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Anti-predator behavior in birds: Reactions to raptor calls

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Title:
Anti-predator behavior in birds: Reactions to raptor calls
Translated Title:
Comportamiento anti-depredador en las aves: Las reacciones a las llamadas de las aves rapaces
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Elahi, Robin
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Birds--Behavior ( lcsh )
Aves--Comportamiento ( lcsh )
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
CIEE Fall 2000
CIEE Otoño 2000
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Abstract:
Birds display a number of defense mechanisms against their predators, including camouflage, mobbing, fleeing, and aggregational behavior. I studied the responses of 32 bird species to songbird and raptor calls to see if birds displayed anti-predator behavior in response to raptor calls in comparison with songbird calls. One focus of my study was avian defensive strategies, namely flocking and concealment, so observations took into consideration different conditions: whether the bird was solitary or in a group, and whether it was exposed or hidden in vegetation. A previous study showed that crows could distinguish between raptor calls of their predators and non-predators, so I examined if birds specifically recognized resident raptors, or if they had a general response to resident and non-resident raptor calls. I also attempted to correlate bird size with reaction, specifically to see if smaller birds flew away more often than larger birds due to a greater perceived threat. For each bird or group of birds. I played a songbird call, followed by a raptor call, and timed the raptor call to see how long the bird stayed till it flew away. Birds flew away 27% of the time in response to raptor calls, and only 3% of the time to songbird calls (X² = 16.11, df = 1, n = 26). Birds did not distinguish among resident and non-resident raptor calls, and had nearly equal flight frequencies (X² = 0.48, df =3, n=40). Trends showed that solitary and exposed birds tended to fly more often than birds in groups and hidden birds. Bird size was not a reliable indicator of reactions, although a trend demonstrate that average bird size was larger for flight reactions, than for no reactions or look reactions (One-way ANOVA, p = 0.1314). These results suggest that birds use the antipredator strategies of flocking and concealment, however, further research should be done on raptor call recognition on a single genus or species of birds to determine if raptor calls recognition is specific on a lower taxonomic level as previous studies have suggested. ( , )
Abstract:
Los pájaros exhiben una variedad de mecanismos defensivos contra sus predadores, incluyendo camuflaje, ataque, huir o hacer grupos. Estudie las reacciones de 32 especies de pájaros al sonar cantos de aves canoras y aves de rapiña, para ver si los pájaros exhibieron un comportamiento anti-predador. El enfoque de mi estudio fueron las estrategias de las aves, específicamente en grupos y escondidos, por eso en las observaciones se tomaron en consideración si los pájaros estuvieron en grupo o solitarios o si estuvieron escondidos en la vegetación o no. Un estudio anterior demostró que los cuervos distinguieron entre las llamadas de rapaces, por eso examine si los pájaros específicamente distinguieron entre llamadas de aves de rapiña residente y no-residente, o si tuvieron una respuesta general a todas las llamadas de ave de rapiña. También trate de tomar en cuenta el tamaño del pájaro con la reacción, específicamente si los pájaros pequeños volaron más que los pájaros grandes. Para cada pájaro o grupo de pájaros, soné una llamada de ave canora e inmediatamente después una llamada de ave de rapiña y conté el tiempo que le tomo al pájaro volar. Los pájaros volaron en 27% del tiempo en respuesta a las llamadas de rapiña y solamente 3% del tiempo a las llamadas de aves canoras (X² = 16.11, df = 1, n = 26). Los pájaros no distinguieron entre las aves de rapiñas residentes y no-residentes y tuvieron casi la misma frecuencia de vuelo (X² = 0.48, df = 3, n = 40. Las tendencias mostraron que pájaros solitarios y expuestos volaron más que las aves en grupo o escondidas. El tamaño del pájaro no fue un indicador para las reacciones pero una tendencia mostro que el tamaño fue un factor para cuando volaron, que para cuando no lo hicieron o para cuando solo miraron (One-way ANOVA, p= 0.1314). Estos resultados sugieren que los pájaros usan estrategias anti-predador, pero se debe estudiar más el reconocimiento de una especie de pájaro de cómo distingue las llamadas de aves de rapiña para determinar si el reconocimiento es específico en especies como mostraron los estudios anteriores.
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Student affiliation: Department of Biology, Northeastern University

