conservation.arizona.edu - Abert’s squirrels

Differential response of native Arizona gray squirrels and introduced Abert's squirrels to a mosaic of burn severities

thackerk1 — Mon, 22 Jul 2019 21:22:42 +0000

Authors

Shari L. Ketcham

John L. Koprowski

Donald A. Falk

Disturbance events can alter habitat properties, leading to species displacement, isolation, and/or local extinction. Therefore, understanding the interactions of potential ecological drivers on native and introduced wildlife species post-fire is critical to understand influences on distribution. We studied native Arizona gray squirrels (Sciurus arizonensis), which are believed to favor dense riparian habitat, and introduced Abert’s squirrels (S. aberti), which prefer open ponderosa pine (Pinus ponderosa) forests. We examined how uncommon native Arizona gray squirrels and introduced Abert’s squirrels used areas previously burned by widespread fires more than a decade prior to our study. To determine how past fire may affect squirrel habitat, we examined squirrel use and occupancy within fire altered habitats and used distance sampling to determine squirrel distribution, feeding, and nest use within a mosaic of burn severities. Occupancy and habitat use indicated that introduced Abert’s squirrels readily used post-fire conditions more than native Arizona gray squirrels, likely due to the opening of a dense understory. Arizona gray squirrels remained in unburned riparian areas; therefore, fire affected riparian areas can be directly targeted for management to increase abundance of the native species.

Additional Information

Mammal Study 42:247-258.

Date of publication:

2017

Topics

Arizona gray squirrel

Abert’s squirrels

ponderosa pine

wildfire effects

occupancy

habitat

feeding signs

dreys

Research Categories

Disturbance Ecology Sky Islands Threatened and Endangered Species

Differential response to fire by an introduced and an endemic species complicates endangered species conservation

thackerk1 — Thu, 27 Jun 2019 22:58:10 +0000

Authors

R. Nathan Gwinn

John L. Koprowski

Fire is a natural component of, and serves as a tool for, the restoration of forested ecosystems worldwide; however, disturbance due to fire also has been implicated in the proliferation of invasive species. How these fires affect occupancy and use of the forest by wildlife is of great concern, in particular, the differential response of non-native and native species. In the North American Southwest, prior to European settlement, frequent wildfires helped to maintain forest structure. We examined the effect of a large wildfire on an introduced population of the Abert’s squirrel (Sciurus aberti) that has invaded the high elevation forests inhabited by the critically endangered Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis). We found that introduced Abert’s squirrels were more common than native red squirrels in burned areas. Abert’s squirrels did not abandon burned areas but nested, foraged, and did not adjust their home range size in burned areas. This suggests that invasive Abert’s squirrels are better able to exploit burned areas than native red squirrels and that fire can favor non-native species. This interaction between non-native species, native species, and fire adds new insight into the complexities of conservation and restoration of ecosystems and helps to inform conservation activities worldwide.

Additional Information

Hystrix

Date of publication:

2016

Topics

Mount Graham Red Squirrel

Abert’s squirrels

non-native species

invasive species

fire

Research Categories

Disturbance Ecology Sky Islands Spatial Ecology Threatened and Endangered Species

Low survival, high predation pressure present conservation challenges for an endangered endemic forest mammal

