Neotoma Fuscipes Research Articles

Wood Rats and Northern Spotted Owls in the Coastal Redwoods

Abstract Foresters often face the challenge of maintaining a flow of timber while managing for nontimber resources. In coastal redwood forests the need to protect dusky-footed wood rats--a potential prey for the spotted owl--while minimizing the damage caused by their feeding has created contradictory wildlife management objectives. Based on prior experience and preliminary field reconnaissance, however, it appears that stand prescriptions can be manipulated to control wood rat abundance and feeding behavior.

Forest Stand Characteristics and Reproduction of Northern Spotted Owls in Managed North-Coastal California Forests

We monitored reproductive success of northern spotted owls (Strix identalis caurina) at 51 sites on Simpson Timber Company's (STC) managed, young-growth forests in northwestern California from 1991 to 1995. We compared habitat characteristics between sites with high and low fecundity at 5 spatial scales (concentric circles of 7. 50, 114, 203, and 398 ha), using 2 stratifications of annual reproductive success (upper 50% vs. lower 50% and upper 25% vs. lower 75% of the proportion of years when ≥1 owlet fledged). Habitat features included number of residual trees per hectare and mean proportion of 6 categories of stand age and 4 categories of basal area. Using the 50th percentile categories, we found there were higher proportions of age class 21-40 years and basal area classes 23-45 and 46-69 m 2 /ha (P ≤ 0.05), but lower proportions of recent clearcuts (0-5 yr) and basal area >69 m 2 /ha (P ≤ 0.05) at sites with high reproductive success. Using the upper 25% and lower 75% categories, we found there were higher proportions of basal area class 23-45 m 2 /ha, lower proportions of 61-80-year-old stands and more residua trees per hectare at sites with high reproductive success (P ≤ 0.05). We also compared random sites to occupied sites via the above parameters, Spotted owl sites contained lower proportions of basal area class 69 m 2 /ha than did random sites (P < 0.05). There was less young forest (6-40 vr) and more forest of age class 41-60 vears at spotted owl than at random sites (P < 0.05). Low prey abundance around spotted owl nest sites, roost sites, or both mav explain why older stands with more basal area were found in higher proportions at sites with lower fecundity. Spotted owls that chose younger stands with smaller trees mav have benefited from higher woodrat (Neotoma fuscipes) availability in young stands. Managing habitat by retaining residual trees and limiting clearcutting to at least 1.1 km bevond lest sites may prove useful in increasing reproductive success of northern spotted owls.

A better tick-control trap: Modified bait tube controls disease-carrying ticks and fleas

In northwestern California, the dusky-footed wood rat is a primary reservoir of Lyme disease (LD) spirochetes and an important host of three tick species that collectively transmit the causative agents of LD, human granulocytic ehrlichiosis, Rocky Mountain spotted fever and tularemia. It also is infested by two flea species that can transmit the agent of plague. We refined a method of applying pesticides to the host using liquid permethrin-treated bait tubes, and found it to be highly effective for reducing populations of these ticks on wood rats in brushlands. Although permethrin products are not currently registered for this use, this approach offers a promising tool for controlling arthropod-borne diseases in the western United States.

Habitat Selection by Northern Spotted Owls: The Consequences of Prey Selection and Distribution

We tested three predictions of a hypothesis that states Northern Spotted Owls (Strix occidentalis caurina) select habitat according to the distribution of their primary prey. Our predictions were that Northern Spotted Owls should (1) select larger (> 100 g) species among the assemblage of available prey, (2) select habitats according to the distribution of large prey, and (3) the owl's reproductive success should be influenced by the availability of large prey. We also evaluated the potential energetic value of several prey species. We found that Northern Spotted Owls (n = 11 pairs and 1 single male) in northwestern California differentially selected the dusky-footed woodrat (Neotoma fuscipes), a moderately large sigmodontine rodent (x mass = 232 g). When foraging, owls selected late seral forest edge sites where dusky-footed woodrats were more abundant. Although the relationship between site selection, prey abundance, and the owl's breeding success was not statistically significant, the average abundance of dusky-footed woodrats at sites foraged by breeding owls (x = 11.4 woodrats 100-trap-nights -1 ) was greater than at sites foraged by nonbreeding owls (x = 4.7 woodrats 100-trap-nights -1 ). We estimated that a male Spotted Owl would require 150,015 to 336,232 kJ over a 153-day period while helping to produce one young, and concluded that the selection of woodrats provided a potential energetic benefit over the use of other prey. These findings provide a partial explanation for the owl's affinity for late seral forests.

