1. ECORAT PROJECT
Development of Ecologically Based Rodent Management for SADC Region
Abstract
The aim of the Ecorat project is to develop ecologically based rodent
management in southern Africa by investigating the rodent problems affecting
small-scale farmers in the region. Ecologically based rodent management is
increasingly seen as more sustainable, both economically and environmentally,
than the traditional use of poisons. It is therefore important to raise awareness
and gather accurate information about the health risks posed by and the extent of
the crop damage caused by rodents in Namibia
The Ecorat project is co-ordinated by scientists at the Natural Resources Institute
of the University of Greenwich in the UK, and involves organisations in
Swaziland, Tanzania, South Africa and Namibia. The international Ecorat project
started with an inception workshop at the University of Greenwich in January
2007, which was attended by scientists from the four countries.
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2. 1. Introduction
As part of training of my studies at Polytechnic of Namibia, I was recruited by
ECORAT project through the partner National Museum of Namibia (NMN) to
have hands on experience.. The museum is situated on three premises with
administration, curation, research, education and the library held at Museum
ACRE, the display centre at Owela Museum and Alte Feste. The Museum ACRE
is located in 59 Robert Mugabe Avenue, in a historical building that served as the
first school in Windhoek and was built in 1907/08 respectively.
The ECORAT project started with an inception workshop at the University of
Greenwich in January 2007. The ECORAT project is investigating the rodent-pest
problems affecting small-scale farmers in southern Africa. This international
agricultural research project started working in Namibia to develop Ecologically-
Based Rodent Management for the Southern African Region. The ECORAT
project is coordinated by scientists at the Natural Resources Institute (NRI) of the
University of Greenwich in the UK and involves organisations from Swaziland,
Tanzania, South Africa and Namibia. The aim is to strengthen the generation of
appropriate, cost-effective and sustainable rodent pest management technologies
and strategies for small-scale farming in the SADC region. In Namibia field work
for monitoring rodents is taking place at Mukwe constituency in Kavango
region.
I have been stationed at Frans Dimbare Rural Youth Centre (picture 1) for five
months in order to undertake field work and one month at Museum ACRE for
data analyses and reports writing. Frans Dimbare Rural Youth Development and
Environmental Centre is located 195 km east of Rundu between Andara and
Divundu on the banks of the Kavango River. The roughly 100 hector plot is
dominated by the river and its abundant indigenous forest. The aim of the centre
is to empower unemployed rural youth of this country but more specifically, by
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3. assisting young people in Kavango region in building health awareness,
developing educational and vocational skills as well as training courses such as
computer repairs, tailoring and agriculture (picture 1, 2&3).
Pic. 1 FDYC administration Pic. 2 Computer lecturing session Pic. 3 FDYC vegetable garden
2. Objectives
2.1. Employer’s Objective
The National Museum’s main objective is to preserve, comprehend and
elucidate the material heritage of our country for the present and future
generation.
2.2. ECORAT Research Project’s Objectives
a. To reduce high level of rural poverty in Southern African countries by
making agriculture more competitive, and to raise poor farmers’ income by
cost beneficially increasing crop yields, reducing storage loss and
preventing the transmission of diseases to people and livestock caused by
rodents.
b. To offset the high rate of natural resource degradation particularly small
mammal biodiversity through improving the management and invasion of
commensal rodents and increasing knowledge about rodent-human
interactions and agricultural expansion
c. To develop effective rural policy options with institutions and farmer
groups to support rodent pest management actions. Policies will be
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4. developed and introduced to ensure the right tools and knowledge is made
available to rural farming communities and to inform national regulations
regarding rodenticides, research provision and extension staff training
2.3. Personal Objectives
To carry out essential ecological research that is required to develop
sustainable community-managed rodent pest control strategies
To gain self-reliance in working with communities and research institutes
To gain scientific research knowledge and skills in Natural Resource
Management field in general and in particular to increase my knowledge and
understanding for rodent-pest management.
3. Project Activities
3.1. Rodent Ecology
3.1.1. Habitat utilization and inter-specific interactions
In general, studies on rodent habitat utilisation and inter-specific interactions
were carried out by live and kill trapping of rodents at two villages, Kake and
Diyogha. Trapping was done at different habitats ranging from crop fields,
inside houses, in peridomestic areas and around key sites in rural communities
(community centre and hospital). The habitats mentioned above are under the
removal sites, where animals are being removed. A total of 387 traps were used
in five trapping sites monthly. The traps used were snap (kill) traps (picture 5)
and Sherman live traps (picture 4). A mixture of peanut butter and oats (picture
6) were used as bait in traps. At all sites, the traps were set before sunset and
early morning for three consecutive nights in each month of trapping session.