thackerk1 — Thu, 27 Jun 2019 22:19:15 +0000

Authors

Emily A. Goldstein

Melissa J. Merrick

John L. Koprowski

Knowledge of which population parameters and mortality risks contribute most to population decline and endangerment is necessary to develop informed and actionable conservation plans for threatened and endangered species (Rushton et al., 2006). The federally endangered Mount Graham red squirrel (Tamiasciurus fremonti grahamensis) is restricted to the Pinaleño Mountains, in southeastern Arizona, USA. The population is critically threatened with extensive habitat loss from fire as well as by an introduced non-native squirrel species, the Abert's squirrel (Sciurus aberti). Recovery is challenged by low survival and poor reproduction, such that the subspecies is functionally semelparous. We calculate survival rates and cause-specific mortality hazards from known-fate individuals to understand the impact of predation on survival and demography in this peripheral population. We document the lowest survival and highest rates of mortality in any population of North American red squirrels in both adult and juvenile age classes (mean annual survival: adults = 0.32, juveniles = 0.26). We attributed the majority of confirmed deaths to avian predation (adults 65%, juveniles 75%), and the daily hazard rate for avian predation was 15 times higher than for mammalian predation and 2 times higher than death from unknown causes. It is likely that the presence of an ecologically similar, non-native tree squirrel subsidizes a diverse avian predator guild, which includes two raptor species of conservation concern. In addition to efforts to remove the non-native Abert's squirrel, we recommend immediate forest restoration efforts in the long term, and habitat augmentation to increase structural complexity, cover, shelter, and food resources in the short term.

Additional Information

Biological Conservation

Date of publication:

2018

Topics

cause-specific morality

Mount Graham Red Squirrel

Abert’s squirrels

apparent competition

peripheral population

Research Categories

Population Ecology Sky Islands Threatened and Endangered Species

Edelman, A. J. and J. L. Koprowski. 2005. Diet and tree use of Abert's squirrels (Sciurus aberti) in a mixed-conifer forest. The Southwestern Naturalist 50(4): 461-465.

thackerk1 — Thu, 27 Jun 2019 20:58:17 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Abert’s squirrels (Sciurus aberti) are reported to be dependent on ponderosa pine (Pinus ponderosa) forests for food, cover, and nest sites. Introduced Abert’s squirrels in the Pinaleño Mountains of Arizona, however, occupy forests that contain little to no ponderosa pine. We documented diet and tree use of Abert’s squirrels in mixed-conifer forests of the Pinaleño Mountains using observations of marked animals. Individuals ate similar food items as Abert’s squirrels in ponderosa pine forests, including seeds, inner bark, buds, and fungi, but 5 conifer species were used as food sources. Douglas-fir (Pseudotsuga menziesii) and southwestern white pine (Pinus strob- iformis) were the most frequently eaten conifer species. Abert’s squirrels also were observed in all tree species. Our results suggest that the dependence of Abert’s squirrels on ponderosa pine is not as strong as previously reported.

Additional Information

DIET AND TREE USE OF ABERT'S SQUIRRELS (SCIURUS ABERTI) IN A MIXED-CONIFER FOREST

Date of publication:

2005

Topics

Abert’s squirrels

mixed-conifer forests

Pinaleño Mountains

diet

nest sites

Edelman, A. J., J. L. Koprowski, and J. L. Edelman. 2005. Kleptoparasitic behavior and species richness at Mt. Graham red squirrel middens. USDA Forest Service Proceedings RMRS-P-36: 395 - 398.

thackerk1 — Tue, 25 Jun 2019 01:31:05 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Jennifer L. Edelman

We used remote photography to assess the frequency of inter- and intra-specific klepto- parasitism and species richness at Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis) middens. Remote cameras and conifer cones were placed at occupied and unoccupied middens, and random sites. Species richness of small mammals was higher at red squirrel middens than random sites. Abert’s squirrels, potential kleptoparasites, were recorded only at unoccupied mid- dens and random sites. Non-resident red squirrels were most common at unoccupied middens and rare at occupied middens and random sites. Inter- and intra-specific kleptoparasitism of red squirrel middens appears uncommon likely due to territorial behavior.

