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Using conditioned food aversions to protect blueberries from birds: Comparison of two carbamate repellents
Applied Animal Behaviour Science, 13 (1984/85) 383--386 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands
383
USING CONDITIONED FOOD AVERSIONS TO PROTECT BLUEBERRIES FROM BIRDS: COMPARISON OF TWO CARBAMATE REPELLENTS
MICHAEL R. CONOVER Department of Ecology and Climatology, The Connecticut Agricultural Experiment Station, Box 1106, New Haven, CT 06504 (U.S.A.) (Accepted for publication 7 June 1984)
ABSTRACT Conover, M.R., 1985. Using conditioned food aversions to protect blueberries from birds: comparison of two carbamate repellents. AppL Anim. Behav. Sci., 13: 383--386. This study compared the effectiveness of two carbamate repellents (trimethacarb and methiocarb) in protecting blueberry fields from fruit loss caused by birds (primarily Northern Mockingbirds, European Starlings and Northern Orioles). Methiocarb and trimethacarb reduced berry loss significantly in the treated plots by 25 and 52%, respectively, during the first week after application. Differences between the two repellents in effectiviness, however, were not statistically significant. Moreover, neither repellent reduced berry loss significantly in adjacent untreated plots. These results indicate that both repellants caused birds to avert only from treated berries, and not from the taste or sight of blueberries themselves.
INTRODUCTION C o n d i t i o n e d f o o d aversions o f f e r ranchers, f a r m e r s a n d wildlife m a n a g e r s a n e w t o o l f o r alleviating specific p r o b l e m s caused b y animals ( C o n o v e r , 1 9 8 1 ) . One o f t h e m o s t successful uses o f aversive c o n d i t i o n i n g has b e e n t h e alleviation o f bird d a m a g e t o small fruit b y using m e t h i o c a r b ( 3 - 5 - d i m e t h y l 4-methylthiophenol methylcarbamate), produced by the Mobay Chemical C o r p o r a t i o n as Mesurol. M e t h i o c a r b has r e d u c e d bird d a m a g e t o b o t h ripening b l u e b e r r i e s ( S t o n e et al., 1 9 7 4 ; C o n o v e r , 1 9 8 2 ) a n d cherries ( G u a r i n o et al., 1 9 7 3 , 1 9 7 4 ) , a n d has gained clearance for such use b y t h e U.S. Envir o n m e n t a l P r o t e c t i o n A g e n c y . A l t h o u g h e f f e c t i v e in r e d u c i n g bird d a m a g e t o t h e s e fruit, m e t h i o c a r b has t w o d r a w b a c k s : (1) its e x p e n s e {costing a b o u t $ 1 3 2 h a -1 w h e n applied at an e f f e c t i v e r a t e o f 3.0 kg h a - l ) ; (2) its d e t e c t a b i l i t y o n s p r a y e d fruit, causing birds t o a v e r t f r o m its t a s t e r a t h e r t h a n f r o m t h e f r u i t itself ( C o n o v e r , 1 9 8 2 ) . H e n c e , birds can r e t u r n t o a s p r a y e d o r c h a r d a f t e r t h e r e p e l l e n t has w a s h e d o f f , or cause d a m a g e in n e a r b y u n t r e a t e d orchards (Conover, 1984). T h e goal o f this s t u d y was t o t e s t a n d c o m p a r e t h e ability o f m e t h i o c a r b 0168-1591/85/$03.30
© 1985 Elsevier Science Publishers B.V.