Between-Habitat Movement of Dusky-Footed Woodrats and Vulnerability to Predation

Management of northern spotted owls (Strix occidentalis caurina) in northwestern California is aided by knowledge of its prey base, the dusky-footed woodrat (Neotoma fuscipes). From late April through September 1990, we radiotracked 25 dusky-footed woodrats representing both sexes and a cross section of age classes (ad, subad, and juv). Animals were captured in sapling/poletimber shrubfields resulting from past clearcut timber harvest. In northwestern California woodrats reach their highest densities in this seral stage. During evening radiotracking sessions, we detected intermittent, short distance movements of juvenile and subadult males and females, and adult females from shrubfields into adjacent old-growth forests occupied by spotted owls. None of the radiotagged woodrats permanently emigrated to older-aged forests during our study period. Between-year emigration from shrubfield to old forest, however, was documented for marked individuals. Our telemetry results indicate that woodrats are not averse to crossing sharp ecotonal boundaries from shrubfields into adjacent old forest, into canopy openings in these forests, or into natural openings within dense shrubfields. A substantial number of our radiotagged woodrats were killed by predators, with carcasses most often (5 of 9 depredated woodrats) found in adjacent old forest. These observations suggest that during these between-habitat forays, woodrats may be more vulnerable to avian and mammal predators. Therefore, to some degree, the existence of brushy shrubfields adjacent to older forest may increase the availability of woodrats to predators, such as spotted owls, that exploit prey from a variety of habitats but spend the majority of their time hunting in late seral stage forests.

Factors affecting the seasonal abundance of ground squirrel and wood rat fleas (Siphonaptera) in San Diego County, California.

Abiotic and biotic factors affecting the seasonal abundance of 3 species of sylvatic fleas on their hosts were examined at 7 sites in San Diego County, California. Indices for Oropsylla (Diamanus) montana (Baker) were usually highest on Spermophilus beecheyi nudipes (Huey) when < 18.4 degrees C (October-December), whereas those for Hoplopsyllus anomalus (Baker) were highest when > 18.4 degrees C (July-September). O. montana was affected most by ambient temperature (inversely for the coastal site [134 m] and directly for most mountain sites [> 1,183 m]). O. montana was affected most (directly) by relative humidity at the inland valley site, which concurs with this flea being most abundant in other areas during periods yielding higher relative humidties and moderate ambient temperatures. H. anomalus was influenced most (directly) by ambient temperature at lower sites (< 1,183 m) and by host activity at higher ones (> 1,456 m). Usually nonrandom distribution findings, when indices for each squirrel flea were higher on some hosts, indicate that flea numbers are correspondingly higher in some nests and burrows because of more favorable microconditions. Data also indicated that plague may persist at higher sites in southern California or in other areas where climatic conditions permit increased and prolonged interactions between more abundant O. montana and its host during spring through summer. Whereas, plague may have less chance of persisting at lower sites because these interactions are decreased and shortened during the warmer months. Squirrels may become infected with plague following hibernation and again when reoccupying colonial burrows. The flea Orchopeas sexdentatus was affected most (inversely) by relative humidity at a coastal site, with higher indices occurring on fewer Neotoma lepida Thomas and on more abundant Neotoma fuscipes macrotis Thomas during colder months. Such increased flea/Neotoma fuscipes Baird activity at lower sites may favor plague amplification during the winter which may involve ground squirrels and other rodents in the spring.

Evaluation of permethrin-impregnated cotton balls as potential nesting material to control ectoparasites of woodrats in California.

