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Development of ecologically based rodent management for sadc region

Development of ecologically based rodent management for sadc region






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    Development of ecologically based rodent management for sadc region Development of ecologically based rodent management for sadc region Document Transcript

    • ECORAT PROJECTDevelopment of Ecologically Based Rodent Management for SADC RegionAbstractThe aim of the Ecorat project is to develop ecologically based rodentmanagement in southern Africa by investigating the rodent problems affectingsmall-scale farmers in the region. Ecologically based rodent management isincreasingly seen as more sustainable, both economically and environmentally,than the traditional use of poisons. It is therefore important to raise awarenessand gather accurate information about the health risks posed by and the extent ofthe crop damage caused by rodents in NamibiaThe Ecorat project is co-ordinated by scientists at the Natural Resources Instituteof the University of Greenwich in the UK, and involves organisations inSwaziland, Tanzania, South Africa and Namibia. The international Ecorat projectstarted with an inception workshop at the University of Greenwich in January2007, which was attended by scientists from the four countries. 1
    • 1. IntroductionAs part of training of my studies at Polytechnic of Namibia, I was recruited byECORAT project through the partner National Museum of Namibia (NMN) tohave hands on experience.. The museum is situated on three premises withadministration, curation, research, education and the library held at MuseumACRE, the display centre at Owela Museum and Alte Feste. The Museum ACREis located in 59 Robert Mugabe Avenue, in a historical building that served as thefirst school in Windhoek and was built in 1907/08 respectively.The ECORAT project started with an inception workshop at the University ofGreenwich in January 2007. The ECORAT project is investigating the rodent-pestproblems affecting small-scale farmers in southern Africa. This internationalagricultural research project started working in Namibia to develop Ecologically-Based Rodent Management for the Southern African Region. The ECORATproject is coordinated by scientists at the Natural Resources Institute (NRI) of theUniversity of Greenwich in the UK and involves organisations from Swaziland,Tanzania, South Africa and Namibia. The aim is to strengthen the generation ofappropriate, cost-effective and sustainable rodent pest management technologiesand strategies for small-scale farming in the SADC region. In Namibia field workfor monitoring rodents is taking place at Mukwe constituency in Kavangoregion.I have been stationed at Frans Dimbare Rural Youth Centre (picture 1) for fivemonths in order to undertake field work and one month at Museum ACRE fordata analyses and reports writing. Frans Dimbare Rural Youth Development andEnvironmental Centre is located 195 km east of Rundu between Andara andDivundu on the banks of the Kavango River. The roughly 100 hector plot isdominated by the river and its abundant indigenous forest. The aim of the centreis to empower unemployed rural youth of this country but more specifically, by 2
    • assisting young people in Kavango region in building health awareness,developing educational and vocational skills as well as training courses such ascomputer repairs, tailoring and agriculture (picture 1, 2&3).Pic. 1 FDYC administration Pic. 2 Computer lecturing session Pic. 3 FDYC vegetable garden2. Objectives2.1. Employer’s ObjectiveThe National Museum’s main objective is to preserve, comprehend andelucidate the material heritage of our country for the present and futuregeneration.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 3
    • 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 training2.3. 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 Activities3.1. Rodent Ecology3.1.1. Habitat utilization and inter-specific interactionsIn general, studies on rodent habitat utilisation and inter-specific interactionswere carried out by live and kill trapping of rodents at two villages, Kake andDiyogha. 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 theremoval sites, where animals are being removed. A total of 387 traps were usedin 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 (picture6) were used as bait in traps. At all sites, the traps were set before sunset andearly morning for three consecutive nights in each month of trapping session. 4