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Anti predator behavior in Birds: Reactions to Raptor Calls Robin Elahi Department of Biology, Northeastern University _____________________________________________________________________________________ ABSTRACT Birds display a number of defense mechanism s against their predators, including camouflage, mobbing, fleeing, and aggregational behavior. I studied the responses of 32 bird species to songbird and raptor calls to see if birds displayed anti predator behavior in response to raptor calls in compariso n with songbird calls. One focus of my study was avian defensive strategies, namely flocking and concealment, so observations took into consideration different conditions: whether the bird was solitary or in a group, and whether it was exposed or hidden in vegetation. A previous study showed that crows could distinguish between raptor calls of their predators and non predators, so I examined if birds specifically recognized resident raptors, or if they had a general response to resident and non resident rap tor calls. I also attempted to correlate bird size with reaction, specifically to see if smaller birds flew away more often than larger birds due to a greater perceived threat. For each bird or group of birds. I played a songbird call, followed by a raptor call, and timed the raptor call to see how long the bird stayed till it flew away. Birds flew away 27% of the time in response to raptor calls, and only 3% of the time to songbird calls X = 16.11, df = 1, n = 26. Birds did not distinguish among residen t and non resident raptor calls, and had nearly equal flight frequencies X = 0.48, df =3, n=40. Trends showed that solitary and exposed birds tended to fly more often than birds in groups and hidden birds. Bird size was not a reliable indicator of react ions, although a trend demonstrate that average bird size was larger for flight reactions, than for no reactions or look reactions One way ANOVA, p = 0.1314. These results suggest that birds use the anti predator strategies of flocking and concealment, h owever, further research should be done on raptor call recognition on a single genus or species of birds to determine if raptor calls recognition is specific on a lower taxonomic level as previous studies have suggested. RESUMEN Los pjaros exhiben una var iedad de mecanismos defensivos contra sus predadores, incluyendo camuflaje, ataque, huir o hacer grupos. Estudie las reacciones de 32 especies de pjaros al sonar cantos de aves canoras y aves de rapia, para ver si los pjaros exhibieron un comportamiento anti predador. El enfoque de mi estudio fueron las estrategias de las aves, especficamente en grupos y escondidos, por eso en las observaciones se tomaron en consideracin si los pjaros estuvieron en grupo o solitarios o si estuvieron escondidos en la v egetacin o no. Un estudio anterior demostr que los cuervos distinguieron entre las llamadas de rapaces, por eso examine si los pjaros especficamente distinguieron entre llamadas de aves de rapia residente y no residente, o si tuvieron una respuesta ge neral a todas las llamadas de ave de rapia. Tambin trate de tomar en cuenta el tamao del pjaro con la reaccin, especficamente si los pjaros pequeos volaron ms que los pjaros grandes. Para cada pjaro o grupo de pjaros, son una