The dusky-footed woodrat, Neotoma fuscipes Baird is a natural reservoir of the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, in California. To investigate the potential of host-targeted insecticide to control the tick vectors of B. burgdorferi, permethrin-impregnated or untreated cotton balls were distributed in metal cylinders as potential nesting material adjacent to 95 woodrat houses in chaparral-covered rangeland. Laboratory experiments demonstrated that adult woodrats would enter the cylinders and construct nests from permethrin-treated or untreated cotton. The residual concentration of permethrin did not vary significantly during an 11-mo period and remained > 60% of the registered insecticidal formulation (7.5% [AI] by cotton weight). The abundance of 4 species of ticks (Ixodes neotomae Cooley; the western blacklegged tick I. pacificus Cooley & Kohls; I. woodi Bishopp; and the Pacific Coast tick, Dermacentor occidentalis Marx) infesting woodrats was similar in the treatment and control areas. Although > 90% of the cotton disappeared from the metal cylinders in both areas, examination of 8 active woodrat houses revealed that small amounts of cotton had been incorporated into the nest cups of only 25%. In contrast, the abundance of the flea Orchopeas sexdentatus (Baker) decreased significantly in the treatment area only. Spirochetes were not detected in 168 adult O. sexdentatus fleas that had fed on spirochetemic woodrats, which demonstrates that this flea is an inefficient host of B. burgdorferi. We conclude that the use of permethrin-impregnated cotton as potential nesting material is ineffective for controlling ticks associated with the dusky-footed woodrat in brushlands, but this methodology may be useful for reducing populations of sylvatic fleas.

Ixodes (Ixodes) jellisoni and I. (I.) neotomae (Acari: Ixodidae): Descriptions of the Immature Stages from California

Nymphal and larval stages of Ixodes (Ixodes) jellisoni Cooley & Kohls and I. (I.) neotomae Cooley are described for the first time. These 2 tick species occur only in the western United States, predominantly in California. The primary host for I. jellisoni is the California kangaroo rat, Dipodomys californicus (Merriam); that for I. neotomae is the dusky-footed woodrat, Neotoma fuscipes Baird. The etiologic agent of Lyme disease Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt & Brenner has recently been isolated from both tick species, and I. neotomae was proven a competent enzootic vector of the Lyme disease spirochete.

Reservoir Competence of Four Chaparral-Dwelling Rodents for Borrelia burgdorferi in California

Aspects of the reservoir competence of four rodents for the Lyme disease spirochete, Borrelia burgdorferi, were evaluated in California. Rodents were live-trapped and ear-punch biopsies were cultured during each season. A second set of biopsies was cultured from representative individuals after 2-3 weeks of captivity and the results of culturing biopsies taken on both dates were compared with the results of feeding Ixodes pacificus larvae on hosts xenodiagnostically. The prevalence of infections did not differ significantly between dusky-footed woodrats (Neotoma fuscipes) and California kangaroo rats (Dipodomys californicus) nor among seasons. Combined results of the three tests showed that 85.7% of dusky-footed woodrats (n = 21) and 78.6% of California kangaroo rats (n = 14) were infected with B. burgdorferi. In contrast, only 22.2% of brush mice (Peromyscus boylii) (n = 14) and 7.1% of pinyon mice (P. truei) (n = 9) were infected. The sensitivity of culturing ear-punch biopsies as an assay for borrelial infection was significantly greater when biopsies were taken after a short period of captivity (0.89) rather than on the day of capture (0.52). Tick xenodiagnosis, in which I. pacificus was used as the vector, revealed borrelial infections in 90.3% of infected rodents. Spirochetes were observed in 37.7% of 239, 45.2% of 155, 60.0% of 10, and 7.1% of 14 cultures of nymphal I. pacificus fed as larvae on naturally infected woodrats, kangaroo rats, brush mice, and a pinyon mouse, respectively. The mean prevalence of infection in xenodiagnostic ticks varied significantly among host species with a greater proportion of ticks infected while feeding on woodrats and kangaroo rats than on mice. This study reconfirms previous reports that implicated woodrats and kangaroo rats as reservoirs of B. burgdorferi in California.