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5. Pic 4. Baiting in sheman live traps Pic 5. Snap kill trap Pic 6. Bait peanutbutter&oats
3.1.2. Capture methods
3.1.2. (a) Trapping in the crop fields (millet field)
A study site was established in a crop field (millet field) at Kake village, arranged
in grid format (picture 7) measuring 70m× 70m with 49 trapping stations
arranged at an interval of 10m between traps (picture 8). A total of three grids
were used for three consecutive nights in each trapping session. Alternation of 10
snap traps and 39 Sherman live traps were used in each grid. Animals caught in
Sherman live traps were sacrificed and sampled for blood, tissues, endoparasites
and ectoparasites. For both animals caught in Sherman and snap traps, breeding
conditions (scrotal vs non-scrotal, perforated vs closed vagina, lactating vs non-
lactating), internal breeding conditions (size of testes, implantation of embryos,
no embryos, size, scars) were identified. Taxonomic data were recorded the body
weight, head and body length,) of all captured specimens. Data will be analyzed
for temporal and spatial changes at Sokoine University of agriculture (SUA),
Tanzania.
Pic 7. Setting up 70x70m grid in a crop filed Pic 8. Sherman live trap at a grid station
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6. 3.1.2. (b) Trapping in houses and Peridomestics areas
The locations of traps in houses and peridomestic areas were partly directed by
the household and variations in building structure and size. Five traps were set
in each peridomestic area and household. A total of 30 household were sampled
in 2 villages Kake and Diyogha (15 per village). The specimens collected will be
used for the diversity of the commensal rodent communities in domestic areas in
rural settings, rodent abundance in rural houses and status of each species,
parasites load, blood and tissues taken for pathogen determination and for
potential disease transmission to humans( test for 4 diseases-plague,
Leptospirosis, toxoplasmosis, lassa fever and borelia). These studies will enable
the establishment of the eco-epidemiology of these diseases in the study areas.
Data are being sent to SUA, Tanzania for analyses.
3.1.2. (c) Trapping at Community centers
Thirty traps were set in each center, Frans Dimbare Youth Center and Andara
Hospital. 25 Live traps were set in each center to allow the collection of blood,
tissues and ectoparasites. This will allow the data analysers in Tanzania to test a
hypothesis whether the risk of contracting rodent borne diseases is directly
related to the magnitude occurrence of commensal rodents and the remaining 5
traps are kill traps for removal and identification of abundance species at the
community centers.
3.1.3. Procedures of processing trapped animals
Live trapped animals from the removal sites are being anaesthetised using
chemicals called chloroform. A layer of cotton wool is soaked in chloroform and
dropped in a zip-lock with the animal and left for few minutes until the animal is
unconscious (picture 9).
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7. Pic 9. Staff in the project anaesthetising a specimen
Soon after anaesthetising the animal, blood sample is taken from the heart or
retro-orbital sinus using syringe and needle. The collected blood sample is kept
in labelled eppedorf tubes and stored at the temperature of -4°C. The blood taken
will be tested for possible zoonotic diseases.
Pic 10 taking blood sample from specimen
Then specimens are being identified to genus or if possible to species level using
a rodent’s dichotomous keys (De Graaff 1981; Stuart 1988). From there, sex and
the reproductive status is being examined (picture 11, 12 by Krebs, C.J. 1999). In
males, testes are being examined whether Abdominal or Scrotal (hanging), if
scrotal, it is an indication of sexually active (breeding). In females, the following
are being recorded; vagina perforated or closed, lactating or not lactating
(mammae large/small) and pregnant or not pregnant.
Pic 11. Comparison between juvenile (abdominal testes; left) Pic 12. Comparison between juvenile (closed or imperforate
(scrotal testes; right) males. Vagina; left) and adult (open or perforate vagina; right) females
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8. Immediately after that, the animals are brushed to remove ectoparasites. The
collected ectoparasites are preserved in labelled eppendorf tube with 70% alcohol
before being sent for identifications at the National Museum of Namibia.
Pic 13 collecting ectoparasites
After removing ectoparasites, the followings measurements are being taken;
body weight (g) using a Pesola spring balance as shown in picture 14, and left
hind-foot, ear, tail and head-body (mm) using a normal standard ruler.
Pic 14. Body weighing
From there the specimens are being dissected to take out tissue samples, gut
contents and for the internal reproductive status examinations (picture 15). Fresh
pairs of scissors and forceps dipped in 96% alcohol are being used to open the
abdominal and thoracic cavity. Livers and kidneys are the tissue samples that are
being taken, preserve them in a labeled vial with 96% ethanol and store them at
the temperature of -4°C. These samples are being sent to the Durban Natural
Science Museum for DNA analysis. Gut contents (small &large intestines,
stomach and caecum) are being removed, preserved in a labeled vial with 2%
formalin and these are being sent to the University of Swaziland for
endoparasites examinations.
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9. Pic 15 female adult specimen in second
trimester of pregnancy with seven healthy
embryos
Then a tag with a unique collection number is attached to each specimen (picture 16).
This number is on all data-forms and vials and used as a common reference for any given
individual.Then the dissection cut is closed with a needle and a thread after tissue
sampling (picture17). Carcasses are thrown in formalin solution, left for three days and
transfer them in 70% alcohol before sending them to the Durban Natural Science
Museum for further identification.