    • Pic 4. Baiting in sheman live traps Pic 5. Snap kill trap Pic 6. Bait peanutbutter&oats3.1.2. Capture methods3.1.2. (a) Trapping in the crop fields (millet field)A study site was established in a crop field (millet field) at Kake village, arrangedin grid format (picture 7) measuring 70m× 70m with 49 trapping stationsarranged at an interval of 10m between traps (picture 8). A total of three gridswere used for three consecutive nights in each trapping session. Alternation of 10snap traps and 39 Sherman live traps were used in each grid. Animals caught inSherman live traps were sacrificed and sampled for blood, tissues, endoparasitesand ectoparasites. For both animals caught in Sherman and snap traps, breedingconditions (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 bodyweight, head and body length,) of all captured specimens. Data will be analyzedfor 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 5
    • 3.1.2. (b) Trapping in houses and Peridomestics areasThe locations of traps in houses and peridomestic areas were partly directed bythe household and variations in building structure and size. Five traps were setin each peridomestic area and household. A total of 30 household were sampledin 2 villages Kake and Diyogha (15 per village). The specimens collected will beused for the diversity of the commensal rodent communities in domestic areas inrural settings, rodent abundance in rural houses and status of each species,parasites load, blood and tissues taken for pathogen determination and forpotential disease transmission to humans( test for 4 diseases-plague,Leptospirosis, toxoplasmosis, lassa fever and borelia). These studies will enablethe 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 centersThirty traps were set in each center, Frans Dimbare Youth Center and AndaraHospital. 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 ahypothesis whether the risk of contracting rodent borne diseases is directlyrelated to the magnitude occurrence of commensal rodents and the remaining 5traps are kill traps for removal and identification of abundance species at thecommunity centers.3.1.3. Procedures of processing trapped animalsLive trapped animals from the removal sites are being anaesthetised usingchemicals called chloroform. A layer of cotton wool is soaked in chloroform anddropped in a zip-lock with the animal and left for few minutes until the animal isunconscious (picture 9). 6
    • Pic 9. Staff in the project anaesthetising a specimenSoon after anaesthetising the animal, blood sample is taken from the heart orretro-orbital sinus using syringe and needle. The collected blood sample is keptin labelled eppedorf tubes and stored at the temperature of -4°C. The blood takenwill be tested for possible zoonotic diseases. Pic 10 taking blood sample from specimenThen specimens are being identified to genus or if possible to species level usinga rodent’s dichotomous keys (De Graaff 1981; Stuart 1988). From there, sex andthe reproductive status is being examined (picture 11, 12 by Krebs, C.J. 1999). Inmales, testes are being examined whether Abdominal or Scrotal (hanging), ifscrotal, it is an indication of sexually active (breeding). In females, the followingare 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 7
    • Immediately after that, the animals are brushed to remove ectoparasites. Thecollected ectoparasites are preserved in labelled eppendorf tube with 70% alcoholbefore being sent for identifications at the National Museum of Namibia.Pic 13 collecting ectoparasitesAfter removing ectoparasites, the followings measurements are being taken;body weight (g) using a Pesola spring balance as shown in picture 14, and lefthind-foot, ear, tail and head-body (mm) using a normal standard ruler.Pic 14. Body weighingFrom there the specimens are being dissected to take out tissue samples, gutcontents and for the internal reproductive status examinations (picture 15). Freshpairs of scissors and forceps dipped in 96% alcohol are being used to open theabdominal and thoracic cavity. Livers and kidneys are the tissue samples that arebeing taken, preserve them in a labeled vial with 96% ethanol and store them atthe temperature of -4°C. These samples are being sent to the Durban NaturalScience 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 forendoparasites examinations. 8
    • Pic 15 female adult specimen in secondtrimester of pregnancy with seven healthyembryosThen 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 givenindividual.Then the dissection cut is closed with a needle and a thread after tissuesampling (picture17). Carcasses are thrown in formalin solution, left for three days andtransfer them in 70% alcohol before sending them to the Durban Natural ScienceMuseum for further identification.Pic 16 closing dissection cut Pic 17 tagging specimen3.1.4. Population dynamicsPopulation dynamics studies are being carried out in two fallow lands, by usinga Capture Mark Recapture (CMR) method. These sites are at 1 km apart at Kakevillage. The traps are being set in a grid format in a plot measuring 70m× 70mwith 49 marked trapping stations arranged at an interval of 10m betweenstations. 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, 9