384 and a new carbamate repellent, trimethacarb (UC 27867), to reduce bird damage to both treated and nearby untreated plots of blueberries. Trimethacarb, made by Union Carbide, contains a mixture of 3,4,5- and 2,3,5-trimethylphenyl carbamate. It already has been used successfully to establish conditioned taste aversions in domestic ducks (Gustavson and Basche, 1983) and American Crows, Corvus brachyrhynchos (Nicolaus et al., 1983). METHODS These experiments were conducted during 1982 and 1983 at both the Connecticut Agricultural Experiment Station's farm in Hamden, where these repellents were tested on a 0.05-ha blueberry planting consisting of 7 highbush blueberry varieties (Concord, Pemberton, Weymouth, Atlantic, Jersey, Dixie and Burlington), and at Rose's Berry Farm in Glastonbury, CT, where five 0.4--1.0-ha field were used. Each field consisted of one of the following varieties: Berkley; Blue Crop; Bluetta; Darrow; Patriot. The major bird pests in these blueberry fields (Conover, 1982) were Northern Mockingbirds (Mimus polyglottos), Northern Orioles (Icterus galbula), American Robins (Turdus migratorius) and European Starlings (Sturnus vulgaris). Bird damage was monitored in each plot by marking clumps of 10 berries with small strings to facilitate later identification. At least 60 such clumps were located randomly throughout each plot. These clumps were then re-checked each week, and the number of missing berries were noted. From these data, the percentage of berries lost each week was determined for each plot. A wettable powder formulation of both methiocarb and trimethacarb was applied at a rate of 3.0 kg ha -1 using a Solo backpack sprayer. Proportionately lower rates were used in fields containing immature plants so that all berries received an approximately equal coverage. Equal amounts of methiocarb and trimethacarb were always used, however, in each individual field. To test the efficacy of these repellents, the plot at the Station's farm was divided in half. The plots at Rose's Berry farm were divided into thirds. Bird damage in each of these sections was first measured during a 1-week pretreatment period. Thereafter, one of the sections in each field was randomly selected and treated with one of the repellents. Two weeks later, another section in each field was sprayed with the other repellent. The different repellent applications were staggered in order to monitor any change in bird damage both in the treated and untreated sections. This arrangement permitted a determination of any carryover effect to nearby untreated fruit by using data from Rose's Berry Farm. Data from the Station's farm were excluded from this analysis because of the unavailability of an untreated section. For most analyses there were 9 replicates, but for the comparison involving the nearby untreated sections, there were 7. Bird damage in the treated sections and in the nearby untreated sections were compared to t h a t occurring in these same sections during the pre-
385
treatment period using a Student's t-test to test for statistically significant (P < 0.05) differences. The t-test was also used to determine if there were any statistically significant differences between the t w o repellents in reducing berry loss in the treated sections. RESULTS
In the plots treated with trimethacarb, berry loss decreased from 45% in the pre-test period to 21% during the first week after treatment. This decrease (52%) was statistically significant (Table I). During this same period of time, the percentage of berry loss in the methiocarb plots significantly decreased by 25% (from 40% berry loss in the pre-test period to 30% after treatment). During the second week of the treatment period, berry loss was 34 and 33% in the methiocarb and trimethacarb plots, respectively. This represented a non-significant reduction in berry loss of 13% in the methiocarb plots and 27% in the trimethacarb plots compared to damage in these same plots during the pre-test period. While trimethacarb was slightly more effective than methiocarb in reducing berry loss, these differences between the t w o repellents were not statistically significant in either the first (t = 0.85) or second week (t = 0.56) following their application. TABLE I Berry loss before and after application of methiocarb or trimethacarb to the treated plots Berry loss (%)
t-test (vs. pre-treatment)
Pre-test Period
Treatment period
Treatment period
Week 1
Week 2
Week 1
Week 2
Methiocarb test Treated plots Untreated plots
39.7 34.4
29.7 43.2
34.2 43.6
2.47* 0.99
1.85 2.67*
Trimethacarb test Treated plots U n t r e a t e d plots
44.9 45.1
21.4 37.6
32.8 41.0
4.20** 1.14
1.60 0.57
*(P < 0.05). **(P < 0.01).
The protection afforded by either of these repellents was limited to the treated plots (Table I). In neither case did berry loss significantly decrease in the nearby untreated plots following repellent application to the other plots (t =0.99 and 1.14 for methiocarb and trimethacarb, respectively). In fact, berry loss increased slightly in the untreated plots following the application of methiocarb.