Pic 16 closing dissection cut Pic 17 tagging specimen
3.1.4. Population dynamics
Population dynamics studies are being carried out in two fallow lands, by using
a Capture Mark Recapture (CMR) method. These sites are at 1 km apart at Kake
village. The traps are being set in a grid format in a plot measuring 70m× 70m
with 49 marked trapping stations arranged at an interval of 10m between
stations. Traps are being set three consecutive nights in every month at each plot.
Data are being collected from these plots to establish population density changes,
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10. seasonality of population patterns (breeding and reproduction, survival and
mobilization). Sherman live traps are being used, on each captured animal, the
weight and the external breeding conditions (scrotal vs non-scrotal, perforated vs
closed vagina, lactating vs non- lactating) are being noted. If it is a new capture,
an animal is given a unique code (picture 19) using a toe clipping method
(picture 18), and then released at a specific station where it was trapped (picture
20). Rainfall data, temperature and relative humidity are always being recorded
during processing. The data collected will be used for demographic or
population analyses. Preliminary analyses show that although several small
mammal genuses are represented at the study sites, by far the greater part of the
animals is Mastomys sp a small amount of saccotomys sp is also found in two of
the study sites, Generally speaking the population dynamic patterns and
reproduction of both Mastomys sp. and saccotomys sp. show seasonality, and may
relate to the rainfall pattern, although more data are needed for proper
interpretation.
3 6
2 4 5 7
1 8
30 40 70 80
50 60 90
20
10 100
Pic 18 code method Pic 19 toe clipping Pic 20 specimen released after mark
4. Rodent-Human Interactions
The main objective of this study is to assess habitat utilization and overlapping
resources uses between rodents and human. Techniques such as radio telemetry
and spooling can be used to study the movements of animals. For this study,
radio telemetry was used. Telemetry involves attaching small radio collars to
animals and monitoring their movements with a handheld receiver. This
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11. research will help establish the degree to which different rodent species come to
contact with areas of human settlement and the potential interaction between
different rodent species utilizing the same habitat. One species (Mastomys
natalensis) was selected for the radio telemetry study. Three sessions, pre-harvest
(food abundantly available in the field), post-harvest (food available in grain
storage), and pre-planting (little food available in the field), are to be conducted
for this study. The first session was conducted during my In-service Training
period (picture 21-23).
Six individuals were captured in different habitats, collared and released at the
capture points. Radio tracking started the following day after the release and the
animals were tracked for five nights in different time intervals (17h00-21h00,
21h00-01h00 and 01h00-05h00). Radio-tracking involved taking fixes at 10 minute
interval (when the animal is not moving) and 2 minutes (when the animal is
moving). At each fix, GPS, time and compass reading are recorded and the
habitat noted. The receiver was used to pick up the signal being emitted by the
transmitters attached on the animals tracked.
Pic 21 ready to radio track Pic 22 finding day roost Pic 23 radio-tracking in the night
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12. 5. Administration
Administration work is also part of the duties in the ECORAT research project. I
was involved in acquiring quotations from different companies. Once all
quotations are received, prices are compared and one company is recommended,
the selected company receives an order form in return for goods and an invoice
is then payout. As a research trainee, I was entering the data in the excel sheet
and writing of monthly reports on how we are using the fuel, kilometers
travelled and meetings held with the communities.
As a trainee, I designed a leaflet about ECORAT research project, how it was
initiated, where and when, aims, the activities of the project, the partners
involved in the project and the funding source.
6. Community meetings and presentations
In January 2008, Capture-Mark and Recapture (CMR) plot 1 was cleared for
ploughing by the owner of the field. The plot was identified as a fallow land
before the beginning of the Ecorat research and a permission to use the plot for
CMR study was granted to Ecorat by one of the member who claimed to be the
owner. Ecorat staffs discovered the situation and called a meeting which was
held at Diyogha village (picture 24). The meeting involved two headmans (from
Kake and Diyogha), the former and current owner of the field and other
additional members of the community. At the end of the meeting an agreement
was reached between the real owner and Ecorat that the owner should be
compensated.
Picture 24 shows the community meeting
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13. On the 20th March 2008, there was a workshop for tour guide by Wildness Safari,
whereby, we were invited to give a presentation about ECORAT Research
Project. I presented my research about Rodent Damage Assessment in millet
fields, the purpose and the expected outcomes. Ecorat staffs explained how the
project started, aim of the project, activities of the project and the donors.
7. Reflection on the duty station and ECORAT staff teamwork
I honestly liked the teamwork of the project coordinator and the two ECORAT
research technicians I worked with during the period of my training. I found
them to be hard working, inventive and people of awe-inspiring working with
and I learned a lot from them. Though I was a research trainee, staff members at
Frans Dimbare Youth Centre regarded me as a well disciplined person, a person
who is willing to learn, mental alert and likes bringing up creative things which
was very useful to the youth, community and staff members. I learned more on
writing scientific reports, research project, gained scientific experience, and
radio-tracking which I thought I will never know in my life, processing small
mammals and toe clipping of live animals. The research exposed me to work
with many communities learning the culture and religious of those communities
and it was so beautiful to adapt with them. Generally, I would say the staff
members of my two duty stations Frans Dimbare youth centre and National
museum have very good personalities, a sense for cooperation and devotion to
their work.
