University f Nebraska - Lincln DigitalCmmns@University f Nebraska - Lincln Bird Cntrl Seminars Prceedings Wildlife Damage Management, Internet Center fr 10-1983 SCARING OF CARRION CROWS (CORVUS CaRONE CaRONE) BY SPECIES-SPECIFIC DISTRESS CALLS AND SUSPENDED BODIES OF DEAD CROWS Luzia Naef-Daenzer Swiss Ornithlgical Statin Fllw this and additinal wrks at: http://digitalcmmns.unl.edu/icwdmbirdcntrl Naef-Daenzer, Luzia, "SCARING OF CARRION CROWS (CORVUS CaRONE CaRONE) BY SPECIES-SPECIFIC DISTRESS CALLS AND SUSPENDED BODIES OF DEAD CROWS" (1983). Bird Cntrl Seminars Prceedings. 263. http://digitalcmmns.unl.edu/icwdmbirdcntrl/263 This Article is brught t yu fr free and pen access by the Wildlife Damage Management, Internet Center fr at DigitalCmmns@University f Nebraska - Lincln. It has been accepted fr inclusin in Bird Cntrl Seminars Prceedings by an authrized administratr f DigitalCmmns@University f Nebraska - Lincln.
SCARING OF CARRION CROWS (CORVUS CaRONE CaRONE) BY SPECIES-SPECIFIC DISTRESS CALLS AND SUSPENDED BODIES OF DEAD CROWS 91 Luzia Naef-Daenzer Schutzenfeld, Switzerland This study was carried ut at the Swiss Ornithlgical Statin in Sempach, Switzerland. It was part f a prject n the preventin f bird damage in agriculture, spnsred by the Swiss Federal Department f Agriculture. INTRODUCTION In Switzerland, carrin crws can cause cnsiderable damage t spruting crn fields when feeding n the germinated crn. I tried t evaluate a methd t prevent these damages. The use f species-specific distress calls, fr the first time described by Frings and Jumber (1954), seemed t be the mst prmising methd. Agrnmes and bilgists have applied it in field studies t several different bird species causing damage in agriculture and n airprts (e.g., Gramet, 1962; Brugh, 1968). Hwever, the literature either describes single actins r several different scaring devices being used tgether. T be able t judge the methd, quantitative infrmatin abut reductin f damage, habituatin, and sme practical infrmatin abut the cnstructin f an effective apparatus was needed. PILOT STUDY By chsing a rubbish dump fr the first pilt study, an attractive fd surce fr crws where mre cnstant cnditins can be expected, I tried t minimize the drawbacks f an experiment n a crn field. The pilt study was carried ut in March 1980. Ten t 20 crws are regularly present at the dump, where they feed, repse, and als shw scial behavir. In the first part f the pilt study, the undisturbed crws at the dump were bserved fr tw days. In the secnd part, distress calls were emitted fr 20 t 30 secnds frm the edge f the dump as sn as a crw was abut t land in the dump fr eight cnsecutive wrkdays. Because f increased human activity in the rubbish dump in the afternns, bservatins were carried ut frm 0700 t nn. Figure 1 shws the frequency f the number f crws bserved per 5-minute interval in the cntrl phase and in the experimental phase. The median f the number f crws bserved was seven during the cntrl phase and zer during the experimental phase (difference highly significant, Klmgrff-Smirnff, p = 0.001). The time elapsed befre the crws returned t the dump after having been scared away by distress calls became lnger after every emissin f the call (Figure 2). This trend f a psitive crrelatin was bserved in bth weeks f the experiment. After the weekend the time elapsed was as shrt as in the first week and then increased again. If habituatin had ccurred, an ppsite trend wuld have been bserved. S the emissin f a ttal f nly 13 species-specific distress calls was successful in keeping the crws frm the rubbish dump, a very attractive fd surce, fr the
92 mrnings f eight cnsecutive days. The experiment was ended befre any sign f habituatin had been bserved. FIELD STUDY In May 1981 the methd f species-specific distress calls was used in a field experiment n spruting crn fields. Cnsidering the results f the pilt study, I expected the species-specific distress calls t be an effective methd in scaring the carrin crws frm the fields. The duratin f the experiment wuld be lnger than the pilt study had been; crn fields cnstitute a much less attractive fd surce fr the crws than the rubbish dump. The apparatus cnsisted f a timber which regulated the duratin f the bradcasting intervals (25 minutes OFF, 20-30 secnds ON); the cries were bradcast frm a waterprf