Additional Information

Kleptoparasitic Behavior and Species Richness at Mt. Graham Red Squirrel Middens

Date of publication:

2005

Topics

Mount Graham Red Squirrel

kleptoparasitism

inter-specific

intra-specific

conifer cones

small mammals

middens

Abert’s squirrels

territorial behavior

species richness

Edelman, A. J. and J. L. Koprowski. 2005. Selection of drey sites by Abert's squirrels in an introduced population. Journal of Mammalogy 86(6): 1220-1226.

thackerk1 — Tue, 25 Jun 2019 01:24:39 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Abert’s squirrels (Sciurus aberti) are reported to depend on ponderosa pine (Pinus ponderosa) for food and nest sites. Introduced Abert’s squirrels in the Pinaleño Mountains of Arizona, however, occupy mixed-conifer forests that contain almost no ponderosa pine (about 2%). We examined selection of drey sites in this introduced population. Dreys (i.e., spherical nests) were built adjacent to the trunk at 75% of the tree height. Dreys were found in 5 different conifer species and ,2% were in ponderosa pine. Drey trees were larger and had more access routes than did random trees. Drey sites were steeper, had more large trees, Douglas-fir (Pseudotsuga menziesii), and southwestern white pine (Pinus strobiformis), and less corkbark fir (Abies lasiocarpa var. arizonica) than random sites. The structural characteristics of drey trees in the Pinalen ̃os population also were very similar to drey trees used by natural populations of Abert’s squirrels in ponderosa pine forests. Our results suggest that the dependence of Abert’s squirrels on ponderosa pine is not as strong as previously reported. Structural features such as tree size and access routes appear to be more important to selection of drey sites than tree species.

Additional Information

Selection of Drey Sites by Abert's Squirrels in an Introduced Population

Date of publication:

2005

Topics

Mount Graham Red Squirrel

Abert’s squirrels

nest-site selection

Pinaleño Mountains

exotic species

bolus nest

tassel-eared squirrel

obligate

Edelman, A. J. and J. L. Koprowski. 2006. Characteristics of Abert's squirrel (Sciurus aberti) cavity nests. The Southwestern Naturalist 51(1): 64-70.

thackerk1 — Tue, 25 Jun 2019 01:18:08 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Cavity nests are rarely used by Abert's squirrels (Sciurus aberti) in ponderosa pine (Pinus ponderosa) forests. Introduced Abert's squirrels in the Pinaleño Mountains of Arizona, however, exhibit occasional use of cavity nests (ca. 10%). We examined characteristics of cavity nest sites in this introduced population. Cavity nests were located at two-thirds of the tree height and were found mainly in both dead and live aspen (Populus tremuloides). Aspen cavity trees were larger than aspen random trees. Aspen cavity sites had more large snags and less ponderosa pine and were less steep than aspen random sites. Abert's squirrels possibly use cavities in large aspen trees because thick trunks and older trees might allow larger cavities to form, might provide greater thermal and wind protection, or both. The greater use of cavity nests by the Abert's squirrels in our study could be due to the higher frequency of cavity-forming aspens or harsher winter conditions in mixed-conifer forests of the Pinaleño Mountains than in ponderosa pine forests where Abert's squirrels typically occur or both.

Additional Information

CHARACTERISTICS OF ABERT'S SQUIRREL (SCIURUS ABERTI) CAVITY NESTS

Date of publication:

2006

Topics

Abert’s squirrels

cavity nests

aspen

ponderosa pine

mixed conifer forests

Pinaleño Mountains

Edelman, A. J. and J. L. Koprowski. 2006. Seasonal changes in home ranges of Abert's squirrels: Impact of mating season. Canadian Journal of Zoology 84: 404-411.