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llamada de ave ca nora e inmediatamente despus una llamada de ave de rapia y cont el tiempo que le tomo al pjaro volar. Los pjaros volaron en 27% del tiempo en respuesta a las llamadas de rapia y solamente 3% del tiempo a las llamadas de aves canoras X = 16.11, df = 1, n = 26. Los pjaros no distinguieron entre las aves de rapias residentes y no residentes y tuvieron casi la misma frecuencia de vuelo X = 0.48, df = 3, n = 40. Las tendencias mostraron que pjaros solitarios y expuestos volaron ms que las aves en grupo o escondidas. El tamao del pjaro no fue un indicador para las reacciones pero una tendencia mostro que el tamao fue un factor para cuando volaron, que para cuando no lo hicieron o para cuando solo miraron One way ANOVA, p= 0.1314. Estos resultad os sugieren que los pjaros usan estrategias anti predador, pero se debe estudiar ms el reconocimiento de una especie de pjaro de cmo distingue las llamadas de aves de rapia para determinar si el reconocimiento es especfico en especies como mostraron los estudios anteriores. INTRODUCTION Predators confer Strong selective pressure on their prey, resulting in varied defense mechanisms. Animals have developed two basic types of strategies to prevent predation € anti detection and anti capture Alcock 1984 Anti detection strategies rely on remaining invisible to the predator, through cryptic coloration and background matching. This is seen in many different taxa, such as lizards, insects and birds. Anti capture strategies are behaviors displayed after the prey has been spotted by their predator, such as flash colors, misdirecting an attack, chemical repellants, Batesian mimicry, fleeing and fighting back Alcock 1984. Birds avoid predation by raptors using both anti detection and anti capture strategies. Many birds, such as Amazonia parrots, blend in with their environment and are very difficult to see, which serves as an anti detection strategy. Once a raptor has spotted its prey, anti capture strategies include diving into thick bushes or water, and sim ply fleeing and dodging. These actions are often accompanied by alarm calls Perrins 1979. Birds have also evolved anti capture behaviors such as mobbing and aggregational behavior. For example, European kestrels mobbed by foraging birds flew significantl y farther from foraging areas, and thus supports the assumption that mobbing decreases predatory efficiency, mainly by driving the predator from the vicinity Pettifor 1990. Aggregational behavior has been shown to be an effective defense against predato rs in numerous studies on leks, foraging flocks, and escape tactics Buchanan et al. 1988, Caldwell 1986, Glodman 1980, Trail 1998. Flocks provide increased vigilance because of the greater number of eyes to spot predators. As a result, individuals can in crease the time they spend foraging since they spend less time watching for danger. Lima 1998 has shown that solitary birds that are not overtly vigilant i.e. birds that are feeding are more vulnerable to predator attack. Additionally, the selfish herd hypothesis states that an individuals chances of being eaten decrease when they join a group, simply because of probability Terborgh 1989. The dilution effect explains that groups will likely satiate their predators, and again, the individuals chances of survival increase due to probability, since only a few prey will be taken Alcock 1984. Since aggregational behavior and concealment are key defense mechanisms for birds, I tried to measure the effects of these variables on the reaction of birds in r esponse

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to songbird and raptor calls. The reactions to songbird calls provide a control to compare the reactions of raptor calls. Based on avian anti predator strategies, solitary birds should fly away more often and more readily than birds in groups. Like wise, exposed birds should fly away more often than hidden birds. I am also interested in whether birds respond specifically to the calls of resident raptors, or whether they have a general raptor call response. Western American Crows Corvus brachyrhynch os hesperis not only distinguish between raptor and non raptor calls, they can also distinguish the calls of Red Shouldered Hawks Buteo lineatus a major predator, from the Madagascar Harrier Hawk Gymnogenys radiatus that has a spectrally similar call Hauser and Caffrey 1994. Therefore, it appears birds will distinguish between songbirds and raptors, and that at least some birds will recognize the calls of raptors that are common in the area, and as a result, fly more often and more readily from thos e calls. The Great Blawk Hawk Buteogallus anthracinus and the Collared Forest Falcon Micrastur semitorquatus were chosen as representative of the San Luis area, while the Semiplumbeous Hawk Leucopternis seminplumbea and the Slaty Backed Forest Falcon Micrastur mirandollei frequent other areas, mainly the Caribbean slope Mauricio Ramirez, Manuel Leitn, pers. comm.; Fogden 1993, Stiles and Skutch 1989. As a last inquiry, I wished to examine the relationship between bird size and reaction. Only lar ger birds were found to mob kestrels because it seemed unlikely that the kestrels posed a great threat to them Pettifor 1990. I hypothesize that smaller birds will fly more often than larger birds, because of the greater perceived threat. MATERIALS AND METHODS Calls were played to 87 birds of 32 different species in San Luis Arriba and Invu, Costa Rica, located on the Pacific slope of the Tilarn mountain range at 1100m elevation between October 25 and November 14, 2000. The Holdridge life zone is premon tane wet forest Holdridge 1967, Haber et al. 2000. Data were collected from 5:30 € 8:30 AM and 3:00 € 5:00 PM, along roads and trails in pasture, secondary growth forest and gardens. I walked trails, stopping to make observations at certain points for d urations of five to twenty minutes depending on bird activity. Once a bird was perched and identified using binoculars, I played a call sequence once, at medium to high volume depending on distance from the observed bird i.e. volume increased with increas ed distance with a portable cassette player, pointed straight up in the air. The distance ranged from two meters to 25m. There were four different call sequences, each consisting of a songbird call, immediately followed by a raptor call, as follows time in seconds is noted in parentheses: Sequence 1: Tropical Pewee 39s, Great Blawk Hawk 39s Sequence 2: Buff Throated Wood Creeper 44s, Semiplumbeous Hawk 35s Sequence 3: Striped Breasted Wren 45s, Collared Forest Falcon 54s Sequence 4: Yellow F aced Grassquit 29s, Slaty Backed Forest Falcon 33s