386 DISCUSSION B o t h m e t h i o c a r b (Rogers, 1 9 7 4 ) a n d t r i m e t h a c a r b ( G u s t a v s o n a n d Basche, 1 9 8 3 ) a p p a r e n t l y f u n c t i o n b y establishing in birds a c o n d i t i o n e d aversion t o t r e a t e d f o o d . In m y e x p e r i m e n t s , b o t h c h e m i c a l s significantly r e d u c e d bird d a m a g e t o t r e a t e d b l u e b e r r i e s f o r a 1-week p e r i o d f o l l o w i n g a p p l i c a t i o n . Trim e t h a c a r b was slightly m o r e e f f e c t i v e t h a n m e t h i o c a r b in r e d u c i n g b e r r y loss d u r i n g b o t h p o s t - t r e a t m e n t weeks. I n no case, h o w e v e r , w e r e t h e s e diff e r e n c e s b e t w e e n t h e t w o r e p e l l e n t s statistically significant. B o t h c h e m i c a l s a p p e a r effective in r e d u c i n g bird d a m a g e t o blueberries. C o n s e q u e n t l y , t h e relative c o s t o f t h e s e chemicals will p r o b a b l y have a m a j o r i n f l u e n c e o n w h i c h o n e f a r m e r s d e c i d e t o use. C u r r e n t l y , m e t h i o c a r b costs $ 4 4 kg -1 in t h e U.S., while t h e m a r k e t price o f t r i m e t h a c a r b is u n k n o w n . A l t h o u g h b o t h c h e m i c a l s p r o t e c t e d berries in t h e t r e a t e d plots, n e i t h e r red u c e d d a m a g e significantly in t h e n e a r b y u n t r e a t e d plots. A p p a r e n t l y , birds w e r e able t o d i s c r i m i n a t e b e t w e e n t r e a t e d and u n t r e a t e d berries, p e r h a p s b y using subtle t a s t e or visual cues. T h e y a p p e a r e d t o h a v e a v e r t e d n o t f r o m t h e t a s t e or sight o f b l u e b e r r i e s t h e m s e l v e s , b u t o n l y f r o m t r e a t e d berries. This d i s c r i m i n a t i o n , u n f o r t u n a t e l y , allows t h e birds to search o u t a n d forage in o t h e r u n t r e a t e d b l u e b e r r y fields and t o r e t u r n t o s p r a y e d field a f t e r t h e rep e l l e n t has w a s h e d o f f ( C o n o v e r , 1 9 8 4 ) . ACKNOWLEDGEMENTS I thank the owners and employees of Rose's Berry Farm for generously allowing m e to use s o m e o f t h e i r b l u e b e r r y fields f o r m y e x p e r i m e n t s . G.S. K a n i a a n d B.E. Y o u n g h e l p e d collect t h e data. D.E. A y l o r , D.O. C o n o v e r a n d P.A. H a l b e r t h e l p e d i m p r o v e earlier versions o f this m a n u s c r i p t . REFERENCES Conover, M.R., 1981. Evaluation of behavioral techniques to reduce wildlife damage. In: L. Nelson, Jr. and J.M. Peek (Editors), Proc. Wildl.-Livestock Relationships Syrup., Forest, Wildl. Range Exp. Stn., Moscow, ID, pp. 332--344. Conover, M.R., 1982. Behavioral techniques to reduce bird damage to blueberries: methiocarb and a hawk--kite predator model. Wildl. Soc. Bull., 10: 211--216. Conover, M.R., 1984. Response of birds to different types of food repellents. J. Appl. Ecol., in press. Guarino, J.L., Stone, C.P. and Shake, W.F., 1973. A low-level treatment of an avian repellent, methiocarb, on ripening cherries. In: H.J. Cones, Jr. and W.B. Jackson (Editors), Proc. Bird Control Seminar 6, Bowling Green, OH, pp. 24--27. Guarino, J.L., Shake, W.F. and Schafer, E.W., Jr., 1974. Reducing bird damage to ripening cherries with methiocarb. J. Wildl. Manage., 38: 338--342. Gustavson, C.R. and Basche, L.A., 1983. Landrin- and thiabendazole-based conditioned taste aversions in domestic ducks. Appl. Anita. Ethol., 9: 379--380. Nicolaus, L.K., Cassel, J.F., Carlson, R.B. and Gustavson, C.R., 1983. Taste-aversion conditioning of crows to control predation on eggs. Science, 220: 212--214. Rogers, J.G., Jr., 1974. Responses of caged Red-winged Blackbirds to two types of repellents. J. Wildl. Manage., 38: 418--423. Stone, C.P., Shake, W.F. and Langowski, D.J., 1974. Reducing bird damage to highbush blueberries with a carbamate repellent. Wildl. Soc. Bul.., 2: 135--139.
