than when Abert's squirrels were excluded. The impact on food availability as a result of cone removal by Abert's squirrels suggests the potential of food competition as a mechanism of endangerment for the Mount Graham red squirrel. We suggest that a successful management approach for MGRS with target the impact of Abert’s squirrels on food availability. That a large proportion of cones available to both MGRS and Abert’s squirrels were removed before cones available only to MGRS suggests the importance of considering removal of the introduced Abert’s squirrel as a priority in conserving red squirrels in the Pinaleño Mountains.


Factors influencing habitat use by wildlife relative to landscape disturbance
  • Time Period: August, 2006 – December, 2010

  • Student: Sandy Doumas

  • Location: The Chiricahua Mountains, AZ, U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions: I am interested in factors influencing habitat use by wildlife relative to landscape disturbance, especially fire. Fire is a necessary and recurring disturbance in many ecosystems with profound effects over time on vegetation composition, structure, and landscape pattern. The effects of fire on ecosystems have been complicated by decades of fire suppression followed by reintroduction of fire into fire-deprived ecosystems. Historically, fire-adapted forests were relatively resilient to fire, and some current forest management techniques seek to restore forests to historical composition, structure, and landscape pattern to recreate fire-resiliency. I study habitat use by native wildlife to better understand the response of wildlife to alterations of vegetation structure and pattern following the reintroduction of fire. Specifically, I study habitat use of the Mexican fox squirrel, Sciurus nayaritensis chiricahuae, in conifer forests of the Chiricahua Mountains of SE Arizona, which have experienced several recent fires.

  • Some of my main research questions include: Does burn severity of recent fires and vegetation structure affect squirrel habitat use? How are the vegetation characteristics most important to habitat use related to burn severity? Does the landscape pattern (patchiness) of burn severity affect squirrel habitat use?

  • Major Findings: To Date: Mexican fox squirrels feed in forest with open understory and closed canopy cover. Vegetation within home ranges of squirrels is characterized by lower understory density, consistent with the effects of low-severity fire, and larger trees than random locations. These results suggest that return of low-severity fire can help restore habitat for Mexican fox squirrels and other native wildlife species with similar habitat affiliations in forests with a historical regime of frequent, low-severity fire. Habitat use by Mexican fox squirrels is positively associated with moderate burn heterogeneity, suggesting that small areas of severe burn incorporated within low-severity burn may be beneficial to Mexican fox squirrels and other native wildlife species.


Ecology of Neotropical Tree Squirrels
  • Time Period: May – July 2009 and June – July 2010

  • Student: Rosa Jessen

  • Location: Area de Conservacion Regional Tamshiyacu-Tahuayo, Loreto, Peru

  • Project Details (click to expand/reduce)
  • Major Questions: Does vegetation type affect density and habitat use of neotropical tree squirrels? What vegetation characteristics are influential to rainforest squirrels? What is the mammalian diversity associated with neotropical tree squirrels?

  • Rainforests are home to the greatest mammal diversity, but little is known about most of the rainforest species. Small mammals in the rainforest play important roles, providing ecological services such as seed dispersal and pollination. These species also drive the dynamics and complexity of biological communities by serving as predators and providing a prey base for a range of rainforest species. The Amazon Basin contains one of the world’s largest rainforests, much of which is found in Peru. Five species of tree squirrels are found in the Peruvian Amazon: northern Amazon red squirrel (Sciurus igniventris), southern Amazon red squirrel (S. spadiceus), Bolivian squirrel (S. ignitus), Amazon dwarf squirrel (Microsciurus flaviventer) and neotropical pygmy squirrel (Sciurillus pusillus) but there is a great lack of knowledge of neotropical tree squirrels and no one has examined their role in rainforests. Little is known about life history, ecological interactions, and distribution of these squirrels.


Response of the Mount Graham Red Squirrel (Tamiasciurus hudsonicus grahamensis) to Postfire Conditions
  • Time Period: 2006-2007 (field work) 2008-2012 (data analysis, writing, publication)

  • Student: Seafha Tuttle (Blount)

  • Location:Mt. Graham, AZ, U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions/Objectives: Our main objectives were to assess space use of Mount Graham red squirrels, vegetation characteristics associated with middens, and continued occupancy of middens, mountain-wide, by Mount Graham red squirrels in areas of various burn severity.