    • seasonality of population patterns (breeding and reproduction, survival andmobilization). Sherman live traps are being used, on each captured animal, theweight and the external breeding conditions (scrotal vs non-scrotal, perforated vsclosed 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 (picture20). Rainfall data, temperature and relative humidity are always being recordedduring processing. The data collected will be used for demographic orpopulation analyses. Preliminary analyses show that although several smallmammal genuses are represented at the study sites, by far the greater part of theanimals is Mastomys sp a small amount of saccotomys sp is also found in two ofthe study sites, Generally speaking the population dynamic patterns andreproduction of both Mastomys sp. and saccotomys sp. show seasonality, and mayrelate to the rainfall pattern, although more data are needed for properinterpretation. 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 mark4. Rodent-Human InteractionsThe main objective of this study is to assess habitat utilization and overlappingresources uses between rodents and human. Techniques such as radio telemetryand spooling can be used to study the movements of animals. For this study,radio telemetry was used. Telemetry involves attaching small radio collars toanimals and monitoring their movements with a handheld receiver. This 10
    • research will help establish the degree to which different rodent species come tocontact with areas of human settlement and the potential interaction betweendifferent rodent species utilizing the same habitat. One species (Mastomysnatalensis) was selected for the radio telemetry study. Three sessions, pre-harvest(food abundantly available in the field), post-harvest (food available in grainstorage), and pre-planting (little food available in the field), are to be conductedfor this study. The first session was conducted during my In-service Trainingperiod (picture 21-23).Six individuals were captured in different habitats, collared and released at thecapture points. Radio tracking started the following day after the release and theanimals were tracked for five nights in different time intervals (17h00-21h00,21h00-01h00 and 01h00-05h00). Radio-tracking involved taking fixes at 10 minuteinterval (when the animal is not moving) and 2 minutes (when the animal ismoving). At each fix, GPS, time and compass reading are recorded and thehabitat noted. The receiver was used to pick up the signal being emitted by thetransmitters attached on the animals tracked. Pic 21 ready to radio track Pic 22 finding day roost Pic 23 radio-tracking in the night 11
    • 5. AdministrationAdministration work is also part of the duties in the ECORAT research project. Iwas involved in acquiring quotations from different companies. Once allquotations are received, prices are compared and one company is recommended,the selected company receives an order form in return for goods and an invoiceis then payout. As a research trainee, I was entering the data in the excel sheetand writing of monthly reports on how we are using the fuel, kilometerstravelled and meetings held with the communities.As a trainee, I designed a leaflet about ECORAT research project, how it wasinitiated, where and when, aims, the activities of the project, the partnersinvolved in the project and the funding source.6. Community meetings and presentationsIn January 2008, Capture-Mark and Recapture (CMR) plot 1 was cleared forploughing by the owner of the field. The plot was identified as a fallow landbefore the beginning of the Ecorat research and a permission to use the plot forCMR study was granted to Ecorat by one of the member who claimed to be theowner. Ecorat staffs discovered the situation and called a meeting which washeld at Diyogha village (picture 24). The meeting involved two headmans (fromKake and Diyogha), the former and current owner of the field and otheradditional members of the community. At the end of the meeting an agreementwas reached between the real owner and Ecorat that the owner should becompensated. Picture 24 shows the community meeting 12
    • 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 ResearchProject. I presented my research about Rodent Damage Assessment in milletfields, the purpose and the expected outcomes. Ecorat staffs explained how theproject started, aim of the project, activities of the project and the donors.7. Reflection on the duty station and ECORAT staff teamworkI honestly liked the teamwork of the project coordinator and the two ECORATresearch technicians I worked with during the period of my training. I foundthem to be hard working, inventive and people of awe-inspiring working withand I learned a lot from them. Though I was a research trainee, staff members atFrans Dimbare Youth Centre regarded me as a well disciplined person, a personwho is willing to learn, mental alert and likes bringing up creative things whichwas very useful to the youth, community and staff members. I learned more onwriting scientific reports, research project, gained scientific experience, andradio-tracking which I thought I will never know in my life, processing smallmammals and toe clipping of live animals. The research exposed me to workwith many communities learning the culture and religious of those communitiesand it was so beautiful to adapt with them. Generally, I would say the staffmembers of my two duty stations Frans Dimbare youth centre and Nationalmuseum have very good personalities, a sense for cooperation and devotion totheir work. 13