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The specificity of bird responses to native raptors was tested by sequences one and three, and to non native raptors by two and four, as explained above. At the start of the raptor call I started timin g to see how long the bird stayed. I categorized three reactions to the bird calls € ‚Noneƒ, ‚Lookƒ, and ‚Flyƒ. ‚Noneƒ indicates the bird did nothing by the time call ended. ‚Lookƒ meant the bird stopped his current activity e.g. singing, pecking and lo oked around, and ‚Flyƒ meant the bird flew away. Each call sequence was played only once. If the bird was by itself, it was ‚Solitaryƒ, and if it was with at least one other bird only one group of birds I observed was made up of more than one species tha t was noted as a ‚Groupƒ. Groups that displayed a ‚flyƒ reaction had at least half of their birds fly away. Whether the bird was ‚Exposedƒ or ‚Hiddenƒ was also noted € ‚Exposedƒ meant that the bird was in clear view; if the bird was at least partly surroun ded by vegetation it was defined as ‚Hiddenƒ. The birds I chose for songbird calls are in the order Passeriformes. This order is characterized by the morphology of the syrinx the organ of sound production Janzen 1983. The four chosen songbirds range f rom 10 to 22 cm in length, and eat a variety of seeds, fruits and insects. The raptors whose calls I used range from 38 to 66cm; they eat birds and eggs Stiles and Skutch 1989. The raptors are in the order Falconiformes, which includes hawks, eagles and falcons. They are diurnal hunters who rely mainly on sight; they have no sense of smell Perrins 1979. These birds of prey are vocal when demonstrating territoriality, and when performing courtship rituals, as most other birds Perrins 1979. Skutch and Stiles 1989 aided in identification, and reported bird size in length cm. Chi square tests were used to determine the significance of bird reactions to the different calls songbird vs. raptor, raptor vs. raptor, and under the four different conditi ons solitary vs. group, exposed vs. hidden. One way ANOVA tests were used to relate flight times with the different raptor calls and the different conditions. One way ANOVA tests were also run between bird size and reaction. RESULTS Eighty seven call s equences were played to birds; three of the birds flew after hearing the songbird calls, and thus 87 birds listened to songbird calls and 84 birds listened to raptor calls. There were significant differences between the songbird and raptor calls in all thr ee reactions, ‚Noneƒ, ‚Lookƒ, and ‚Flyƒ X„ = 30.78, df = 1, n = 99; X„ = 26.57, df = 1, n = 46; X = 16.11, df = 1, n = 26, respectively; Figure 1. Differences in reaction were strikingly clear, for example, songbird reactions elicited no reaction 90% of the time, while raptor reactions elicited no reaction only 25% of the time. All four raptor calls were played to 21 birds each. The number of flight reactions were almost equal for all four calls five for both the Great Blawk Hawk and Collared Forest Falcon, six for the Semiplumbeous Hawk, and seven for the Slaty Backed Forest Falcon. There was no significant differences in any of the reactions between the four raptor calls X = 1.29, df = 3, n=21, X = 1.0, df = 3, n = 40, X = 0.48, df = 3, n=40;