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14. 8. Conclusions
In my personal point of view, Frans Dimbare Youth centre is not a very perfect
duty station for research purposes because it lacks some standard for a research
station, not having a library, internet and communication is not that accessible.
However, it was fine with ECORAT research project because they chose local
village near the center for the research. The project provided a car, tents, lights
and a computer for storing the data but it did not provide internet. During my
training I mainly became involved with the research work of trapping, radio-
tracking, capture and mark study, data entry, assessing damage in millet fields
and writing monthly reports. Within six months, I could conclude that ECORAT
project is a scientific project which is researching on pest management control in
agriculture. Working at the National Museum with ECORAT project, enhanced
my understanding of damage caused by rodents and possible diseases that can
be passed to humans by the rodents. During the six months period I gained
experience in trapping rodents, collecting ectoparasite, preservation of carcasses,
processing of small mammals, tissue sampling, research designing, driving,
working with communities and other technical experience such as chemical
solution preparation and taxonomic identification of rodent species. Generally,
the two duty stations have very good working environment and the two research
technicians work very hard to attain the mission statement of the ECORAT
research project. I enjoyed every single hour of my work during my training at
the two duty stations and I have no doubt regarding my further research and
work as a permanent agricultural research technician.
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15. 9. Reference:
1. De Graaf, G. 1981. The rodents of southern Africa. Pretoria: Butterworth.
2. Krebs, C.T. 1999. Ecological Methodology. Menlo Park, California, Benjamin
Cummins, 620p
3. Stuart, C.T. & Stuart M.D. 1988. Field guide to the mammals of Southern
Africa. Cape Town: Struik Publisher
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16. PROJECT REPORT
PREHARVEST RODENT DAMAGE ASSESSMENT ON MILLET
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17. Abstract
In this study the aimed was to assess preharvest rodent damage on millet. The
stratified random sampling technique was used to provide data to achieve
precision and accuracy in estimations of rodent damage in millet fields at the
planting and preharvest stage. The rodent damage distribution was divided in
strata in 2 millet fields, each 0.5 ha in size, Kake village in Mukwe constituency,
Kavango region, was established at the 10 days after planting. These data were
used to the estimate the distribution of damage and estimation in millet fields,
using quadrates that would provide precision and accuracy. Wilcoxon rank sum
test was used to find the significant difference for damage distribution and
estimation. The results of this study show that the distribution of damage is a
high at the centre than edges of millet fields. The heterogeneous distribution of
damage in plots caused variations in the accuracy of the estimates between plots,
but trapping rats in plot B produced estimates with average percentage damage
values of 8.6% than untreated plot B values of 11.03%. Wilcoxon rank sum test
table and critical value table was provided to allow a hypothesis to be accepted
based on the significant difference and on the distribution of damage and
estimation as a function of required precision using the stratified random
sampling technique in millet fields.
Key words: critical value, distribution, estimation, hypothesis, preharvest,
quadrates, rodents, strata, stratified random sampling technique, Wilcoxon rank
sum test.
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18. 1. Introduction
Rodent damage to crops is a serious obstacle in agriculture (Fiedler, 1988;
Singleton et al. 1999). Preharvest damage to cereal crops is a chronic problem in
the world. Losses are reported to be substantial (Ahmed et al., 1986; Poche et al.,
1982; Posamentier & Alam 1980; Posamentier 1981,). Farmers in many parts of
the world, particularly those in developing countries, tend to view economic
losses due to rats and mice as unavoidable (Posamentier 1997; Singleton et al.
1999). In fact, the impact of rodents has been greatly underestimated and
generally ignored in the general scientific literature, with a small number of
exceptions (Elton 1942; Singleton et al. 1999).
The principal pest rodents in Namibia millet fields are stem cutting (farmers’
observation). In addition to what it consumes during the growing season , the
rodent dig freshly sown seeds out of the ground, leaving a funnel shaped holes
(picture1), and may sometimes leave husk of the seeds nearby burrows systems
(picture 2). Burrows are commonly in bunds or bushes demarcating the
individual fields.
Pic 1. Freshly sown seeds dug by rodents Pic 2. Shows refuge or burrow for rodents in a field
Rodent damage effects in agriculture are complex because almost all crops are
the target of rodent attack (Fiedler, 1988; Singleton, 1999). Rodents are
responsible for considerable damage to food and play an important role as
reservoirs and carriers of zoonotic diseases. Survey reports in Tanzania, from
empirical data have shown that on the average, rodents caused about 15% loss of
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19. maize crop annually (Makundi et al., 1991). In Indonesia, rodents are the most
important pre-harvest pests in economic terms, causing on average at least 15%
annual losses of rice (Geddes 1992).