    • 8. ConclusionsIn my personal point of view, Frans Dimbare Youth centre is not a very perfectduty station for research purposes because it lacks some standard for a researchstation, not having a library, internet and communication is not that accessible.However, it was fine with ECORAT research project because they chose localvillage near the center for the research. The project provided a car, tents, lightsand a computer for storing the data but it did not provide internet. During mytraining I mainly became involved with the research work of trapping, radio-tracking, capture and mark study, data entry, assessing damage in millet fieldsand writing monthly reports. Within six months, I could conclude that ECORATproject is a scientific project which is researching on pest management control inagriculture. Working at the National Museum with ECORAT project, enhancedmy understanding of damage caused by rodents and possible diseases that canbe passed to humans by the rodents. During the six months period I gainedexperience 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 chemicalsolution preparation and taxonomic identification of rodent species. Generally,the two duty stations have very good working environment and the two researchtechnicians work very hard to attain the mission statement of the ECORATresearch project. I enjoyed every single hour of my work during my training atthe two duty stations and I have no doubt regarding my further research andwork as a permanent agricultural research technician. 14
    • 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, 620p3. Stuart, C.T. & Stuart M.D. 1988. Field guide to the mammals of Southern Africa. Cape Town: Struik Publisher 15
    • AbstractIn this study the aimed was to assess preharvest rodent damage on millet. Thestratified random sampling technique was used to provide data to achieveprecision and accuracy in estimations of rodent damage in millet fields at theplanting and preharvest stage. The rodent damage distribution was divided instrata 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 wereused to the estimate the distribution of damage and estimation in millet fields,using quadrates that would provide precision and accuracy. Wilcoxon rank sumtest was used to find the significant difference for damage distribution andestimation. The results of this study show that the distribution of damage is ahigh at the centre than edges of millet fields. The heterogeneous distribution ofdamage in plots caused variations in the accuracy of the estimates between plots,but trapping rats in plot B produced estimates with average percentage damagevalues of 8.6% than untreated plot B values of 11.03%. Wilcoxon rank sum testtable and critical value table was provided to allow a hypothesis to be acceptedbased on the significant difference and on the distribution of damage andestimation as a function of required precision using the stratified randomsampling technique in millet fields.Key words: critical value, distribution, estimation, hypothesis, preharvest,quadrates, rodents, strata, stratified random sampling technique, Wilcoxon ranksum test. 17
    • 1. IntroductionRodent damage to crops is a serious obstacle in agriculture (Fiedler, 1988;Singleton et al. 1999). Preharvest damage to cereal crops is a chronic problem inthe world. Losses are reported to be substantial (Ahmed et al., 1986; Poche et al.,1982; Posamentier & Alam 1980; Posamentier 1981,). Farmers in many parts ofthe world, particularly those in developing countries, tend to view economiclosses due to rats and mice as unavoidable (Posamentier 1997; Singleton et al.1999). In fact, the impact of rodents has been greatly underestimated andgenerally ignored in the general scientific literature, with a small number ofexceptions (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 , therodent 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 theindividual fields.Pic 1. Freshly sown seeds dug by rodents Pic 2. Shows refuge or burrow for rodents in a fieldRodent damage effects in agriculture are complex because almost all crops arethe target of rodent attack (Fiedler, 1988; Singleton, 1999). Rodents areresponsible for considerable damage to food and play an important role asreservoirs and carriers of zoonotic diseases. Survey reports in Tanzania, fromempirical data have shown that on the average, rodents caused about 15% loss of 18
