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Effects of Treating
Creosotebush With
Tebuthiuron on Rodents1
William G. Standley2and Norman S. Smith3
Herbicides are often used to control
shrubs such as mesquite (Prosopis juliflora) and creosotebush (Larrea
tridentafa), which have invaded millions of hectares of semidesert grasslands (Cox et al. 1982).The reduction
of shrub cover usually results in an
increase in forage production (Box
1964).
The herbicide 2,4-D has been used
for more than two decades and its
effects on rodent communities have
been extensively studied (Keith et al.
1959, Johnson and Hansen 1969,
Spencer and Barrett 1980).2,4-D has
varied effects on rodent communities, increasing the abundance of
some species, while decreasing the
abundance of others (Johnson and
Hansen 1969, Spencer and Barrett
1980).
Tebuthiuron is a thiadiazolyl-urea
herbicide (Walker et al. 1973)used to
control shrubs in the southwest (Herbe1 et al. 1985).No studies have been
conducted to determine effects of
tebuthiuron treatments on rodent
'Paper presented at symposium, Management of Amphibians, Reptiles, and
Small Mammals in North America. (Flagstaff, AZ,July 19-21, 1988.)
William G.Standley, formerly a graduate student, University of Arizona, Arizona
Cooperative Fish and Ulildlife Research
Unit, is currently Animal Ecologist, EG&G
Energy Measurements, Inc., c/o NPR- I , P.O.
Box 727, Tupman, CA, 93276.
3NormanS. Smith is Assisfant Leader, Arizona Cooperative Fish and Wildlife Research Unit, University of Arizona, Tucson, AZ
8572 1.
Abstract.-Three years after creosotebush (Lanea
fridenfafa)was treated with tebuthiuron, rodent
abundance was 7 1% higher on treated plots than
on control plots in southeastern Arizona. Arizona cotton rats (Sigmodon arizonae) and Western harvest
mice (Reithrodontomys megalotis)were more abundant while the abundance of Merriam's kangaroo
rats (Dipodomys meriami) was similar. We conclude
that tebuthiuron may be safely used to control creosotebush in semidesert grasslands unless the presence of rare or endangered species precludes any
alterations to the community.
communities. We studied grasslands
invaded by creosotebush in southeastern Arizona in order to determine changes that take place in a rodent community due to treatment
with tebuthiuron. We compared
vegetation and nocturnal rodents
present on control and treated plots.
Because tebuthiuron is nontoxic to
laboratory mice, rats, and rabbits
(Morton and Hoffman 1976) we assumed that any changes in the rodent
community would be in response to
changes in food supply, ground
cover, or both.
Methods
Two adjacent 150 x 600 m plots were
fenced from cattle, and one was aerially treated with tebuthiuron (1.0 kg/
ha) in May 1981 as part of an ongoing experiment on the USDA Forest
Service Santa Rita Experimental
Range, 45 km south of Tucson Ari-
zona. Vegetation on the plots is
dominated by creosotebush, with
sparse grasses such as threeawn
(Aristida sp.) and bush muhly
(Muhlenbergia porteri) (Martin and
Reynolds 1973).
We sampled vegetation and rodent communities in June 1984, three
years after herbicide treatment.
Vegetation was sampled using the
line intercept method (Canfield
1941). Six 30 m parallel lines were
systematically located on each plot.
Total intercepts of each species were
averaged and transformed into percent ground and canopy cover. Rodent communities were surveyed using the removal method. Sherman
live-traps (7.5 x 7.5 x 25 cm) were
used so that rodents could be used
for other studies. Three 8 by 8 grids
with traps spaced at 10 m intervals,
were placed on each plot. Grids were
placed as far from each other and
from plot boundaries as possible, resulting in a uniform distribution.
Traps, opened at sunset and closed at
sunrise, were baited with peanut
butter and oats. We prebaited traps
for one night then removed all rodents captured during the following
four nights. The total number of each
species captured on the three grids
on each plot were averaged.
treated grids accounted for most of
the difference in abundance. Cotton
rats and house mice (Mus rnusculus)
were captured only on the treated
grids, while Bailey's pocket mice
(Perognath us baileyi) and deer mice
(Peromyscus maniculatus) were caught
only on control grids.
Results
Discussion
Average grass cover on the tebuthiuron-treated plot was almost three
times that on the control plot (table
11, with threeawn contributing most
of the difference. Average shrub
cover on the treated plot was 98%
lower than on the control plot, with
creosotebush accounting for the biggest difference.