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‚ Noneƒ, ‚Lookƒ, ‚Flyƒ, respectively; Figure 2. For those birds that flew off, there was no significant difference in time One way ANOVA, p = .3019; Figure 3. Raptor calls were played to 51 solitary birds, and 33 groups of birds. Flycatchers, such as Tropical Pewees Contopus cinereus Great Kiskadees Pitangus sulphuratus and the Myiozetetes flycatchers tended to be solitary, while Yellow Throated Euphonias Euphonia hirundinacea Groove Billed Anis Crotophaga sulcirostris and White Fronted Par rots Amazona albifrons were always observed to be in groups. 35% of solitary birds flew, while only 15% of the groups flew Figure 4 X = 2.98, df = 1, n = 23. For those that flew, that average time for solitary birds was 19.86 seconds, and for groups was 24.40 seconds One way ANOVA, p = 0.454. No reaction was observed 20% of the time for solitary birds, and 33% of the time for groups X = 1.51, df = 1, n =22. ‚Lookƒ reactions were observed 45% and 52% of the time for solitary birds and groups, res pectively X = 0.17, df =1, n=40. Raptor calls were played to 66 exposed and 18 hidden birds and groups Figure 5. 32% and 11% of the subjects flew, respectively X = 2.20, df = 1, n = 23. The average flight time for exposed and hidden birds that fle w was 21.69 and 12 seconds, respectively One way ANOVA, p = 0.271. No reaction was observed 21% of the time for exposed birds, and 39% of the time for hidden birds X„ = 1.77, df = 1, n = 21. ‚Lookƒ reactions were observed 45% and 52% of the time for ex posed and hidden birds, respectively X = 1.39, df = 1, n = 40. A significant X value of 17.1 was calculated for a table between the solitary and group conditions versus the exposed and hidden conditions Table 1. The exposed row contained 21 flight r eactions, and the solitary column contained 18 flight reactions, while the hidden and group rows contained only two and five flight reactions respectively. Birds ranged from 10 cm House wren to 101 cm Great Egret. When all the reactions to raptor call s were compared by bird size, there was no significant difference One way ANOVA, p = 0.846. To eliminate any bias from the different conditions e.g. solitary vs. group, the test was run only for solitary and exposed birds, since that was largest sample size n= 37; One way ANOVA, p = 0.131. The average bird size for fly reactions under these specific conditions was 21.47cm, while the average bird size for look and no reactions were 16.84 and 16.67, respectively. The difference lay between fly and loo k One way ANOVA, p = 0.064, and between fly and none One way ANOVA, p = 0.149 reactions. DISCUSSION Birds showed significant differences for all reactions with songbird calls and raptor calls Figure 1. Ninety percent of the time, subjects showed no reaction to the songbird calls, compared with only 25% that showed no reaction to the raptor calls. The songbird calls thus served well as a control, demonstrating that the birds were not scared of me, and were not just reacting to sounds coming out of my tape player. Similarly, since birds only flew away 3% of the time to songbird calls, and 27% of the time to raptor calls, it suggests that birds did indeed perceive a difference between the two types of calls. These