However, many farmers in Namibia complain of substantial loss of maize and
millet in their fields particularly small-scale farmers. The present study provides
the first information on the damage distribution, the magnitude and extent of
preharvest losses in Namibia. Millet production in Namibia is increasingly
popular among small-scale farmers. Millet is well adapted Namibian staple
drought resistance crop, as Namibia is a semi-desert country. Maize is more
difficult to cultivate for small- scale farmers because it requires frequent
irrigation or rainfall, most of which is done by hand and on commercial. Millet
requires little cultivation and watering after broadcasted.
In this study, I investigated the rodent damage distribution, damage estimation
and effect of stem cutting on preharvest yield on millet using stratified random
sampling method. The method was also used to test the following hypothesises,
that rat damage is highest in the middle of the crop field and lowest around the
edges and also that trapping rats reduce damage.
2. Project Objectives
To assess the distribution of rodent damage in the millet fields.
To estimate preharvest damage caused by rodent pests on millet
To determine the effects of stem cutting on yield.
To compare rodent damage in fields surrounded by fallowland and bushes
3. Personal Objective
To understand the relationship between the growth stages and intensity of
crop damage
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20. To gain self-reliance in working with communities and research institutes
To gain scientific research experience in Natural Resource Management.
To generate appropriate research knowledge to improve rodent management
practices in agriculture
4. Hypothesis
Rodent damage is highest at the center of millet fields than around the
edges
H 0 : The amount of damage in the centre is the same as that at the ages.
H1 : There is more damage in the centre than at the edges.
Trapping rats can reduce damage on millet
H 0 : The damage in the treated plot B is the same as that in untreated plot A.
H1 : The damage is less in the treated plot B than untreated A.
5. Materials and Methods
5.1. Study plots and area
The study was conducted at Kake village near Divundu. Divundu is situated
about 200km east of Rundu in Mukwe constituency of the Kavango region
(Picture 3-4). The main ethnic group in the area is the Hambukushu, one of the
five kingdoms in the Kavango region. As most parts of Namibia, farming in this
region is all subsistence, with farmers owning an average of 1 to 5 ha of crop
fields per household. Two millet fields sites were selected both at Kake village,
millet field site (Plot A), was part of monoculture millet field surrounded by
fallow land (picture 3) and cultivated fields. Plot A was located at 18° 05’ 25.3”S,
21°30’59.3”E at an altitude of 1011m. Predominantly soil type is sandy clay loam
soil. The other millet field site (plot B) was located in mosaic landscape of millet
field surrounded by bushes (picture 4), sited at 18° 05’ 20.1”S, 21° 30’ 28.8”E at an
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21. altitude of 1019m. Predominantly soil type is sandy loam soil. The study was
conducted during the cropping season which is also the main millet/mahangu
growing season (January-April 2008). The study size plots of 70m x 70 each were
located in each two field sites. The plots were at least 600m apart, so that none of
the two millet fields influence the rodent population of the other field. The seed
were sown in late January, and assessed early second week of February until the
late second week of April in both fields. The experiment was carried out every
second week for a total of four months in each plot. The millet seeds were
broadcasted and manual weeding was carried out once in both fields.
Pic 3 Plot A surrounded by fallow land Pic 4 Plot B surrounded by bushes
5.2. Sampling procedures
Two millet fields were selected at Kake village concerning rodent pest problems.
The information was obtained through discussion with farmers at Kake village,
on areas which were perceived to be at low and high risk of rodent damage. In
millet crop field, the distribution of damage within each field was highly
variable. A stratified sampling technique (Mulungu, 2003) was used in both
fields of 70m x 70m each, where rodent damage was heterogeneous (i.e. not
randomly distributed but higher in some zones than in others). The sampling
procedure for stratified random sampling begun with the definition of the
strata—the damage levels within the millet fields. Estimates were made
separately in each of these zones and were combined taking the relative size of
each strata into account. One goal of stratification was to create sub-universes
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22. that are uniform internally, i.e. to minimize variation within strata and
maximimize variation among strata. Visual estimation was rapid and is the
method most widely used to obtain distribution of rodent damage to agricultural
crops (Stevenson and Virgo 1971; DeHaven 1974a; Dolbeer 1975; DeHaven and
Hothem 1979). This was achieved by assigning a damage ranking strata within
the each field.
During the study, within each stratum a quadrate of 1m2 was randomly selected
in areas of similar damage intensity. A total of six quadrates were used in each
plot of 70m x 70m. The number of quadrate per a given damage level (stratum)
was depending to the proportion of the whole crop field. The proportion of each
stratum in each crop field was determined by visual estimates of how much the
stratum occupy per field. In plot A, stratum of low occupied 60% and medium
40% and four quadrates were set up in low stratum and two quadrates in
medium. In plot B, stratum of low occupied 70%, medium 30% and three
quadrates were set in stratum of low, three quadrates in stratum of medium. The
quadrat setups were depending on the variability of rodent damage levels in the
field. The more quadrats number per field the more precision. Nevertheless, it
has been reported that at least five quadrats within at field of 70m x 70m are
enough as a sample size. In both study fields, six quadrats were set up within at
field of 70x 70m. The quadrats within each study plot were plotted on the map to
visually verify where in each field distribution would have occurred (picture 4-
5).