383
USING CONDITIONED FOOD AVERSIONS TO PROTECT BLUEBERRIES FROM BIRDS: COMPARISON OF TWO CARBAMATE REPELLENTS
MICHAEL R. CONOVER Department of Ecology and Climatology, The Connecticut Agricultural Experiment Station, Box 1106, New Haven, CT 06504 (U.S.A.) (Accepted for publication 7 June 1984)
ABSTRACT Conover, M.R., 1985. Using conditioned food aversions to protect blueberries from birds: comparison of two carbamate repellents. AppL Anim. Behav. Sci., 13: 383--386. This study compared the effectiveness of two carbamate repellents (trimethacarb and methiocarb) in protecting blueberry fields from fruit loss caused by birds (primarily Northern Mockingbirds, European Starlings and Northern Orioles). Methiocarb and trimethacarb reduced berry loss significantly in the treated plots by 25 and 52%, respectively, during the first week after application. Differences between the two repellents in effectiviness, however, were not statistically significant. Moreover, neither repellent reduced berry loss significantly in adjacent untreated plots. These results indicate that both repellants caused birds to avert only from treated berries, and not from the taste or sight of blueberries themselves.
INTRODUCTION C o n d i t i o n e d f o o d aversions o f f e r ranchers, f a r m e r s a n d wildlife m a n a g e r s a n e w t o o l f o r alleviating specific p r o b l e m s caused b y animals ( C o n o v e r , 1 9 8 1 ) . One o f t h e m o s t successful uses o f aversive c o n d i t i o n i n g has b e e n t h e alleviation o f bird d a m a g e t o small fruit b y using m e t h i o c a r b ( 3 - 5 - d i m e t h y l 4-methylthiophenol methylcarbamate), produced by the Mobay Chemical C o r p o r a t i o n as Mesurol. M e t h i o c a r b has r e d u c e d bird d a m a g e t o b o t h ripening b l u e b e r r i e s ( S t o n e et al., 1 9 7 4 ; C o n o v e r , 1 9 8 2 ) a n d cherries ( G u a r i n o et al., 1 9 7 3 , 1 9 7 4 ) , a n d has gained clearance for such use b y t h e U.S. Envir o n m e n t a l P r o t e c t i o n A g e n c y . A l t h o u g h e f f e c t i v e in r e d u c i n g bird d a m a g e t o t h e s e fruit, m e t h i o c a r b has t w o d r a w b a c k s : (1) its e x p e n s e {costing a b o u t $ 1 3 2 h a -1 w h e n applied at an e f f e c t i v e r a t e o f 3.0 kg h a - l ) ; (2) its d e t e c t a b i l i t y o n s p r a y e d fruit, causing birds t o a v e r t f r o m its t a s t e r a t h e r t h a n f r o m t h e f r u i t itself ( C o n o v e r , 1 9 8 2 ) . H e n c e , birds can r e t u r n t o a s p r a y e d o r c h a r d a f t e r t h e r e p e l l e n t has w a s h e d o f f , or cause d a m a g e in n e a r b y u n t r e a t e d orchards (Conover, 1984). T h e goal o f this s t u d y was t o t e s t a n d c o m p a r e t h e ability o f m e t h i o c a r b 0168-1591/85/$03.30
© 1985 Elsevier Science Publishers B.V.