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results support the previous study in w hich Western American Crows reacted to predator calls, but not to non predators Hauser and Caffrey 1994. The resident and non resident raptor calls elicited nearly equal flight reactions Figure 2. The times for flight were also not significantly diffe rent Figure 3. Thus, it seems that birds have general raptor call recognition, instead of only recognizing specific raptors. This makes sense evolutionarily, because those birds who react to strange raptor calls would have higher fitness than those birds who only responded to familiar raptor calls. My results are different from Hausers and Caffreys 1994; they found that crows fly away only from their actual predator calls. The discrepancy here may be explained by the fact that I tested any species of bird I saw, while they studied one specific species, and they knew the actual predators from past research. The raptors whose calls I used are in the area, and they eat other birds and eggs in general, but it is unknown if they specifically search for prey of a certain genus or guild in the San Luis area. The birds that tended to be solitary and in groups as mentioned above confirmed the habits described in Skutch and Stiles 1989. The trend towards higher flight frequency and faster flight times among ma ny species of solitary birds compared with birds in groups supports the hypothesis that solitary birds are more vulnerable to predation Buchanan et al. 1988, Lima 1998. Since solitary birds are more vulnerable, an d spend more time assessing their surroun dings Goldman 1980, it seems likely and more adaptive that they would flee more often. Being in groups is a safety measure due to increased vigilance, the selfish herd hypothesis, and the dilution effect Alcock 1984, and therefore the groups of birds d id not find it necessary to flee. However, Trail 1987 found that larger mating groups, or leks, were actually more likely to get ‚spookedƒ, that is, to make head long flights, usually due to false alarms. The difference here may be due to the specific na ture of leks. Since leks are groups of males dancing and singing, trying to attract females attention, the males would need to be very careful they werent attracting predators as well. In addition, his study was done in a tropical rain forest in Suriname with a wide variety of predators, including raptors, felids and snakes. My hypothesis that exposed birds are more likely to fly than concealed birds was supported by the trend of 32% exposed birds flying due to raptor calls, compared with 11% of hidden birds flying. It is unusual that exposed birds had a higher flight time than hidden birds; however, only two hidden birds actually flew, so the average is not reliable. Also, hidden birds did nothing 39% of the time, compared with 21% for the exposed birds These trends supported the anti detection defense mechanism of concealment. If a bird was concealed in the leaves of a tree, it had no reason to fly away. However, cryptic coloration often allows animals to be in plain view, but still remain hidden. An e xample of this is Hoffmans Woodpecker Melanerpes hoffmanni Although this bird was exposed and solitary all three times I played raptor calls to it, it displayed no reaction every time. Although there was not much foliage, it was still difficult to spot because it was camouflaged. Therefore, had the woodpecker flown, it would have become visible. The X table showed a significant value, and the difference in frequency of flights is most apparent in the Exposed X Solitary grid, with 16 total flights Tab le 1. This combination supports both of my hypotheses that solitary birds will fly more often than

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groups and exposed birds will fly more often than hidden birds. If a bird is not using either anti detection or anti capture strategies, it makes sense that it will fly if it hears a potential threat. The One way ANOVA tests showed no relation between bird size and reaction when the entire data set was considered, but showed a trend for flight reactions to be exhibited by larger birds on average when only so litary and exposed birds were considered. The size of the bird was not a reliable predictor of its reaction to the raptor call; the smallest passerines often times only looked around, such as Yellow Throated Euphonias, Tropical Pewees, and Yellow Faced Gra ssquits Tiaris olivacea that never flew, while medium sized birds such as corvids jays flew nearly every time. The biggest bird I observed was the Cattle Egret Casmerodius albus and it showed no reaction. Raptors may have a tougher time finding the smallest birds, or it may be possible that the raptors do not bother with these smallest birds and instead look for medium sized birds, to be energy efficient. The largest birds may not even be considered prey because of their size. The data show that bir ds recognize and perceive a threat from raptor calls. The results suggest that birds use the anti detection strategy of concealment and camouflage, and the anti capture strategy of flocking. Further research should be done on raptor call recognition on a s ingle species or guild of birds to determine if raptor call recognition is specific on a lower taxonomic level or specific grouping, as previous studies have suggested. ACKNOWLEDGEMENTS I would like to thank Alan Masters for his encouragement and guidanc e on this project, Andrew Rodstrom and Tim Kuhman for their patience and answers to my endless supply of questions, and my parents for supporting me in my desire to explore the tropical forests of Costa Rica. LITERATURE CITED Alcock J. 1984. Animal Be havior: An evolutionary approach. Sinauer Associates, Inc., Sunderland, Massachusetts, USA. Buchanan J.B., C.T. Schick, L.A. brennan, and S.G. Herman. 1988. Merlin predation on wintering dunlins: hunting success and dunlin escape tactics. The Wilson Bu lletin 100: 108 118. Caldwell G.S. 1986. Predation as a selective force on foraging herons: effects of plumage color anf flocking. The Auk 103: 494 505. Fogden, M. 1993. An Annotated Checklist of the Birds of Monteverde and Penas Blancas. Litografia e Imprenta LIL, San Jose, Costa Rica. Goldman P. 1980. Flocking as a posible predator defense in dark eyed juncos. The Wilson Bulletin 92: 88 95. Haber W.A., W. Zuchowski and E. Bello. 2000. An Introduction to Cloud Forest Trees: Monteverde, Costa Rica Mountain Gem Publications, Monteverde, Costa Rica. Hauser M.D. and C. Caffrey. 1994. Anti predator response to raptor calls in wild crows, Corvus brachyrhynchos hesperis. Animal Behaviour 48: 1469 1471. Holdridge, L.R. 1967. Life Zone Ecology, Revis ed Edition. Tropical Science Center, San Jose, Costa Rica. Janzen, D.H. 1983. Costa Rican Natural History. The University of Chicago Press, Chicago, Illinois, USA. Lima S.L. and P.A. Bednekoff. Back to the basics of anti predatory vigilance: can nonvi gilant animals detect attack? Animal Behaviour 58: 537 543. Perrins C. 1979. Birds: Their Life, Their Ways, Their World. Readers Digest, USA