    • maize crop annually (Makundi et al., 1991). In Indonesia, rodents are the mostimportant 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 andmillet in their fields particularly small-scale farmers. The present study providesthe first information on the damage distribution, the magnitude and extent ofpreharvest losses in Namibia. Millet production in Namibia is increasinglypopular among small-scale farmers. Millet is well adapted Namibian stapledrought resistance crop, as Namibia is a semi-desert country. Maize is moredifficult to cultivate for small- scale farmers because it requires frequentirrigation or rainfall, most of which is done by hand and on commercial. Milletrequires little cultivation and watering after broadcasted.In this study, I investigated the rodent damage distribution, damage estimationand effect of stem cutting on preharvest yield on millet using stratified randomsampling 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 theedges 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 bushes3. Personal Objective To understand the relationship between the growth stages and intensity of crop damage 19
    • 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 agriculture4. 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 Methods5.1. Study plots and areaThe study was conducted at Kake village near Divundu. Divundu is situatedabout 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 thefive kingdoms in the Kavango region. As most parts of Namibia, farming in thisregion is all subsistence, with farmers owning an average of 1 to 5 ha of cropfields per household. Two millet fields sites were selected both at Kake village,millet field site (Plot A), was part of monoculture millet field surrounded byfallow 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 loamsoil. The other millet field site (plot B) was located in mosaic landscape of milletfield surrounded by bushes (picture 4), sited at 18° 05’ 20.1”S, 21° 30’ 28.8”E at an 20
    • altitude of 1019m. Predominantly soil type is sandy loam soil. The study wasconducted during the cropping season which is also the main millet/mahangugrowing season (January-April 2008). The study size plots of 70m x 70 each werelocated in each two field sites. The plots were at least 600m apart, so that none ofthe two millet fields influence the rodent population of the other field. The seedwere sown in late January, and assessed early second week of February until thelate second week of April in both fields. The experiment was carried out everysecond week for a total of four months in each plot. The millet seeds werebroadcasted and manual weeding was carried out once in both fields.Pic 3 Plot A surrounded by fallow land Pic 4 Plot B surrounded by bushes5.2. Sampling proceduresTwo 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. Inmillet crop field, the distribution of damage within each field was highlyvariable. A stratified sampling technique (Mulungu, 2003) was used in bothfields of 70m x 70m each, where rodent damage was heterogeneous (i.e. notrandomly distributed but higher in some zones than in others). The samplingprocedure for stratified random sampling begun with the definition of thestrata—the damage levels within the millet fields. Estimates were madeseparately in each of these zones and were combined taking the relative size ofeach strata into account. One goal of stratification was to create sub-universes 21
    • that are uniform internally, i.e. to minimize variation within strata andmaximimize variation among strata. Visual estimation was rapid and is themethod most widely used to obtain distribution of rodent damage to agriculturalcrops (Stevenson and Virgo 1971; DeHaven 1974a; Dolbeer 1975; DeHaven andHothem 1979). This was achieved by assigning a damage ranking strata withinthe each field.During the study, within each stratum a quadrate of 1m2 was randomly selectedin areas of similar damage intensity. A total of six quadrates were used in eachplot 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 eachstratum in each crop field was determined by visual estimates of how much thestratum occupy per field. In plot A, stratum of low occupied 60% and medium40% and four quadrates were set up in low stratum and two quadrates inmedium. In plot B, stratum of low occupied 70%, medium 30% and threequadrates were set in stratum of low, three quadrates in stratum of medium. Thequadrat setups were depending on the variability of rodent damage levels in thefield. The more quadrats number per field the more precision. Nevertheless, ithas been reported that at least five quadrats within at field of 70m x 70m areenough as a sample size. In both study fields, six quadrats were set up within atfield of 70x 70m. The quadrats within each study plot were plotted on the map tovisually verify where in each field distribution would have occurred (picture 4-5). 22