384 and a new carbamate repellent, trimethacarb (UC 27867), to reduce bird damage to both treated and nearby untreated plots of blueberries. Trimethacarb, made by Union Carbide, contains a mixture of 3,4,5- and 2,3,5-trimethylphenyl carbamate. It already has been used successfully to establish conditioned taste aversions in domestic ducks (Gustavson and Basche, 1983) and American Crows, Corvus brachyrhynchos (Nicolaus et al., 1983). METHODS These experiments were conducted during 1982 and 1983 at both the Connecticut Agricultural Experiment Station's farm in Hamden, where these repellents were tested on a 0.05-ha blueberry planting consisting of 7 highbush blueberry varieties (Concord, Pemberton, Weymouth, Atlantic, Jersey, Dixie and Burlington), and at Rose's Berry Farm in Glastonbury, CT, where five 0.4--1.0-ha field were used. Each field consisted of one of the following varieties: Berkley; Blue Crop; Bluetta; Darrow; Patriot. The major bird pests in these blueberry fields (Conover, 1982) were Northern Mockingbirds (Mimus polyglottos), Northern Orioles (Icterus galbula), American Robins (Turdus migratorius) and European Starlings (Sturnus vulgaris). Bird damage was monitored in each plot by marking clumps of 10 berries with small strings to facilitate later identification. At least 60 such clumps were located randomly throughout each plot. These clumps were then re-checked each week, and the number of missing berries were noted. From these data, the percentage of berries lost each week was determined for each plot. A wettable powder formulation of both methiocarb and trimethacarb was applied at a rate of 3.0 kg ha -1 using a Solo backpack sprayer. Proportionately lower rates were used in fields containing immature plants so that all berries received an approximately equal coverage. Equal amounts of methiocarb and trimethacarb were always used, however, in each individual field. To test the efficacy of these repellents, the plot at the Station's farm was divided in half. The plots at Rose's Berry farm were divided into thirds. Bird damage in each of these sections was first measured during a 1-week pretreatment period. Thereafter, one of the sections in each field was randomly selected and treated with one of the repellents. Two weeks later, another section in each field was sprayed with the other repellent. The different repellent applications were staggered in order to monitor any change in bird damage both in the treated and untreated sections. This arrangement permitted a determination of any carryover effect to nearby untreated fruit by using data from Rose's Berry Farm. Data from the Station's farm were excluded from this analysis because of the unavailability of an untreated section. For most analyses there were 9 replicates, but for the comparison involving the nearby untreated sections, there were 7. Bird damage in the treated sections and in the nearby untreated sections were compared to t h a t occurring in these same sections during the pre-
385
treatment period using a Student's t-test to test for statistically significant (P < 0.05) differences. The t-test was also used to determine if there were any statistically significant differences between the t w o repellents in reducing berry loss in the treated sections. RESULTS
In the plots treated with trimethacarb, berry loss decreased from 45% in the pre-test period to 21% during the first week after treatment. This decrease (52%) was statistically significant (Table I). During this same period of time, the percentage of berry loss in the methiocarb plots significantly decreased by 25% (from 40% berry loss in the pre-test period to 30% after treatment). During the second week of the treatment period, berry loss was 34 and 33% in the methiocarb and trimethacarb plots, respectively. This represented a non-significant reduction in berry loss of 13% in the methiocarb plots and 27% in the trimethacarb plots compared to damage in these same plots during the pre-test period. While trimethacarb was slightly more effective than methiocarb in reducing berry loss, these differences between the t w o repellents were not statistically significant in either the first (t = 0.85) or second week (t = 0.56) following their application. TABLE I Berry loss before and after application of methiocarb or trimethacarb to the treated plots Berry loss (%)
t-test (vs. pre-treatment)
Pre-test Period
Treatment period
Treatment period
Week 1
Week 2
Week 1
Week 2
Methiocarb test Treated plots Untreated plots
39.7 34.4
29.7 43.2
34.2 43.6
2.47* 0.99
1.85 2.67*
Trimethacarb test Treated plots U n t r e a t e d plots
44.9 45.1
21.4 37.6
32.8 41.0
4.20** 1.14
1.60 0.57
*(P < 0.05). **(P < 0.01).
The protection afforded by either of these repellents was limited to the treated plots (Table I). In neither case did berry loss significantly decrease in the nearby untreated plots following repellent application to the other plots (t =0.99 and 1.14 for methiocarb and trimethacarb, respectively). In fact, berry loss increased slightly in the untreated plots following the application of methiocarb.