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Pettifor R.A. 1990. The effects of avian mobbing on a potential predator, the European kestrel, Falco tinnuncu lus. Animal Behaviour 39: 821 827. Stiles G.F., and A.F. Skutch. 1989. A Guide to the Birds of Costa Rica. Comstock Publishing Associates, Ithica, N.Y., U.S.A. Terbough, J. 1989. Where Have All the Birds Gone? Princeton University Press, Princeton, N .J., U.S.A. Trail P.W. 1987. Predation and antipredator behavior at Guianan cock of the rock leks. The Auk 104: 496 507.

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TABLES AND FIGURES Figure 1. Eighty seven songbird and 84 raptor calls were played to birds, with the abov e reactions. Differences were significant for all reactions between songbird and raptor calls. Figure 2. The Great Blawk Hawk and Collared Forest Falcon are residents, while the Semiplumbeous Hawk and Slaty Backed Forest Falcon are non residents; no sig nificant differences. Twenty one calls were played for each raptor.

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Figure 3. Average time birds stayed before they flew away Twenty three flight reactions total. Raptors 1 & 3 are residents, 2 & 4 are non residents. Raptor 1 is the Great Blawk Hawk, 2 is the Semiplumbeous Hawk, 3 is the Collared Forest Falcon, and 4 is the Slaty Backed Forest Falcon. Figure 4. Fifty one raptor calls were played for solitary birds, and 33 raptor calls were played for groups, with the indicated reactions no signifi cant differences between solitary birds and groups.

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Figure 5. 66 and 18 raptor calls were played for exposed and hidden birds, respectively. No significant differences between exposed and hidden birds for any of the reactions. Table 1. Conditions under which birds tended to show ‚flyƒ reactions in response to raptor calls, X 2 = 17.1 Solitary Group Exposed 16 5 Hidden 2 0

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APPENDIX Bird species, size in cm, sequence call # played, # of individuals, exposed e or hidden h, reactions N € ‚ noneƒ, L € ‚lookƒ, F € ‚flyƒ. Species Key: A € Grove Billed Ani, Crotophaga sulciroctris BCM € Blue Crowned Motmot, Momtus momota BGT € Blue Grey Tanager, Thraupis episcopus BJ € Brown Jay, Cyanocorax morio BWB € Black and White Becard, Pachyramphus albog riseus DCFC € Dusky Capped Flycatcher, Myiarchus tuberculifer EM € Eastern Meadowlark, Sturnella magna ET € Emerald Toucanet, Aulocorhynchus prasinus GBC € Golden Browed Chlorophonia, Chlorophonia callophrys GCFC € Gray Capped Flycatcher, Myiozetetes gran adensis GE € Great Egret, Casmerodius albus GK € Great Kiskadee, Pitangus sulphuratus GTG € Great Tailed Grackle, Quiscalus mexicanus HW € House Wren, Troglodytes aedon HWP € Hoffmans Woodpecker, Melanerpes hoffmannii ID € Inca Dove, Colombina inca KBT € Keel Billed Toucan, Ramphastos sulphuratus MIXED € Mixed species flock MO € Montezuma Oropendola, Psarocolius montezuma MR € Mountain Robin, Turdus plebejus MT € Masked Tityra, Tityra semifasciata NO € Northern Oriole, Icterus g. galbula RCNT € Ruddy Cappe d Nightingale Thrush, Catharus frantzii RCW € Rufous Capped Warbler, Basileuterus tristriatus SFC € Social Flycatcher, Myiozetetes similus ST € Summer Tanager, Piranga rubra TKB € Tropical Kingbird, Tyrannus melancholicus TP € Tropical Pewee, Contopus cine reus WTMJ € White Throated Magpie Jay, Calocitta Formosa WFP € White Fronted Parrot, Amazona albifrons YFG € Yellow faced Grazzquit, Tiaris olivacea YTE € Yellow Throated Euphonia, Euphonia hiruninacea

