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Impact of intraspecific and interspecific competition on aggression and foraging of hummingbirds (family Trochilidae)

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Title:
Impact of intraspecific and interspecific competition on aggression and foraging of hummingbirds (family Trochilidae)
Translated Title:
Impacto de la competencia intraespecífica e interespecifica en la agresión y forrajeo de los colibríes (familia Trochilidae) ( )
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English
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Tsai, Whitney
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Competition (Biology)   ( lcsh )
Hummingbirds--Food   ( lcsh )
Birds--Behavior   ( lcsh )
Costa Rica--Puntarenas--Monteverde Zone   ( lcsh )
Competencia (Biología)
Colibríes--Alimento
Aves--Comportamiento
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Fall 2009
Ecología Tropical Otoño 2009
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Reports   ( lcsh )
Reports

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Abstract:
Hummingbirds have high metabolic needs and many aggressively compete for food. Competition is a potentially important component of resource defense but its impact on aggression and foraging of hummingbirds is not well understood. I manipulated the perception of competition by using the playback of the Coppery-headed Emerald (Elvira curpeiceps), a territorial hummingbird, and of the Violet Sabrewing (Campylopterus hemileucurus), a traplining hummingbird, to assess the impact on number of aggressive chases and foraging success of hummingbirds at feeders. This study was performed in Monteverde at the Monteverde Cloud Forest Preserve and Selvatura Park. The playbacks caused some but not all hummingbird species to be more aggressive and forage less often. Specifically, intraspecific and interspecific competition between the territorial species, increased aggression (mean value before: 1±0.34; mean value after: 2.92±0.29) and decreased foraging time (mean value before: 12±3.21; mean value after: 6.75±1.95). Interspecific competition between the trapliner and the territorialist increased aggression for the territorialist (mean value before: 0.29±0.50; mean value after: 2.71±0.29), but not the trapliner (mean value before: 2±0.63; mean value after: 2.4±0.66;), while foraging was not affected for either (territorialist, mean value before: 14.53±3.75; mean value after: 10.88±3.84: trapliner, mean value before: 9.57±2.22; mean value after: 9.38±1.41). These results suggest that intraspecific competition impacts foraging and aggression more than interspecific competition, and that foraging behavior plays a role in competition.
Abstract:
Los colibríes tienen necesidades metabólicas altas y por esta razón muchos compiten agresivamente por la comida. La competencia es un elemento potencialmente importante de la defensa de los recursos, pero su impacto en la agresión y la alimentación de los colibríes no es bien conocido. Manipule la percepción de la competencia por el uso de la reproducción entre el Coppery-headed Emerald (Elvira curpeiceps), un colibrí territorial, y el Violet Sabrewing (Campylopterus hemileucurus), un colibrí rutera, para evaluar el impacto en el número de persecuciones agresivas y el éxito de forrajeo de los colibrís en los comedores. Este estudio se realizó en Monteverde, Costa Rica en la Reserva Bosque Nuboso de Monteverde y en el parque de Selvatura. Las reproducciones causaron algunas pero no todas las especies de colibríes a ser más agresivas y forrajear con menos frecuencia. Específicamente, había competencia intraespecifica e interespecifica entre las especies territoriales, un aumento de agresión (promedio del valor antes: 1±0.34; promedio del valor después: 2.92±0.29), y una disminución en el tiempo de forrajeo (promedio del valor antes: 12±3.21; promedio del valor después: 6.75±1.95). La Competencia interespecífica entre el colibrí rutera y el colibrí territorial aumentaron la agresión del colibrí territorial (promedio del valor antes: 0.29±0.50; promedio del valor después: 2.71±0.29), pero no del colibrí rutera (promedio del valor antes: 2±0.63; promedio del valor después: 2.4±0.66), y el forrajeo no se vio afectado por ninguno de los colibríes (territorial: promedio del valor antes: 14.53±3.75; promedio del valor después: 10.88±3.84: rutera: promedio del valor antes: 9.57±2.22; promedio del valor después: 9.38±1.41). Estos resultados sugieren que la competencia intraespecifica impacta el forrajeo y la agresión más que la competencia interespecifica, y que el comportamiento de forrajeo juega un papel en la competencia.