    • 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 mZigzag line is the stratum boundary, L =Low M=medium =quadrat5. 3. Distribution of damageAssessing the damage caused by rodent on millets fields was an important toolto quantify damage estimation and distribution of damage. Assessment of ratdamage and distribution was performed in two millet fields of 70m x 70m eachwith varying degree of rat damage. Both millet fields were superficially surveyedby visualizing stem distribution damage caused by rodents, at a seedling stage,10 days after planting. The distribution of damage was identified by walkingacross each field and assessed the rodent stem damage. The stem is defined asthat portion of the plant that gives rise to a panicle (i.e. seed head). Cut stemswere widely distributed in both millet fields (Plot A and Plot B) as wereundetectable in low damage stratum during cursory examinations. Moderatedamage was visually seen as patches of the heavily damaged plants surroundedby areas of relatively light damage (Buckle, A.P. 1994). Heavy damaged stratumin both fields was not observed; only two strata were assessed (low and mediumdamage, picture 7-8). In each field, one quadrate was set in the center and one atthe edge and total of four quadrates were examined. The total of stems and thenumber of rat damaged stems were enumerated within each quadrate and thepercentage damage was determined for center and edge. 23
    • Pic 7 shows medium damaged quadrat Pic 8 shows low damage quadratTo give the percentage damage, the two center quadrates in both fields weresummed up and ranked; also the same was applied to the quadrates at the edgesof the two fields. Percentage of the stem damage at the center and edge wascompared. Near the edge of the field (i.e. around the perimeter of the field) ofeach field were not sampled because of frequent goat damage and preventsampling of abnormal damage in relation to barriers. The Wilcoxon rank sumtest, which is a non-parametric technique, was used to compare the distributionsand testing hypotheses concerning the damage distribution in fields. I chose thistechnique because I was not sure whether the data was normally distributed ornot.5.4. Rodent crop damage estimationCrop damage in plot A and plot B was assessed from the first week of February2008 to second last week of April 2008, counting the number of freshly cut stemsand uncut stems every second week in each quadrat set in the strata (fig 8). Sixquadrats were in each plot of 70m x 70m and divided according to theproportion of the stratum size. The information was recorded on a standarddamage assessment data sheet I designed (see appendix 1). Estimates werecalculated by counting the number of damaged and undamaged samples withina crop. Although counting has been used to estimate total damage, a commonuse of this method is to calibrate visual estimation methods (Stevenson andVirgo 1971; DeHaven and Hothem 1979; Somers and Morris 2002).The number of stems cut for the desire intensity of damage was computed as: 24
    • D = n/N x 100Where, D = % number of stems cut n = number of stems cut N = total numbers of stemsEstimated mean percentage proportion damaged averaged over all strata(pˆST):= sum of stratum size × average proportionThe proportions of damaged stems to undamaged stems in a sample ofindividual plants were used as an estimate of the damage to millet. After theestimation, the mean percentage stem damage in millet field sites of untreatedand treated compared.Pic 9 shows cut stems by rodents in a quadrat Pic 10 counting cut and uncut stems in qudrat 25
    • 6. Results6.1. The distribution of rodent damageWilcoxon 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 damageDamgd= damaged, TC = total ranks of center, TE = total ranks of edgeSignificance level, α =0.05Number of observation per sample= 12Smallest sum of ranks= 106Largest sum of ranks= 196Critical region (5%) is "D ≥1.645"Critical region (1%) is "D ≥2.33"Calculated statistic, D = 2.568The calculated statistic, D, lie within the critical region and therefore the test isstatistically significant at the 5% level so null hypothesis is rejected. Theconclusion is that there is more damage at the center than the edges. Resultsindicate that the distribution of damage appeared to be relatively high at thecenter than the edge (table 1), regardless whether it was in monoculture ormosaic field. The same conclusion is also made at the 1% level of significance. Itaccepted the hypothesis that states Rodent damage is high at the center thanedge of millet fields. The average percentage stem damage values of 5.5% foredge and 14.1% for center. The results show a great average difference of 8.6 % 26
    • stem damage between center and edge. The occurrence of distribution stemdamaged for two fields sampled from seedling to preharvest revealed that the14. 1% stem damaged at the center of fields predominated 5.5% stem damaged atthe edge. In general, the distribution of damage of damage at the fields’ levelsindicates that rodents are more active at the center and less at the edge.6.2. Estimation of rodent damage on milletTable 2 Number of the sampled stems damaged by rodents Plot AQuadrat damgd Total counted Stratum %stem %damageno stems stems size damgd proportion stratumQA1 14 78 0.6 18 10.8 LowQA2 30 97 0.4 31 12.4 MediumQB1 18 47 0.4 38 15.2 MediumQB2 11 77 0.6 14 8.4 LowQC1 8 121 0.6 7 4.2 LowQC2 58 153 0.4 38 15.2 MediumTable 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 LowAverage calculated percentage damage Plot A= 11.03%, Plot B= 8.6%, damged= damagedFormula and calculationsAverage% 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