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Species Length cm Seq # # of indivs Exp/Hid Songb ird Rx Raptor Rx Time s A 30 3 5 E N N A 30 1 8 H N L A 30 1 3 H N N BCM 39 2 1 E N F 18 BGT 15 1 2 E N L BGT 15 3 1 E N F 24 BJ 39 2 3 E N F 25 BJ 39 1 3 E N N BJ 39 2 1 H N F 12 BJ 39 4 1 H N F 12 BWB 14 3 1 E N F 43 DCFC 16.5 1 1 E N F 34 EM 20 4 2 E N F 17 EM 20 3 1 E N F 2 ET 29 3 2 E N L ET 29 1 1 E N F 18 ET 29 3 1 H L L ET 29 4 1 H N N GBC 13 3 9 E N F 36 GCFC 16.5 1 2 E N L GCFC 16.5 3 2 E N L GCFC 16.5 3 1 E F GCFC 16.5 1 1 E N L GCFC 16.5 4 1 E N L GCFC 16.5 4 1 E N L GE 101 4 1 E N L GK 23 3 1 E F GK 23 2 1 E N F 27 GK 23 1 1 E N L GK 23 1 1 E N L GK 23 2 1 E N N GTG 43 4 1 E N F 1.5 GTG 43 3 1 E N L GTG 43 2 1 E N N HW 10 2 1 E N L HWP 18 1 1 E N N HWP 18 2 1 E N N HWP 18 3 1 E N N ID 20 2 2 E N L ID 20 4 3 E N N ID 20 3 2 H N L ID 20 4 1 E N F 40 ID 20 3 1 H N N

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KBT 47 3 1 H N L MIXED 4 4 E N N MO 50 2 2 E N L MO 50 2 10 E N L MR 24 1 1 E N L MR 24 2 1 E N L MT 21 4 1 E N F 22 NO 18 2 7 E N N RCNT 16 1 1 H L L RCW 12.5 1 1 E N F 30 SFC 16 1 3 E N F 26 SFC 16 1 2 E N L SFC 16 1 2 H N N SFC 16 3 5 H N N SFC 16 2 1 E F SFC 16 1 1 E N F 32 SFC 16 2 1 E N F 5 SFC 16 4 1 E N F 8 SFC 16 1 1 E N L SF C 16 1 1 E N L SFC 16 2 1 E N L SFC 16 2 1 E L L SFC 16 3 1 E L L SHWC 19 4 1 H N N ST 16.5 2 1 H N L ST 16.5 2 1 H N L TKB 21 4 2 E N F 18 TKB 21 2 1 E L F 14 TP 13 3 1 E N L TP 13 4 1 E N L TP 13 4 1 E N N WFMJ 46 3 1 E N F 15 WFP 25 3 2 E N L WFP 25 4 2 E N N WFP 25 3 4 H N N YFG 10 4 3 H N L YFG 10 2 1 E N L YFG 10 3 1 E N N YTE 11 2 4 E N L YTE 11 4 2 E N L YTE 11 4 2 E N L YTE 11 4 3 E N L YTE 11 3 4 E N N YTE 11 1 2 H L L