Pollen Limitation and Population Growth in a Herbaceous Perennial Legume

woodrat, Neotoma cinerea. University of California Publications in Zoology 110:1-121. Gutierrez, R. J. 1985. An overview of recent research on the spotted owl. Pages 39-49 in R. J. Gutierrez and A. B. Carey, technical editors. Ecology and management of the spotted owl in the Pacific Northwest. U.S. Forest Service General Technical Report PNW-185. Menkens, G. E., Jr., and S. H. Anderson. 1988. Estimation of small-mammal population size. Ecology 69:1952-1959. Montgomery, W. I. 1987. The application of capture-markrecapture methods to the enumeration of small mammal populations. Symposia of the Zoological Society of London 58:25-57. Old-Growth Definition Task Group. 1986. Interim definitions for old-growth Douglas-fir and mixed-conifer forests in the Pacific Northwest and California. U.S. Forest Service Research Note PNW-447. Quinn, J. E, and A. E. Dunham. 1983. On hypothesis testing in ecology and evolution. American Naturalist 122:602617. Rosenberg, D.K., and R. G. Anthony. 1992. Characteristics of northern flying squirrel populations in young secondand old-growth forests in western Oregon. Canadian Journal of Zoology 70:161-166. Rosenberg, D. K., C. J. Zabel, B. R. Noon, and E. C. Meslow. 1994. Northern Spotted Owls: influence of prey base-a comment. Ecology 75: 1512-1515. Sakai, H. E, and B. R. Noon. 1993. Dusky-footed woodrat abundance in different-aged forests in northwestern California. Journal of Wildlife Management 57:373-382. Thomas, J. W., E. D. Forsman, J. B. Lint, E. C. Meslow, B. R. Noon, and J. Verner. 1990. A conservation strategy for the northern spotted owl. Report of the interagency committee to address the conservation strategy of the northern spotted owl. U.S. Forest Service, Portland, Oregon, USA. Volz, K. 1986. Habitat requirements of northern flying squirrels in west-central Oregon. Thesis. Washington State University, Pullman, Washington, USA. Witt, J. W. 1992. Home range and density estimates for the northern flying squirrel, Glaucomys sabrinus, in western Oregon. Journal of Mammalogy 73:921-929. Zar, J. H. 1984. Biostatistical analysis. Prentice Hall, Englewood Cliffs, New Jersey, USA.

Northern Spotted Owls: Influence of Prey Base‐‐A Comment

Conflicts between the needs of the Northern Spotted Owl (Strix occidentalis caurina) and the maintenance of a timber-based economy in the Pacific Northwest have motivated research on the habitat and area requirements of the owl. The Northern Spotted Owl has been studied extensively throughout its range and consistently has been found to select older forest stands for foraging, roosting, and nesting (reviewed in Thomas et al. [1990]). At least six hypotheses have been proposed to account for selection of older forests by Spotted Owls (Forsman et al. 1977, 1982, 1984, Carey et al. 1990, 1992, Rosenberg and Anthony 1992). Two of these relate to their prey. The prey hypotheses suggest that prey are more available to Spotted Owls by either or both of two mechanisms: (1) prey are simply more abundant in older forests (prey abundance hypothesis), and (2) prey are more efficiently hunted in older forests because of an increase in the ability of owls to forage through more open understory structure (prey availability hypothesis). Carey et al. (1992) recently reported on associations between Spotted Owls and their prey in Oregon and Washington. They concluded that the abundance of prey across a landscape determined the carrying capacity for Spotted Owls and that within-landscape features such as stand age and forest fragmentation affected the abundance and demographic characteristics of prey. Northern flying squirrels (Glaucomys sabrinus) and dusky-footed and bushy-tailed woodrats (Neotoma fuscipes and N. cinerea, respectively) are the most common prey of the Northern Spotted Owl throughout its range, constituting the majority of the biomass consumed by owls (Forsman et al. 1984). Carey et al. (1992) concluded that northern flying squirrels were more abundant in older forests, populations were more