tape recrder by tw ludspeakers frm dawn t dusk. In the same field experiment anther scaring methd, suspended bdies f dead crws (seven per hectare, 1.5 meters abve grund), was evaluated. In Switzerland this methd is frequently used by farmers. The experiments were carried ut n 12 paired triplets f crn fields (= 36 fields). The fields were all very susceptible t crw damage. They had an average size f ne hectare, and the fields f ne triplet were within an average distance f tw kilmeters. In each triplet, ne randmly selected field was treated with distress calls, ne with suspended bdies f dead crws, and ne was untreated fr cmparisn. The treatments started with the spruting f the plants and ended after 10-18 days when the plants had abut six leaves. Damages were cunted n each field every three-fur days n marked duble rws f crn which had a ttal length f 1000 meters and were at regular intervals ver the field. The three different treatments were cmpared with the multiple cmparisn f Wilcxan and Wilcx (Sachs, 1978). The fields treated with distress calls had significantly less damage than the fields treated with the dead crws and the untreated fields (p = 0.05); n difference was fund between the amunt f damage n the untreated fields and the fields with the dead crws. On all fields, hwever, very little damage ccurred. Eighty-three percent f the fields with dead crws r n treatment had less than 0.05% damage (100% = average density f plants), 62 % had less than 0.1 % damage. Sme bservatins abut the ccurrence f damages n the fields culd be made. Figure 3 shws the relatinship between damage and spruting date f crn; the tw squares deviate remarkably frm the rest f the paints. These were the nly tw fields which were flded fr sme time befre spruting. Extreme wetness seems t be a reasn fr crw damage. Omitting these tw paints, a highly significant crrelatin between damages and spruting date was fund (r = 0.99; P = 0.001). There was als a highly significant psitive crrelatin between damage and duratin f perid susceptible t damage, as well as a significant negative crrelatin between spruting date and duratin f perid susceptible t damage. The partial crrelatin cefficient between spruting date and damage, mitting duratin f damage susceptible perid, is r = 0.9584 (p = 0.001). The ther partial crrelatin cefficient (damage and duratin f susceptible perid, mitting spruting date) is nt significant. It therefre was cncluded that the imprtant influencing factr fr damages was the spruting date. Distress calls prved t be a very effective methd t keep carrin crws frm spruting crn fields, while suspended bdies f dead crws had n scaring effect. With distress calls, the chsen intervals f 25 minutes with 20-30 secnds bradcasting prved t be apprpriate. Amng the factrs influencing crw damage n crn fields, the mst imprtant was extreme wetness. Anther factr f imprtance was the date f spruting f the plants. A pssible reasn fr this is that earlier in the year crws find less fd, which causes them t search the grund and frage n all pssible surces; pen arable land is frequently visited as it ffers much insect fd.
93 LITERATURE CITED Brugh, T. 1968. Recent develpments in bird scaring n airfields. pp 29-38, In R.K. Murtn and E.N. Wright (eds.), The prblems f birds as pests. Academic Press, Lndn and New Yrk. Frings, H. and J. Jumber, 1954. Preliminary studies n the use f a specific sund t repel starlings frm bjectinable rsts. Science 119: 318-319. Gramet, PH. 1962. L'effaruchement acustique par diffusin de cris de detresse applique a la prtectin des cultures cntre les deg'ihs de Crbeaux. Annales des epiphyties 13: 111-117. Sachs, L. 1978. Angewandte Statistik. Springer Verlag. Berlin, Heidelberg, New Yrk.
e.g CONTRa... PHASE... Z E E In 0.1 Q,. Q,. CI'I CI'I X.08 U! "- 0.J. a "- 0 10' 30 4C number f... Z In U a -M. EXPERII NTAL PHASE 40 n number f Crws FIGURE 1. Frequency f the number f crws per five minutes
...J mnl y.31.5x -35.7 300 240... 1 g...!... ",1...J 60 Z g... FIGURE 2. first week secnd week 0 2 3 4 5 6 7 NUMBER OF DISTRESS CALL Time elapsed until crws returned t dump (rdinate) and number f distress call DAMAGE 700 r- 500 150 100 50 FIGURE 3. y=140.5x-4.64 '. O. 0:6 ' 0:8' '1 l/sprouting DATE Crrelatin between damage and 1/spruting date. Crrelatin highly significant (r = 0.99, P = 0.001). CD 01