thackerk1 — Tue, 25 Jun 2019 01:06:09 +0000

Authors

A.J. Edelman

J.L. Koprowski

We compared home ranges of introduced Abert’s squirrels (Sciurus aberti Woodhouse, 1853) in mixed- conifer forests of Arizona during non-mating and mating seasons. Because Abert’s squirrels are reported to depend on ponderosa pine (Pinus ponderosa P. & C. Lawson) forests, the mixed-conifer forest in our study represented a novel habitat. Home-range size, home-range overlap with females, and movement distances increased for males from non-mating to mating seasons. Home-range size and overlap characteristics of females remained consistent between seasons, but movement distances were reduced during the mating season. Males probably increased home-range size, home-range overlap with females, and movement distances during the mating season to maximize contact with scarce females. Home-range size and overlap characteristics of female Abert’s squirrels likely remained stable between seasons because females do not search for mates. Restricted movements by females during the mating season may be due to changes in resource use in preparation for reproduction. Non-mating season home ranges in our study were smaller than home ranges observed in ponderosa pine forest. Abert’s squirrels in mixed-conifer forest may have small home ranges because resource quality is higher than in ponderosa pine forest or competition for space with co-occurring Mount Graham red squirrels (Tamiasciurus hudsonicus grahamensis (J.A. Allen, 1894)).

Additional Information

Seasonal changes in home ranges of Abert’s squirrels: impact of mating season

Date of publication:

2006

Topics

Abert’s squirrels

mixed conifer forests

home range

resource quality

sex differences

seasonal changes

mating season

Edelman, A. J., J. L. Koprowski, and S. R. Bertelsen. 2009. Potential for nest site competition between native and exotic tree squirrels. Journal of Mammalogy 90: 167-174.

thackerk1 — Tue, 25 Jun 2019 00:54:50 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Sadie R. Bertelsen

In communities where strong interspecific competition between native species is lacking, exotic and native species often exhibit intense resource competition resulting in decline of native populations. We examined the potential for interspecific competition for nest sites between co-occurring native Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis) and exotic Abert’s squirrels (Sciurus aberti) in the Pinaleño Mountains of Arizona. Comparison of nest use between red and Abert’s squirrels at different scales (nest, nest tree, and nest site) revealed contrasting results. Competition for nests and nest trees appears unlikely given the dissimilarity in use of nest types and tree characteristics. Abert’s squirrels predominately used dreys, whereas red squirrels mostly used cavity nests. Neither squirrel species occupied a nest used by the other species. Nest trees differed in size and species between squirrels for dreys, but not for cavities. Abert’s squirrel nest sites were found in a wider range of microhabitats including almost all microhabitats in which red squirrel nest sites were located. Although there was significant overlap, each species showed distinct trends in microhabitat. In general, red squirrel nest sites were characterized as more densely forested areas dominated by corkbark fir (Abies lasiocarpa var.arizonica), whereas Abert’s squirrel nest sites were more open and contained greater tree species diversity. Overlap in microhabitat characteristics increases the likelihood of interspecific competition and could increase the vulnerability of red squirrels to extinction.

Additional Information

Potential for Nest Site Competition between Native and Exotic Tree Squirrels

Date of publication:

2009

Topics

coexistence

introduced species

Mount Graham Red Squirrel

Abert’s squirrels

niche overlap

tassel-eared squirrel

pine squirrel

Doumas, S. L., J. L. Koprowski, and W. O. Noble. 2016. Landscape-level assessment of Abert's squirrel and red squirrel in mixed conifer forest. The Southwestern Naturalist 60:240-246.

thackerk1 — Tue, 25 Jun 2019 00:36:36 +0000

Authors

Sandra L. Doumas

John L. Koprowski

William O. Noble

We examined feeding sign of Abert’s squirrels (Sciurus aberti) and red squirrels (Tamiasciurus hudsonicus) each spring 2005–2009 in mixed conifer forests in northern Arizona, USA. We used high- resolution aerial photographs to assess vegetation characteristics where feeding sign surveys were conducted and analyzed the association of feeding sign frequency to vegetation characteristics to compare and contrast species habitat use. At the landscape level, we found considerable overlap in characteristics of forests used by the two species of native tree squirrels. Red squirrels used denser forests with fewer and smaller gaps than do Abert’s squirrels, and Abert’s squirrels used more ponderosa pine (Pinus ponderosa) than do red squirrels.

Additional Information

Landscape-level assessment of Abert's Squirrel and Red Squirrel in Mixed Conifer Forest

Date of publication:

2015

Topics

Abert’s squirrels

red squirrels

feeding signs

mixed conifer forests

habitat use