  • Major Findings: A main effect of season on both size of home ranges and core areas was apparent. No main effect of burn severity on size of home range or size of core area was detected. Slope, canopy cover, burn severity, and aspect were important variables for distinguishing middens from random locations. Dead trees, aspect, and total number of trees were important for distinguishing between occupied and unoccupied middens. Mountainwide, occupancy of middens was influenced by burn severity of middens and surrounding vegetation. Also, unburned middens were occupied more continuously than burned middens.

  • Citation: Blount and Koprowski. 2012. Response of the Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) to postfire conditions. The Southwestern Naturalist 57(1):8-15


What can endemics tell us? Space use and ecology of the endemic Arizona gray squirrel
  • Time period: August 2006 – December 2009

  • Student: Nichole Cudworth

  • Location: Huachuca Mountains, Arizona, USA

  • Project Details (click to expand/reduce)
  • Research questions: How does mating strategy influence the space use of Arizona gray squirrels? At what scale are Arizona gray squirrels selecting nest sites?

  • Major findings: Parental investment often differs between the sexes. For mammals, females invest heavily in reproduction, due to the high costs of pregnancy and lactation. Consequently, fitness of females is likely limited by the availability of food. Fitness of males, however, is more likely limited by the availability of mates. We investigated how these limiting factors would be predicted to influence the space use of Arizona gray squirrels. Arizona gray squirrels do not defend territories, and a female will only enter estrus for one day throughout the breeding season, thereby significantly reducing mating opportunities for males. We found that home ranges of Arizona gray squirrels are large (59 ha) and vary between sexes and seasons. Males had larger home ranges than females overall, and males increased home-range sizes during the breeding season, when males were traveling greater distances to locate receptive females. Females, however, maintained relatively constant home-range sizes throughout the year, although these home ranges were still large compared to other, closely related species, suggesting a system in which food availability is likely patchy and variable.

  • Tree squirrels are highly dependent upon nests to provide a place to rest, raise young, avoid predators, and escape inclement weather. However, the scale at which nest-site selection has been analyzed has not been consistent, despite the obvious management implications when designing habitat plans. Arizona gray squirrels use leaf nests, or dreys, extensively throughout the year. We evaluated nest-site selection at 4 spatial scales: forest-type, nest-site, nest-tree, and within-canopy placement. Arizona gray squirrels select nesting locations within all spatial scales, although the benefits provided within these spatial scales likely varies, including providing access to food and water, cover from predators, travel routes to and from nest trees, thermal protection, and stable nesting structures. Riparian areas and the availability of Arizona sycamores (Platanus wrighti) for nest sites were especially important, emphasizing the need to protect these unique forest types in the mountains of the southwestern United States.


Ecology of the endemic Mearns’s squirrel (Tamiasciurus mearnsi) in Baja California, Mexico
  • Time Period: August 2004 – May 2008

  • Students: Nicolas Ramos-Lara

  • Location: Sierra de San Pedro Mártir, Baja California, Mexico

  • Project Details (click to expand/reduce)
  • Major Questions: 1. What is the current situation of the arboreal squirrels of Mexico (review chapter) 2. Do Mearns’s squirrels have specific habitat requirements for nesting? 3. Do home-range dynamics and habitat use of Mearns’s squirrels differ from other congeners? 4. Do life-history and behavioral tactics of Mearns’s squirrels differ from other congeners?

  • Major Findings: 1. In Mexico, there are 14 recognized species of arboreal squirrels of which four are endemic, with the states of Chiapas and San Luis Potosi possessing the greatest diversity. 2. Presently, all species are listed under some category of risk by IUCN, seven by Mexico’s SEMARNAT, and only one by CITES. 3. Our literature survey yielded 37 publications revealing that a dearth of scientific information still exists on the arboreal squirrels of Mexico. 4. States with a greater diversity of arboreal squirrels also have higher annual wood productions, which may pose a serious threat to their persistence. 5. Mearns’s squirrels rely primarily on tree cavities for nests, with nest tree species, nest tree condition, nest tree size (DBH), canopy cover, and occurrence of white firs (Abies concolor) as important characteristics of the habitat for nesting. 6. Without larderhoards (middens), home-range dynamics of Mearns’s squirrels are similar to nonterritorial squirrels of the genus Sciurus, suggesting that middens played an important role in the evolution of territoriality in Tamiasciurus. 7. Using satellite imagery, I found that remote areas in the Sierra de San Pedro Mártir appear to have suitable habitat for the species. 8. Survival of adult Mearns’s squirrels was influenced by sex and body mass. 9. Mearns’s squirrels are heavier and apparently also larger than other congeners, possibly in part as an adaptation to feed on large pine cones (Pinus). 10. Interyear variation in weather and food supply strongly influenced fitness-related traits and behavior of Mearns’s squirrels.