386 DISCUSSION B o t h m e t h i o c a r b (Rogers, 1 9 7 4 ) a n d t r i m e t h a c a r b ( G u s t a v s o n a n d Basche, 1 9 8 3 ) a p p a r e n t l y f u n c t i o n b y establishing in birds a c o n d i t i o n e d aversion t o t r e a t e d f o o d . In m y e x p e r i m e n t s , b o t h c h e m i c a l s significantly r e d u c e d bird d a m a g e t o t r e a t e d b l u e b e r r i e s f o r a 1-week p e r i o d f o l l o w i n g a p p l i c a t i o n . Trim e t h a c a r b was slightly m o r e e f f e c t i v e t h a n m e t h i o c a r b in r e d u c i n g b e r r y loss d u r i n g b o t h p o s t - t r e a t m e n t weeks. I n no case, h o w e v e r , w e r e t h e s e diff e r e n c e s b e t w e e n t h e t w o r e p e l l e n t s statistically significant. B o t h c h e m i c a l s a p p e a r effective in r e d u c i n g bird d a m a g e t o blueberries. C o n s e q u e n t l y , t h e relative c o s t o f t h e s e chemicals will p r o b a b l y have a m a j o r i n f l u e n c e o n w h i c h o n e f a r m e r s d e c i d e t o use. C u r r e n t l y , m e t h i o c a r b costs $ 4 4 kg -1 in t h e U.S., while t h e m a r k e t price o f t r i m e t h a c a r b is u n k n o w n . A l t h o u g h b o t h c h e m i c a l s p r o t e c t e d berries in t h e t r e a t e d plots, n e i t h e r red u c e d d a m a g e significantly in t h e n e a r b y u n t r e a t e d plots. A p p a r e n t l y , birds w e r e able t o d i s c r i m i n a t e b e t w e e n t r e a t e d and u n t r e a t e d berries, p e r h a p s b y using subtle t a s t e or visual cues. T h e y a p p e a r e d t o h a v e a v e r t e d n o t f r o m t h e t a s t e or sight o f b l u e b e r r i e s t h e m s e l v e s , b u t o n l y f r o m t r e a t e d berries. This d i s c r i m i n a t i o n , u n f o r t u n a t e l y , allows t h e birds to search o u t a n d forage in o t h e r u n t r e a t e d b l u e b e r r y fields and t o r e t u r n t o s p r a y e d field a f t e r t h e rep e l l e n t has w a s h e d o f f ( C o n o v e r , 1 9 8 4 ) . ACKNOWLEDGEMENTS I thank the owners and employees of Rose's Berry Farm for generously allowing m e to use s o m e o f t h e i r b l u e b e r r y fields f o r m y e x p e r i m e n t s . G.S. K a n i a a n d B.E. Y o u n g h e l p e d collect t h e data. D.E. A y l o r , D.O. C o n o v e r a n d P.A. H a l b e r t h e l p e d i m p r o v e earlier versions o f this m a n u s c r i p t . REFERENCES Conover, M.R., 1981. Evaluation of behavioral techniques to reduce wildlife damage. In: L. Nelson, Jr. and J.M. Peek (Editors), Proc. Wildl.-Livestock Relationships Syrup., Forest, Wildl. Range Exp. Stn., Moscow, ID, pp. 332--344. Conover, M.R., 1982. Behavioral techniques to reduce bird damage to blueberries: methiocarb and a hawk--kite predator model. Wildl. Soc. Bull., 10: 211--216. Conover, M.R., 1984. Response of birds to different types of food repellents. J. Appl. Ecol., in press. Guarino, J.L., Stone, C.P. and Shake, W.F., 1973. A low-level treatment of an avian repellent, methiocarb, on ripening cherries. In: H.J. Cones, Jr. and W.B. Jackson (Editors), Proc. Bird Control Seminar 6, Bowling Green, OH, pp. 24--27. Guarino, J.L., Shake, W.F. and Schafer, E.W., Jr., 1974. Reducing bird damage to ripening cherries with methiocarb. J. Wildl. Manage., 38: 338--342. Gustavson, C.R. and Basche, L.A., 1983. Landrin- and thiabendazole-based conditioned taste aversions in domestic ducks. Appl. Anita. Ethol., 9: 379--380. Nicolaus, L.K., Cassel, J.F., Carlson, R.B. and Gustavson, C.R., 1983. Taste-aversion conditioning of crows to control predation on eggs. Science, 220: 212--214. Rogers, J.G., Jr., 1974. Responses of caged Red-winged Blackbirds to two types of repellents. J. Wildl. Manage., 38: 418--423. Stone, C.P., Shake, W.F. and Langowski, D.J., 1974. Reducing bird damage to highbush blueberries with a carbamate repellent. Wildl. Soc. Bul.., 2: 135--139.