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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.

ECORAT PROJECT

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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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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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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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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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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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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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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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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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1

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4 56

7

8

10

20

30 4050 60

70 8090

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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.

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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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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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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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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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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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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PROJECT REPORT

PREHARVEST RODENT DAMAGE ASSESSMENT ON MILLET

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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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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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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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� 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

0H : The amount of damage in the centre is the same as that at the ages.

1H : There is more damage in the centre than at the edges.

� Trapping rats can reduce damage on millet

0H : The damage in the treated plot B is the same as that in untreated plot A.

1H : 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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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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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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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.

L

L

L

M

M

M

L

L

L

M

M

M

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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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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

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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 %damged Rank

Edge % 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% average stem damage

5.5% average stem 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 %

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 no

damgd stems

Total counted stems

Stratum size

%stem damgd

%damage 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 no

damgd stems

Total counted stems

Stratum size

%stem damgd

%damage 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%

28

Wilcoxon rank sum test (table 4) Table 4

Plot A Plot B

%stem damgd rank

%stem 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.

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

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.

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

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.

33

9. Reference:

Ahmed, M. S., M. Y. Man, M. E. Haque, and J. E. Brooks. 1986. Bandicoot rat damage in deepwater rice fields. Int. Rice Res. Newsl. 11:25. Burton, T. (1990). Bird damage near vineyards in Bendigo. In National Bird Pest Workshop Proceedings. Fleming, P., Temby, I. and Thompson, J. (eds). NSW Agriculture and Fisheries, Armidale: pp. 51–54 DeHaven, R.W. (1974a). Bird appraisal methods in some agricultural crops. In Proceedings of the 6th Vertebrate Pest Conference. Johnson, W.V. (ed.). University of California, Davis: pp. 246–248. DeHaven, R.W. (1974b). Bird damage to wine grapes in central California. In Proceedings of the 6th Vertebrate Pest Conference. Johnson, W.V. (ed.). University of California, Davis: pp. 248–252. DeHaven, R.W. and Hothem, R.L. (1979). Procedure for visually estimating bird damage to grapes. In Vertebrate Pest Control and Management Materials: 2nd Dolbeer, R.A. (1975). A comparison of two methods for estimating bird damage to sunflowers. Journal of Wildlife Management 39: 802–806 Geddes, D. (1992). Geometry in the Middle Grades. Reston, Va.: National Council of Teachers of Mathematics. (QA461 Ged) Elton C. 1942. Voles, mice and lemmings. Hertfordshire, UK: Wheldon & Wesley. Reprinted 1965 Fiedler L. 1988. Rodent problems in Europe. In: Prakash I (Ed). Rodent pest management. Boca Raton, FL: CRC Press. p 5–66. Fiedler, L.A. (1994). Rodent pest management in eastern Africa. FAO, Rome, Italy. 83pp Makundi RH, Mbise TJ, Kilonzo BS (1991). Observations on the role of rodents in crop losses in Tanzania. Beitrage Tropical landwirsch: 183–5p. Mulungu, L.S. (2003). Assessment of maize (Zea mays L.) damage and yield loss due to rodents in the field. PhD Thesis, Sokoine University of Agriculture,Morogoro,Tanzania.178p

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Pech R, Hood G, Singleton G, et al. 1999. Models for predicting plagues of house mice (Mus domesticus) in Australia. In: Singleton GR, Hinds LA, Leirs H, and Zhang Z (Eds). Ecologically-based management of rodent pests. Canberra, Australia: ACIAR. p 81–112 Poché, R. M., M. Y. Mian, M. E. Haque, and P. Sultana. 1982. Rodent damage and burrowing characteristics in Bangladesh wheat fields. J. Wildl. Manage. 46:139-147. Posamentier, H. 1981. Observations on three species of rodents in deepwater rice in Bangladesh. Z. Angew. Zool. 68:155-167. Posamentier H. 1997. Communication in national rodent management programmes. Belg J Zool 127: 171–80S Posamentier, H., and S. Alam. 1980. Rodent damage and control in wheat in Bangladesh during the 1980 season. Bangladesh J. Zool. 8:99-101

35

Appendixes

Appendix 1

36

Appendix 2

CEREAL CROP DAMAGE DATA SHEET Crop type:

Damage (cut stems)

Total 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

Quadrat No.

Site Name:

District:

Date:

Name of Data Recorder :