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23. L M M
M
M L
M M
L
L
L L
Pic 5 Plot A study layout 70 x 70m Pic 6 Plot B study layout 70m x 70 m
Zigzag line is the stratum boundary, L =Low M=medium =quadrat
5. 3. Distribution of damage
Assessing the damage caused by rodent on millets fields was an important tool
to quantify damage estimation and distribution of damage. Assessment of rat
damage and distribution was performed in two millet fields of 70m x 70m each
with varying degree of rat damage. Both millet fields were superficially surveyed
by visualizing stem distribution damage caused by rodents, at a seedling stage,
10 days after planting. The distribution of damage was identified by walking
across each field and assessed the rodent stem damage. The stem is defined as
that portion of the plant that gives rise to a panicle (i.e. seed head). Cut stems
were widely distributed in both millet fields (Plot A and Plot B) as were
undetectable in low damage stratum during cursory examinations. Moderate
damage was visually seen as patches of the heavily damaged plants surrounded
by areas of relatively light damage (Buckle, A.P. 1994). Heavy damaged stratum
in both fields was not observed; only two strata were assessed (low and medium
damage, picture 7-8). In each field, one quadrate was set in the center and one at
the edge and total of four quadrates were examined. The total of stems and the
number of rat damaged stems were enumerated within each quadrate and the
percentage damage was determined for center and edge.
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24. Pic 7 shows medium damaged quadrat Pic 8 shows low damage quadrat
To give the percentage damage, the two center quadrates in both fields were
summed up and ranked; also the same was applied to the quadrates at the edges
of the two fields. Percentage of the stem damage at the center and edge was
compared. Near the edge of the field (i.e. around the perimeter of the field) of
each field were not sampled because of frequent goat damage and prevent
sampling of abnormal damage in relation to barriers. The Wilcoxon rank sum
test, which is a non-parametric technique, was used to compare the distributions
and testing hypotheses concerning the damage distribution in fields. I chose this
technique because I was not sure whether the data was normally distributed or
not.
5.4. Rodent crop damage estimation
Crop damage in plot A and plot B was assessed from the first week of February
2008 to second last week of April 2008, counting the number of freshly cut stems
and uncut stems every second week in each quadrat set in the strata (fig 8). Six
quadrats were in each plot of 70m x 70m and divided according to the
proportion of the stratum size. The information was recorded on a standard
damage assessment data sheet I designed (see appendix 1). Estimates were
calculated by counting the number of damaged and undamaged samples within
a crop. Although counting has been used to estimate total damage, a common
use of this method is to calibrate visual estimation methods (Stevenson and
Virgo 1971; DeHaven and Hothem 1979; Somers and Morris 2002).
The number of stems cut for the desire intensity of damage was computed as:
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25. D = n/N x 100
Where, D = % number of stems cut
n = number of stems cut
N = total numbers of stems
Estimated mean percentage proportion damaged averaged over all strata
(pˆST):= sum of stratum size × average proportion
The proportions of damaged stems to undamaged stems in a sample of
individual plants were used as an estimate of the damage to millet. After the
estimation, the mean percentage stem damage in millet field sites of untreated
and treated compared.
Pic 9 shows cut stems by rodents in a quadrat Pic 10 counting cut and uncut stems in qudrat
25

26. 6. Results
6.1. The distribution of rodent damage
Wilcoxon rank sum test (table 1)
Table 1 shows percentage stem damaged in fields by rodents at the center and edge
Center Edge %
%damged Rank damged Rank
21 22 12 17
18 20 8 11
16 19 6 8
11 15 0 3.5
11 15 0 3.5
0 3.5 0 3.5
24 24 13 18
27 25 4 7
20 21 0 3.5
10 13 9 12
0 3.5 7 9.5
11 15 7 9.5
TC 196 TE 106
14.1% 5.5%
average average
stem stem
damage damage
Damgd= damaged, TC = total ranks of center, TE = total ranks of edge
Significance level, α =0.05
Number of observation per sample= 12
Smallest sum of ranks= 106
Largest sum of ranks= 196
Critical region (5%) is "D ≥1.645"
Critical region (1%) is "D ≥2.33"
Calculated statistic, D = 2.568
The calculated statistic, D, lie within the critical region and therefore the test is
statistically significant at the 5% level so null hypothesis is rejected. The
conclusion is that there is more damage at the center than the edges. Results
indicate that the distribution of damage appeared to be relatively high at the
center than the edge (table 1), regardless whether it was in monoculture or
mosaic field. The same conclusion is also made at the 1% level of significance. It
accepted the hypothesis that states Rodent damage is high at the center than
edge of millet fields. The average percentage stem damage values of 5.5% for
edge and 14.1% for center. The results show a great average difference of 8.6 %
26

27. stem damage between center and edge. The occurrence of distribution stem
damaged for two fields sampled from seedling to preharvest revealed that the
14. 1% stem damaged at the center of fields predominated 5.5% stem damaged at
the edge. In general, the distribution of damage of damage at the fields’ levels
indicates that rodents are more active at the center and less at the edge.