    • Wilcoxon rank sum test (table 4)Table 4Plot A Plot B%stem %stemdamgd 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 1Ta 42 Tb 36TA=total ranks of plot A, TB=total ranks of plot BTL= test statistic lower bond, P=probability, T=test statisticThe rank sum of untreated plot A, denoted Ta, is 42. The rank sum of treated plotB, denoted Tb, is 36. I used Wilcoxon sum rank as the test statistic. I arbitrarilyselected Tb as the test statistic and label it T. The value of the test statistic isT=Tb=36. A small value of T indicates that most of the smaller observation(lessdamage) 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 thecase, 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 (table17.3b 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 teststatistic 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 outsidethe critical region and therefore the test is not significant so the null hypothesis isaccepted. The conclusion is that there is no evidence to reject the hypothesis thatdamage 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 was8.6%. There was no evidence to accept that trapping rats can reduce rodentdamage. 28
    • 6.4 Discussion6.4.1. The distribution of rodent damageThe results presented here suggest the distribution of rodent damage in milletfields in the millet/maize growing areas of Kake village, Mukwe constituency inKavango region. Considerably, there was an obvious edge and center effect inmillet fields with more or conversely, less damage near the field edges and highdamage at the center as observed in other crops with rodent damage (e.g. Buckleet 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 ratswith more protection. This unusual pattern presumably reflects aspects ofbehavioural response and species involved from the rats to get as far away aspossible from the edge of the fields where they perceive "predators" (e.g. snakes,owls, farmers, etc) are "hunting". A second possibility is related to energymaintenance. It is more advantageous for a small mammal to reduce its foragingradius by selecting a home range with an optimum supply of food and cover.Reducing the amount of foraging time conserves energy expenditure, reduces theamount of surface activity, and minimizes exposure to predators or conspecificsthan the edge. Also, greater millet density at the center may mean great carryingcapacity, larger populations, population compression, and hence, more damageat the center than edge. In many cases, variation within the fields in soil andvegetation cover may contribute to such clustering, and this could be affected bye.g. land preparation methods. This corresponds in other study, that rodents canadjust its feeding behaviour depending on prevailing local circumstances such ascover and predation risk (Mohr, 2001). I did some radio tracking of rats in milletcrops fields at Diyogha village and found that when the millet crop providedsufficient cover, rats were spending time in the crop during the day (we did not 29
    • know this before) as well as at night time. So there is probably a cover/predatoravoidance 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% averagedamage).6.4.2 Estimation of rodent damage on milletRodent damage was noted in cropping season (January- April) of pearlmillet/mahangu fields in summer 2008. The average percentage of stem damagein untreated millet (control) plot A was considerably higher on average values of11.03% than in the treated millet plot B values of 8.6%, with no significantdifference at 5% significant level. Results shows it’s was probably true that ingeneral terms that more rodents produced more damage in untreated plot A. Theestimation allows describing the rodent abundance and damage. Althoughuntreated (control) Plot A was surrounded by fallow lands, as fallow lands alsoprovide suitable ground for shelter and breeding while grass and weed seeds aresupplementary food for the rodents (Mwanjabe 1993), but plot A still had highdamage. 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 arejuicy and soft during growth stage one (GS1) and provided high-quality foodresource for the high population of rodents. The rodents do not necessarily cutall stems from single plants in quadrats; rather they seem to move between stratalevels without spending a long time searching for fresh stem to devour.Typically, this damage resulted in almost complete removal of millet stems at theGS1 in plot A. 30