Differential response to fire by an exotic and an endemic species complicate endangered species conservation
  • Time Period: May 2006 to Oct 2007

  • Student: Nate Gwinn

  • Location: Mount Graham (Pinaleño Mountains), Graham County, Arizona, USA

  • Project Details (click to expand/reduce)
  • Major Questions: The Nuttall Complex fire burned ~ 12029 ha in the Pinaleño Mountains of southeastern Arizona in summer 2004, including large areas of the upper elevation mixed conifer and spruce fir forests. Historically, mixed conifer forests in the Pinaleños experienced a low severity fire every 4 to 6 years, and spruce-fir forests experienced infrequent stand-replacement burns every 300 years. To investigate the effect of wildfire on exotic and introduced species, we looked at the differential use of burned and unburned areas by introduced Abert’s squirrels and the endemic and critically endangered Mount Graham red squirrel in the Pinaleños. We assessed effects of wildfire on habitat use of introduced Abert’s squirrels and native red squirrels by sampling species-specific feeding sign and employing radiotelemetry to reveal use of burned and unburned areas by both species. We document differential use of fire-impacted habitats that favors the introduced species thus complicating traditional conservation efforts used in forested environments.



  • Major Findings: Our study is the first to document the positive response of an exotic mammal and negative response of the native species to wildfire and suggests that fire must be used judiciously as a restoration tool. Abert’s squirrels thrive in mixed conifer forest, our study documented that Abert’s squirrels fed, moved and nested within mixed conifer forest affected by wildfire. Home ranges of Abert’s squirrels were smaller in burned than in unburned forest. This suggests that habitat created by wildfire was of higher quality than unburned areas. Abert’s squirrels selected sites that had more live trees, less logs, and higher canopy closure than random sites within the burned area, similar to characteristics of mature ponderosa pine forests that Abert’s squirrels prefer in native range. These characteristics include high basal area, mature trees with interlocking crowns, and an understory with little down and woody debris. Transect data on feeding sign also indicated that Abert’s squirrels remained in burned areas. In effect, wildfire may be improving habitat for Abert’s squirrels in mixed conifer forest by creating preferred structure.



Variation among red squirrel populations: Ecological differences at the edge of their range and response to fire.
  • Time Period: 2004 - 2006

  • Student: Katharine M. Leonard

  • Location: Pinaleño (Graham) Mountains, Graham County, southeastern Arizona (Coronado National Forest). White Mountains, Greenlee County, east-central Arizona (Apache-Sitgreaves National Forest).

  • Project Details (click to expand/reduce)
  • Major Questions/Objectives: Populations at the edge of their geographic range may inhabit areas with different habitat structure and resources than central populations, and thus may differ in population dynamics. Understanding these unique characteristics is especially important for populations of high conservation priority, such as the endangered Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis). The Mt. Graham red squirrel (MGRS) is endemic to southeastern Arizona, represents the southernmost red squirrel population and is found at lower densities than conspecifics in the center of the range. To determine if differences are due to conditions at the southern periphery of the range, we compared habitat characteristics, demography, body mass, space use and nesting behavior with another subspecies located at the southern edge of the range, the Mogollon red squirrel (T. h. mogollonensis). In addition, we studied demography and behavior of MGRS inhabiting areas within and outside areas of low-intensity burn following the Nuttall fire complex in the Pinaleño Mountains (summer 2004).

  • Major Findings: We found that mean and minimum daily temperatures were higher at Mt. Graham whereas maximum temperatures were higher in the White Mountains, male Mogollon red squirrels were heavier than male Mt. Graham red squirrels in all seasons and female Mogollon red squirrels were slightly heavier than female Mt. Graham red squirrels in spring, proportion of squirrels in reproductive condition was lower in female Mogollon red squirrels, Mogollon red squirrels had smaller home ranges, used different types of nests and traveled less distance to nest than Mt. Graham red squirrels. There were no differences in annual rainfall, seedfall, habitat characteristics or survival between mountain ranges. Localized conditions appear to account for the disparity between populations. These differences demonstrate the importance of evaluating attributes of peripheral populations for maximizing persistence and intraspecific diversity.