NATURAL AND EXPERIMENTAL BORRELIA BURGDORFERI INFECTIONS IN WOODRATS AND DEER MICE FROM CALIFORNIA

Sequestration of spirochetes and concurrent histopathologic lesions were evaluated in tissues of Borrelia burgdorferi-infected dusky-footed woodrats (Neotoma fuscipes) and deer mice (Peromyscus maniculatus). Rodents were either wild-caught and naturally infected or were experimentally infected by tick bite, by intramuscular (i.m.) injection of cultured spirochetes, or by i.m. injection of tick suspensions. Samples of host tissues, including skin, blood, ear, brain, eye, heart, lung, liver, spleen, kidney, and urinary bladder, were removed from up to 21 woodrats and four deer mice and cultured in BSK II medium. Borreliae-positive cultures of ear punch biopsies were obtained from 10 of 11 woodrats and from all of four deer mice. Additionally, positive cultures were obtained from three of 36 skin biopsies of woodrats, and from one of 36 cultures of woodrat blood. In contrast, spirochetes were not observed in 505 cultures of internal organs or whole blood. Samples of tissues from seven naturally infected woodrats, four experimentally infected woodrats, and nine experimentally infected deer mice also were examined for histopathologic lesions. Nonsuppurative cellular infiltrates were recognized in samples from most tissue types from woodrats, but few lesions were observed in tissues from deer mice. Recognized lesions in woodrats that were consistent with infections of Lyme borreliosis in other species included synovitis, myositis, and myocarditis. Such lesions were more common in woodrats than in deer mice. Inflammatory lesions, especially synovitis, were more common in woodrats with long-term infections than in woodrats with relatively short-term infections. No clinical signs of disease were observed in either species of rodent.

Modifications of a cholinesterase method for determination of erythrocyte cholinesterase activity in wild mammals.

A method to determine erythrocyte cholinesterase (ChE) activity was modified for use in wild mammals. Erythrocyte ChE of California voles (Microtus californicus) was primarily acetylcholinesterase (AChE), which was similar to the brain and unlike plasma which was primarily butyrylcholinesterase (BChE). Triplicate erythrocyte AChE analyses from individual animals of several species of wild rodents revealed a mean coefficient of variation of 8.7% (SD = 4.3%). Erythrocyte ChE activity of several wild mammals of California revealed that mule deer (Odocoileus hemionus) had the highest erythrocyte AChE activity (1,514.5 mU/ml) and dusky-footed woodrats (Neotoma fuscipes) had the lowest activity (524.3 mU/ml). No ChE activity was found in erythrocytes of several species of birds and fish.

Home Range and Social Structure of the Dusky-Footed Woodrat (Neotoma fuscipes)

Home Range and Social Structure of the Dusky-Footed Woodrat (Neotoma fuscipes)

Genetic diversity among Borrelia burgdorferi isolates from wood rats and kangaroo rats in California.

Twenty-nine Borrelia burgdorferi isolates, obtained from dusky-footed wood rats (Neotoma fuscipes) and California kangaroo rats (Dipodomys californicus) in California, were analyzed genetically. Chromosomal DNA was examined by restriction endonuclease analysis (REA) and gene probe restriction fragment length polymorphism. Pulsed-field gel electrophoresis was used to analyze the plasmid profiles of the isolates. REA, the method with the greatest discrimination, disclosed 24 distinct restriction patterns among the 29 isolates. These restriction patterns were sorted into four restriction fragment length polymorphism groups on the basis of their gene hybridization patterns. Results of the REA and plasmid profile analysis supported this grouping. The degree of genetic diversity among Californian isolates demonstrated by our findings is greater than that previously reported among other groups of North American isolates and is similar or greater than the diversity reported among European isolates.

Dusky-Footed Woodrat Abundance in Different-Aged Forests in Northwestern California

Because dusky-footed woodrats (Neotoma fuscipes) are important prey species of northern spotted owls (Strix occidentalis caurina), we estimated their abundance in Douglas-fir (Pseudotsuga menziesii)/tanoak (Lithocarpus densiflora) forests of different ages in northwestern California. We surveyed and woodrats in 6-8 stands in each of 5 seral stages during the summers of 1988-90. We used belt transects to compute nest density, and livetrapped at nest sites to estimate woodrat numbers per nest. Combining these 2 sources of information provided an estimate of woodrat densities, which were highest in sapling/brushy poletimber stands, followed by seedling/shrub and large old-growth stands. Woodrats were not found in small sawtimber stands and rarely occurred in large sawtimber stands

First isolation of Borrelia burgdorferi in southern California.

The Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, was isolated from the blood of a dusky-footed wood rat, Neotoma fuscipes Baird, in the San Bernardino Mountains of southern California. Antigenic, protein, and molecular analyses demonstrated that the isolate varied slightly from most isolates of B. burgdorferi from northern California and was clearly distinct from other species of Borrelia that are endemic to the state. This is the first reported isolate of B. burgdorferi from southern California and demonstrates that the Lyme disease spirochete is enzootic in mountains near the major human population center of the state.

Wood Rats and Kangaroo Rats: Potential Reservoirs of the Lyme Disease Spirochete in California

The etiologic agent of Lyme disease, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, was isolated repeatedly from dusky-footed wood rats, Neotoma fuscipes Baird, and California kangaroo rats, Dipodomys californicus Merriam, in northern California. All animals were collected in a region endemic for Lyme disease but for which the natural reservoir of B. burgdorferi was unknown. Similar attempts to isolate spirochetes from lizards, other species of rodents, jack rabbits, and deer between 1987 and 1991 were unsuccessful. Spirochetes isolated from wood rats and kangaroo rats were antigenically similar to strains of B. burgdorferi that had been isolated previously from the western black-legged tick, Ixodes pacificus Cooley & Kohls, in California. Similar enzootic cycles involving wood rats or kangaroo rats should be sought in other regions of the United States where the reservoirs of this spirochete are unknown.

Element content in tissues of four rodent species sampled in the Geysers geothermal steamfield

Liver and kidney tissue samples from four rodent species collected in the Geysers geothermal steamfield of northern California were analyzed for content of 28 elements. Element concentrations in samples from the developed region of the Geysers were compared with samples from undeveloped reference regions to determine the influence of geothermal power development on element content in small mammal tissues. Eight elements (B, Ca, Cu, Mg, Mn, P, Sr, Ti) were enriched in samples from the Geysers, 12 (Ag, Al, Co, Cr, Fe, K, Mo, Na, Ni, Pb, Si, Zn) were decreased within the Geysers, Ba and Li were inconclusive, and six (As, Be, Cd, Hg, Sn, V) were below the minimum analytical limits. The longest-lived species ( Neotoma fuscipes) had the greatest occurrence of statistically significant differences in element content. Sites in grassland habitat produced more significant differences in element content than either chaparral or streamside habitats for samples from Peromyscus maniculatus. Peromyscus boylii and P. truei provided additional data, but no distinct advantages for element monitoring. The data indicate regional influences from geothermal power development on element levels in rodent tissues.

SEROLOGIC EVIDENCE OF YERSINIA PESTIS INFECTION IN SMALL MAMMALS AND BEARS FROM A TEMPERATE RAINFOREST OF NORTH COASTAL CALIFORNIA

From 1983 to 1985, 463 serum samples from 11 species of mammals in Redwood National Park (RNP) (California, USA) were evaluated for antibodies to Yersinia pestis by the passive hemagglutination method. Yersinia pestis antibodies occurred in serum samples from 25 (36%) of 69 black bears (Ursus americanus), one (50%) of two raccoons (Procyon lotor), five (3%) of 170 dusky-footed woodrats (Neotoma fuscipes), and one (less than 1%) of 118 deer mice (Peromyscus maniculatus). Two hundred seventy-three flea pools, consisting of 14 species of fleas, were collected from small mammals and woodrat nest cups. Viable Y. pestis were not isolated from any of the flea pools. Significant between-year variations in the frequencies of seropositive bear or small mammal sera were not observed. A significantly higher frequency of plague antibodies was observed in bear sera taken during September collections. Frequencies of seropositive bear sera did not vary significantly by sex or age group of bears. Significant differences were not observed in the frequencies of seropositive small mammals by forest habitat type in which they were captured. This is the first report of Y. pestis infection in Redwood National Park, and the first detailed report of Y. pestis activity in a temperate rainforest.