6.2. Estimation of rodent damage on millet
Table 2
Number of the sampled stems damaged by rodents
Plot A
Quadrat damgd Total counted Stratum %stem %damage
no stems stems size damgd proportion stratum
QA1 14 78 0.6 18 10.8 Low
QA2 30 97 0.4 31 12.4 Medium
QB1 18 47 0.4 38 15.2 Medium
QB2 11 77 0.6 14 8.4 Low
QC1 8 121 0.6 7 4.2 Low
QC2 58 153 0.4 38 15.2 Medium
Table 3
Number of the sampled stems damaged by rodents
Plot B
Quadrat damgd Total counted Stratum %stem %damage
no stems stems size damgd proportion stratum
QA1 8 79 0.7 10 7 Low
QA2 11 30 0.3 37 11.1 Medium
QB1 36 75 0.3 48 14.4 Medium
QB2 22 86 0.3 26 7.8 Medium
QC1 9 79 0.7 11 7.7 Low
QC2 6 117 0.7 5 3.5 Low
Average calculated percentage damage Plot A= 11.03%, Plot B= 8.6%, damged= damaged
Formula and calculations
Average% Plot A= (Average % damged medium+ Average % damged low/2)
= (12.4+15.2+15.2/3) + (10.8+8.4+4.2/3)
= (14.3+7.8/2)
= 11.03%
Average% Plot B= (Average % damged medium+ Average % damged low/2)
= (11.1+14.4+7.8/3) + (7+7.7+3.5/3)
= (11.1+6.1/2)
= 8.6%
27

28. Wilcoxon rank sum test (table 4)
Table 4
Plot A Plot B
%stem %stem
damgd rank damgd rank
18 6 10 3
31 8 37 9
38 10.5 48 12
14 5 26 7
7 2 11 4
38 10.5 5 1
Ta 42 Tb 36
TA=total ranks of plot A, TB=total ranks of plot B
TL= test statistic lower bond, P=probability, T=test statistic
The rank sum of untreated plot A, denoted Ta, is 42. The rank sum of treated plot
B, denoted Tb, is 36. I used Wilcoxon sum rank as the test statistic. I arbitrarily
selected Tb as the test statistic and label it T. The value of the test statistic is
T=Tb=36. A small value of T indicates that most of the smaller observation(less
damage) was in plot B and that most of the larger observation (heavy damage)
was in plot A. Therefore, in order for me to conclude statistically that was the
case, I needed to show that T was small(less damage). The definition of “small”
came from the sampling distribution of T. From this sampling distribution (table
17.3b critical values of Wilcoxon rank sum test), I could see that P (T≤28) = P
(T=28) =0.05. Because I was trying to determine whether the value of the test
statistic was small enough for me to reject the null hypothesis at the 5%
significant level, I specified the rejection region as T≤28. Since T= 36 lies outside
the critical region and therefore the test is not significant so the null hypothesis is
accepted. The conclusion is that there is no evidence to reject the hypothesis that
damage in the treated plot B was the same as the damage in the untreated plot A.
Also to the calculated average % damage, it does not show a great difference.
The average %damage in plot A in table 2 was 11.03%, and plot B in table 3 was
8.6%. There was no evidence to accept that trapping rats can reduce rodent
damage.
28

29. 6.4 Discussion
6.4.1. The distribution of rodent damage
The results presented here suggest the distribution of rodent damage in millet
fields in the millet/maize growing areas of Kake village, Mukwe constituency in
Kavango region. Considerably, there was an obvious edge and center effect in
millet fields with more or conversely, less damage near the field edges and high
damage at the center as observed in other crops with rodent damage (e.g. Buckle
et al., 1985; Schaefer, 1975).The distribution of damage of damage at the fields’
levels indicate that rodents are more active at the center and less at the edge.
Dense millet fields at the center than edge may attract rats for several reasons.
The first is a response to a better cover at the center as more plants provide rats
with more protection. This unusual pattern presumably reflects aspects of
behavioural response and species involved from the rats to get as far away as
possible from the edge of the fields where they perceive "predators" (e.g. snakes,
owls, farmers, etc) are "hunting". A second possibility is related to energy
maintenance. It is more advantageous for a small mammal to reduce its foraging
radius by selecting a home range with an optimum supply of food and cover.