    • Although difference was not significant to show us evidence that that trappingrats can reduce damage, however, treated millet field plot B had low damagepercentage than plot A. Plot B was treated by trapping rats with setting up killand live traps, for three consecutive nights in a month and total of 49 traps wereused. A total of 42 rats were killed. If trapping rats was done continuouslyeveryday in each month without giving chances for the rats to access in the field,damage could be reduced significantly. However, trapping was done for threeconsecutive nights in each month which was a great chance for the rats to getaccess into the field and caused the damage. In addition, plot B had a lot ofvariation in the fields such as mite hills, sandy loam soil, and was surrounded bybushes which might have provided refuge area for breeding, explosion numberof rats and easy access to get in the field.8. ConclusionThis study and others have demonstrated that rodent damage is highly at thecenter and lowest at near or around the edge of fields; it proved the hypothesisthat 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 damagedistribution in crop fields. Mulungu et al. (2003a) reported that among othersampling 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. Themeasurement based to estimate the proportion of stem damaged by rodents,which measures the fraction of the crop damaged and lost to rodent atpreharvest. Perhaps the most important approach for preventing rodent damageto growing crops other than using rodenticides is to use traps to lower the rodentpopulation. Traps set in treated field (plot B) shows a result of less percentagedamage than untreated field (plot A). The hypothesis that state trapping rats 31
    • reduce rodent damage in millet filed was not proved but continuous trappingrats can reduce the rodent damage in millet fields.The development ecologically-based rodent management control is still on goingled by Natural Resource Institute of the University of Greenwich (UK).Coordinated rodent control effort by all the farmers in an area and directed attrapping 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 toreadily move among them and concentrate in preferred situations. Farmers whowait to conduct control in only their own fields’ risk an invasion of rats at timestheir crops is most vulnerable to damage, when rat numbers are highest andwhen reinvasion is most likely. Subsequent fields’ assessments havedemonstrated that the farmers in an area can successfully implement the controlstrategy of trapping rats to reduce damage. It demonstrated that trapping notonly effectively reduced the population of rodents in crop fields, but withcontinuous trapping also constrained population growth. Research shouldcontinue to seek ways to reduce rodent populations and damage to agriculture. 32
    • 9. Reference:Ahmed, M. S., M. Y. Man, M. E. Haque, and J. E. Brooks. 1986. Bandicoot ratdamage in deepwater rice fields. Int. Rice Res. Newsl. 11:25.Burton, T. (1990). Bird damage near vineyards in Bendigo. In National Bird PestWorkshop Proceedings. Fleming, P., Temby, I. and Thompson, J. (eds). NSWAgriculture and Fisheries, Armidale: pp. 51–54DeHaven, R.W. (1974a). Bird appraisal methods in some agricultural crops. InProceedings 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. InProceedings 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 birddamage to grapes. In Vertebrate Pest Control and Management Materials: 2ndDolbeer, R.A. (1975). A comparison of two methods for estimating bird damage tosunflowers. Journal of Wildlife Management 39: 802–806Geddes, D. (1992). Geometry in the Middle Grades. Reston, Va.: National CouncilofTeachers of Mathematics. (QA461 Ged)Elton C. 1942. Voles, mice and lemmings. Hertfordshire, UK: Wheldon & Wesley.Reprinted 1965Fiedler L. 1988. Rodent problems in Europe. In: Prakash I (Ed). Rodent pestmanagement. Boca Raton, FL: CRC Press. p 5–66.Fiedler, L.A. (1994). Rodent pest management in eastern Africa. FAO, Rome, Italy.83ppMakundi RH, Mbise TJ, Kilonzo BS (1991). Observations on the role of rodents incrop losses in Tanzania. Beitrage Tropical landwirsch: 183–5p.Mulungu, L.S. (2003). Assessment of maize (Zea mays L.) damage and yield loss due torodents in the field. PhD Thesis, Sokoine University ofAgriculture,Morogoro,Tanzania.178p 33
    • Pech R, Hood G, Singleton G, et al. 1999. Models for predicting plagues of housemice (Mus domesticus) in Australia. In: Singleton GR, Hinds LA, Leirs H, andZhang Z (Eds). Ecologically-based management of rodent pests. Canberra, Australia:ACIAR. p 81–112Poché, R. M., M. Y. Mian, M. E. Haque, and P. Sultana. 1982. Rodent damage andburrowing characteristics in Bangladesh wheat fields. J. Wildl. Manage. 46:139-147.Posamentier, H. 1981. Observations on three species of rodents in deepwater rice inBangladesh. Z. Angew. Zool. 68:155-167.Posamentier H. 1997. Communication in national rodent management programmes.Belg J Zool 127: 171–80SPosamentier, H., and S. Alam. 1980. Rodent damage and control in wheat inBangladesh during the 1980 season. Bangladesh J. Zool. 8:99-101 34
    • AppendixesAppendix 1 35
    • Appendix 2CEREAL 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 fieldLow damageMediumdamageHeavy damageCenter of fieldDamage = number of stems cutDesigned by: Lukas Mandema 36