  • Upon examining MGRS physical and behavioral traits between areas of no burn and low-intensity burn from the 2004 Nuttall fire, we found that body mass, proportion of individuals in reproductive condition, and distance squirrels traveled to nest did not differ between squirrels within and outside the perimeter of the fire. Within the perimeter, red squirrels had smaller home ranges and shifted territories less frequently and had shorter distances from their previously held territories than squirrels outside the perimeter. Mount Graham red squirrels evolved with patchy, low-intensity fires like those that burned in mixed-conifer forests in the Pinaleño Mountains and may be able to persist in areas affected by this level of disturbance.


Forest disturbance and the long term population persistence of the Mt. Graham red squirrel:  a spatially explicit modeling approach
  • Time Period: 2002 - 2006

  • Student: David Wood

  • Location: Pinaleño (Graham) Mountains, Graham County, southeastern Arizona.  (Coronado National Forest), U.S.A.

  • Project Details (click to expand/reduce)
  • Major Questions: Difficulties in conservation and management of forest ecosystems arise from dynamics of forests and challenges in understanding disturbance. Disturbances, especially fire and insect outbreaks, have increased in occurrence and severity due to climate change and forest management. 
    The Pinaleño Mountains of southeastern Arizona, USA have suffered catastrophic fire and large scale insect outbreaks in the last decade and are the only home of the federally endangered Mt. Graham red squirrel (MGRS:  Tamiasciurus hudsonicus grahamensis), therefore an understanding the impacts of forest disturbances on population dynamics is critical for conservation of this fragile species. We sought to develop and a spatially explicit population model to predict long-term population dynamics of MGRS and to combine this model with life-history data and high-resolution satellite imagery with the goal of examining effects of future disturbances on the population.


  • Major Findings: We tested model predictions using available range-wide red squirrel life-history data from the literature and fieldwork specific to the MGRS. An input data set using general mean life history values overpredicted MGRS abundance. However, we found significant correlation with known squirrel abundance using a general data set with curtailed fecundity and survival. A model with MGRS-specific data provided the best fit to observed population size. We investigated potential impacts of two major threats to the MGRS: competition from introduced Abert’s squirrels (Sciurus aberti) and increased levels of predation. Predation and particularly competition could have significant effects on the future population of the MGRS. Careful attention must be used to model the viability of fringe populations as peripheral populations can have a different life history than populations found in the range core.


  • We also modeled potential Mt. Graham red squirrel habitat by identifying characteristics of cover surrounding their centrally defended larderhoards to assess effects of forest disturbance on habitat. We classified high spatial resolution satellite imagery into ground cover classes and used logistic regression to determine areas used by squirrels. We also used midden locations in conjunction with slope, elevation, and aspect variables to create a predictive habitat map for Mt. Graham red squirrels. Squirrels selected areas of denser forest with higher seedfall for midden sites. Among active middens, those in the densest and least damaged forests were occupied in more seasons than those in more fragmented and damaged areas. The future conservation of red squirrels and the return of healthy old-growth forests to the Pinaleño Mountains will rely on management in mixed conifer zones of the mountain and active restoration of highly damaged upper elevation spruce-fir forests to return them to squirrel habitat. This model allows us to evaluate the spectrum of fine- to coarse-scale disturbance effects (individual tree mortality to the area wide boundaries of a disturbance) with high-resolution satellite imagery.

  • Lastly, we combined our spatially explicit population model with the spatial models of habitat heterogeneity. We parameterized the model with estimates of extent, frequency, and severity of insect outbreaks and fire and used the number of Mt. Graham red squirrel populations dropping below critical population thresholds to characterize the effects of these disturbances. We determined future disturbances, even at low levels, are likely to have a detrimental effect on Mt. Graham red squirrel population size. This model framework can be used to predict effects of future disturbance on habitat quality and population persistence for species in general.