Reducing the amount of foraging time conserves energy expenditure, reduces the
amount of surface activity, and minimizes exposure to predators or conspecifics
than the edge. Also, greater millet density at the center may mean great carrying
capacity, larger populations, population compression, and hence, more damage
at the center than edge. In many cases, variation within the fields in soil and
vegetation cover may contribute to such clustering, and this could be affected by
e.g. land preparation methods. This corresponds in other study, that rodents can
adjust its feeding behaviour depending on prevailing local circumstances such as
cover and predation risk (Mohr, 2001). I did some radio tracking of rats in millet
crops fields at Diyogha village and found that when the millet crop provided
sufficient cover, rats were spending time in the crop during the day (we did not
29

30. know this before) as well as at night time. So there is probably a cover/predator
avoidance response. I did note, however, that the damage at the center (14.1%
average damage) was significantly to the damage at the edge (5.5% average
damage).
6.4.2 Estimation of rodent damage on millet
Rodent damage was noted in cropping season (January- April) of pearl
millet/mahangu fields in summer 2008. The average percentage of stem damage
in untreated millet (control) plot A was considerably higher on average values of
11.03% than in the treated millet plot B values of 8.6%, with no significant
difference at 5% significant level. Results shows it’s was probably true that in
general terms that more rodents produced more damage in untreated plot A. The
estimation allows describing the rodent abundance and damage. Although
untreated (control) Plot A was surrounded by fallow lands, as fallow lands also
provide suitable ground for shelter and breeding while grass and weed seeds are
supplementary food for the rodents (Mwanjabe 1993), but plot A still had high
damage. Many aspects of rodent ecology and behaviour are density dependent,
which was that rodent changed in response to changes in population density.
There was a shift in a diet from broader range of foodstuffs (grass, weeds seeds,
mahangu leafs, etc.) to one preferred food item (millet stems), as millet stems are
juicy and soft during growth stage one (GS1) and provided high-quality food
resource for the high population of rodents. The rodents do not necessarily cut
all stems from single plants in quadrats; rather they seem to move between strata
levels without spending a long time searching for fresh stem to devour.
Typically, this damage resulted in almost complete removal of millet stems at the
GS1 in plot A.
30

31. Although difference was not significant to show us evidence that that trapping
rats can reduce damage, however, treated millet field plot B had low damage
percentage than plot A. Plot B was treated by trapping rats with setting up kill
and live traps, for three consecutive nights in a month and total of 49 traps were
used. A total of 42 rats were killed. If trapping rats was done continuously
everyday in each month without giving chances for the rats to access in the field,
damage could be reduced significantly. However, trapping was done for three
consecutive nights in each month which was a great chance for the rats to get
access into the field and caused the damage. In addition, plot B had a lot of
variation in the fields such as mite hills, sandy loam soil, and was surrounded by
bushes which might have provided refuge area for breeding, explosion number
of rats and easy access to get in the field.
8. Conclusion
This study and others have demonstrated that rodent damage is highly at the
center and lowest at near or around the edge of fields; it proved the hypothesis
that state rodent damage is high at the center than edge of fields in millet crops.
For this reason, it is important to assess and monitor the rodent damage
distribution in crop fields. Mulungu et al. (2003a) reported that among other
sampling techniques, stratified sampling techniques is simpler, cheaper, easier,
and less time consuming sampling techniques for rodent damage estimation,
regardless of whether the underlying variation is discrete or continuous. The
measurement based to estimate the proportion of stem damaged by rodents,
which measures the fraction of the crop damaged and lost to rodent at
preharvest. Perhaps the most important approach for preventing rodent damage
to growing crops other than using rodenticides is to use traps to lower the rodent
population. Traps set in treated field (plot B) shows a result of less percentage
damage than untreated field (plot A). The hypothesis that state trapping rats
31

32. reduce rodent damage in millet filed was not proved but continuous trapping
rats can reduce the rodent damage in millet fields.
The development ecologically-based rodent management control is still on going
led by Natural Resource Institute of the University of Greenwich (UK).
Coordinated rodent control effort by all the farmers in an area and directed at
trapping rats continuously would also seem key for control to be cost-effective.
Fields are small and usually in various stages of expansion which allows rats to
readily move among them and concentrate in preferred situations. Farmers who
wait to conduct control in only their own fields’ risk an invasion of rats at times
their crops is most vulnerable to damage, when rat numbers are highest and
when reinvasion is most likely. Subsequent fields’ assessments have
demonstrated that the farmers in an area can successfully implement the control
strategy of trapping rats to reduce damage. It demonstrated that trapping not
only effectively reduced the population of rodents in crop fields, but with
continuous trapping also constrained population growth. Research should
continue to seek ways to reduce rodent populations and damage to agriculture.
32

33. 9. Reference:
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34. Pech R, Hood G, Singleton G, et al. 1999. Models for predicting plagues of house
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34

35. Appendixes
Appendix 1
35

36. Appendix 2
CEREAL CROP DAMAGE DATA SHEET Crop type:
Quadrat No. Site Name: District: Date: Name of Data
Recorder :
Total stems
Damage (cut stems) (uncut&cut stems)
Edge of field
Low damage
Medium
damage
Heavy damage
Center of field
Damage = number of stems cut
Designed by: Lukas Mandema
36