On tebuthiuron-treated grids we
captured 162 rodents of eight species,
and on control grids 95 rodents of
eight species (table 2). Higher numbers of Arizona cotton rats (Sigmodon
arizonae) and western harvest mice
(Reithrodontomys megalotis) on the
The dramatically greater grass cover
and lesser shrub cover on the treated
plot are consistent with results of
other experiments with tebuthiuron
(Herbel et al. 19851, as well as with
2,4-D (Spencer and Barrett 1980).
This difference in vegetative structure appears to account for most of
the differences in the rodent comrnunity. Studies of cotton rats and harvest mice have shown that both species are strongly associated with
dense stands of grass (Goertz 1964,
Ford 1977). The similarity in abundance of Merriam's kangaroo rats on
control and treated plots was unexpected since heteromyids are generally more abundant in areas with
sparse ground cover (Stamp and
Ohmart 1978).
We d o not present inferential statistics to test differences in ground
cover or rodent numbers because
both the line intercept transects and
trap grids were actually subsamples
rather than true replicates (Hurlbert
1984). We are convinced, however,
that differences between plots in
numbers of cotton rats and harvest
mice, are the result of habitat
changes following treatment with
tebuthiuron.
Because of the low numbers of
deer mice and Bailey's pocket mice
captured on the control plots, we do
not feel their absence on the treated
plots is significant. Because the responses were either neutral or positive, we feel that tebuthiuron can be
safely used by managers to control
shrubs in semidesert grasslands
without fear of endangering rodents
directly. However, the impact of
habitat changes on rare or endangered species should not be ignored.
Acknowledgments
This study was funded by the USDA
Arid Land Ecosystems Improvement
Unit. We thank J. Ard, J. Brown, B.
Kotler, and B. Zoellick for field assistance.
Literature Cited
Box, Thadis W. 1964. Changes in
wildlife habitat composition following brush control practices in
south Texas. Transactions of the
North American Wildlife Conference 29:432-438.
Canfield, R. H. 1941. Application of
the line interception method in
sampling range vegetation. Journal of Forestry 39:388-394.
Cox, Jerry R., Howard L. Morton,
Thomas N. Johnsen Jr., Gilbert L.
Jordan, S. Clark Martin, and Louis
C. Fierro. 1982. Vegetation restoration in the Chihuahuan and Sonoran deserts of North America.
United States Department of Agriculture, Agricultural Research
Service, Agricultural Reviews and
Manuals, Western Series Number
28, August 1982.
Ford, Steven D. 1977. Range, distribution and habitat of the western
harvest mouse, Reithrodontomys
megalotis, in Indiana. American
Midland Naturalist 98:422-432.
Goertz, John W. 1964. The influence
of habitat quality upon density of
cotton rat populations. Ecological
Monographs 34:359-381.
Herbel, Carlton H., Howard L. Morton, and Robert P. Gibbens. 1985.
Controlling shrubs in the arid
southwest with tebuthiuron. Journal of Range Management 38:391394.
Hurlbert, Stuart H. 1984. Pseudoreplication and the design of
ecological field experiments. Ecological Monographs 54:187-2ll.
Johnson, Donald R. and Richard M.
Hansen. 1969. Effects of range
treatment with 2,4-D on rodent
populations. Journal of Wildlife
Management 33:125-132.
Keith, James O., Richard M. Hansen,
and A. Lorin Ward. 1959. Effect of
2,4-D on abundance and food of
pocket gophers. Journal of Wildlife Management 23:137-145.
Martin, S. Clark, and Hudson G.
Reynolds. 1973. The Santa Rita
Experimental Range: Your facility
for research on semidesert ecosystems. Journal of the Arizona Academy of Science 8:56-67.
Morton, D. M., and D. G. Hoffman.
1976. Metabolism of new herbicide
tebuthiuron (1(5-(1,l-dimethyl1,3,4-thiadiazol-2-y1)-1,3-dimethylurea) in mouse, rat, rabbit, dog,
duck, and fish. Journal of Toxicology and Environmental Health
1:757-768.
Spencer, Stephen R. and Gary W.
Barrett. 1980. Meadow vole population response to vegetational
changes resulting from 2,4-D application. American Midland
Naturalist 103:32-46.
Stamp, Nancy E., and Robert D.
Ohmart. 1978. Resource utilization
by desert rodents in the lower
Sonoran desert. Ecology 59:700707.
Walker, J. C., M. L. Jones, and J. E.
Shaw. 1973. Total vegetation control with tebuthiuron-a new
broad spectrum herbicide. Proceedings of the North Central
Weed Control Conference 28:39.