Suitability of Potential Habitat for the Extirpated Arizona Black-tailed Prairie Dog
  • Time Period: 2002 - 2005

  • Student: Carol A. Coates

  • Location: Las Cienegas National Conservation Area and Ft. Huachuca Military Base, AZ, USA Upper San Pedro River Valley, Ejido Morelos, Sonora, Mexico

  • Project Details (click to expand/reduce)
  • Major Questions/Objectives: Study objectives were: 1) to determine if areas identified as potential re-introduction sites were suitable to support BTPD populations by comparing habitat characteristics with an occupied BTPD colony in northern Sonora, Mexico, 2) assess what pre-release management actions may be required in these areas, and 3) determine whether the presence of prairie dogs could potentially affect avian grassland species diversity in Arizona.

  • Major Findings: There was considerable overlap in habitat variables between the occupied BTPD colony in Sonora and potential re-introduction sites in Arizona. However, greater densities of grass, shrubs, and trees were found on the potential sites Arizona sites than on the occupied Sonora colony. Though grass species diversity did not differ between the Arizona and Sonora sites, grass species diversity was much lower on the Ft. Huachuca site, mainly due to large amounts of introduced Lehmann lovegrass. Management actions needed on the Arizona sites to render them more suitable for BTPD introduction include mowing grass and decreasing shrub and tree densities possibly through use of prescribed fire.

  • Using fixed-radius point counts, avian species diversity was determined to be higher on the Arizona sites that on the Sonora sites. The greater number of avian species on the Arizona sites can be attributed to higher shrub densities and wider range of physical and environmental features, such as ephemeral streams and mesquite thickets. The reintroduction of BTPD on the Arizona sites would likely alter plant species composition and structure and, therefore, the abundance of avian species, especially those species requiring trees and shrubs for nesting and foraging. However, avian species that require open spaces, such as shrikes and larks, or the presence of abandoned small mammal burrows for nesting, such as the burrowing owl, may increase on the Arizona sites due to BTPD habitat management practices.

  • Based on the vegetation characteristics, proximity to land protected from development, and historical presence of BTPD, the Arizona sites appear to be suitable locations for re-introduction of BTPD. Pre-release habitat management, such as mowing and prescribed fire, as well as a more fine-scale assessment of specific release sites (especially soil characteristics) will be required before attempting to return Black-tailed prairie dogs to southern Arizona.


Space use, ecology, & conservation of Chiricahua fox squirrels
  • Time Period: 2001 - 2004

  • Student: Bret S. Pasch

  • Location: Chiricahua National Monument (National Park Service), Chiricahua Mountains, southeast of Willcox, Cochise County, Arizona.

  • Project Details (click to expand/reduce)
  • Major Questions/Objectives: Chiricahua fox squirrels (Sciurus nayaritensis chiricahuae) are endemic to the Chiricahua Mountains of southeastern Arizona. A paucity of natural history information and uncertain conservation status served as impetus for us to initiate a descriptive ecological study of the species. In addition, we examined the impacts of human suppression of fire on patterns of habitat use and survival of Chiricahua fox squirrels in fire-suppressed and fire-prescribed areas of the Chiricahua Mountains. We used radiotelemetry techniques to elucidate space and habitat use, survivorship, and fire impacts in our investigation.

  • Major Findings: We found that Chiricahua fox squirrels differed in several capacities from more widespread species of tree squirrels. Females had a mean of 1.6 (range 1-2) offspring per litter and we found an overall population density of 0.07/ha, both parameters lower than other North American tree squirrels. Seasonal fluctuations in body mass and space use generally paralleled other species of tree squirrels with some notable exceptions. Male Chiricahua fox squirrels maintained a fairly constant body mass and large home range size throughout the year, in contrast to other tree squirrel species that typically show a reduction in both measures in non-mating seasons. Extreme spatial and temporal fluctuations of food experienced by Chiricahua fox squirrels might result in annual patterns in space use and body mass that differ from tree squirrels living in forests with a greater abundance of food.

  • We found differences in habitat use and survival of squirrels in areas of the Chiricahua Mountains with differing fire regimes (suppressed vs. prescribed). Core areas of squirrels within fire-suppressed areas were larger and contained more understory shrubs than core areas of squirrels in fire-prescribed areas. Shrub cover and canopy heterogeneity influenced core-area size and distance traveled, and squirrels that were depredated traveled farther than conspecifics that survived, but shrub cover and canopy heterogeneity were not directly associated with squirrel survival. Suppression-induced increases in understory vegetation might force squirrels to travel greater distances to meet energetic requirements and thereby increase predation risk. Retention of mature forested canyons and restoration of natural fire regimes will be important for the persistence of Chiricahua fox squirrels.