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Text in English.
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Impact of Intraspecific and Interspecific Competition on Aggression and Foraging of Hummingbirds (Family Trochilidae) Whitney Tsai Department of Biology, Occidental College ABSTRACT Hummingbirds have high metabolic needs and many aggressively compete for food. Competition is a potentially important component of resource defense but its impact on aggression and foraging of hummingbirds is not well understood. I manipulated the perception of competition by using the playback of the Coppery headed Emer ald ( Elvira curpeiceps ), a territorial hummingbird, and of the Violet Sabrewing ( Campylopterus hemileucurus ) a traplining hummingbird, to assess the impact on number of aggressive chases and foraging success of hummingbirds at feeders. This study was per formed in Monteverde at the Monteverde Cloud Forest Preserve and Selvatura Park. The playbacks caused some but not all hummingbird species to be more aggressive and forage less often. Specifically, intraspecific and interspecific competition between the territorial species, increased aggression (mean value before: 10.34; mean value after: 2.920.29) and decreased foraging time (mean value before: 123.21; mean value after: 6.751.95). Interspecific competition between the trapliner and the territorialis t increased aggression for the territorialist (mean value before: 0.290.50; mean value after: 2.710.29), but not the trapliner (mean value before: 20.63; mean value after: 2.40.66;), while foraging was not affected for either (territorialist, mean valu e before: 14.533.75; mean value after: 10.883.84: trapliner, mean value before: 9.572.22; mean value after: 9.381.41). These results suggest that intraspecific competition impacts foraging and aggression more than interspecific competition, and that foraging behavior plays a role in competition. RESUMEN Los colibrs tienen necesidades metablicas altas y por este razn compiten agresivamente para comida. La competencia es potencialmente importante por el tpico de defensa de recursos, pero su impact o en agresin y forrajeando de colibrs no es bien conocido. Manipule competencia por playback entre el Coppery headed Emerald ( Elvira curpeiceps ), una colibr territorio, y el Violet Sabrewing ( Campylopterus hemileucurus ) una colibr rutera, para aprende r el impacto del playback en dos variables, persiguiendose agresivos y xito de forraje de colibrs en comedores. Este estudio estaba hecho en Monteverde, Costa Rica en el Monteverde Cloud Forest Reserve y Selvatura Park. Los playback causaron agresin mas alta y menos tiempo forrajeando en algunas, pero no todos, de los especies de colibrs. Especficamente, habia competencia interspecfico y intraspecfico entre los especies territorios, un aumento de agresin ( promedio del valor antes : 10.34; promedio d el valor despus : 2.920.29) y un disminucin en tiempo de forraje ( promedio del valor antes : 123.21; promedio del valor despues : 6.751.95) Competencia interspecfico entre la colibr rutera y la colibr territorio aumentaron la agresin de la colibr territorio ( promedio del valor antes : 0.290.50; promedio del valor despus : 2.710.29) pero no de la colibr rutera ( promedio del valor antes : 20.63; promedio del valor despus: 2.40.66 ) y forrajeando no cambio por ninguna de las colibrs (territorial : promedio del valor antes : 14.533.75; promedio del valor despus: 10.883.84: rutera: promedio del valor antes : 9.572.22; promedio del valor despus : 9.381.41) Estos resultados sugieran que competencia intraspecifico impacta forrajeando y agresin m s que competencia interspecifico, y el comportamiento de forraje es parte del rol en competencia.

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INTRODUCTION Tropical hummingbirds have high metabolic rates and must consume half their weight in nectar a day (Hainsworth and Wolf 1972). Some hummingbir ds aggressively compete for food, and are called territorialists; while others, called trapliners, avoid direct competition by using widely dispersed nectar resources that are not energetically feasible to defend (Stiles and Wolf 1970; Long 1997). Aggress ive behaviors in hummingbirds Long 1997). These aggressive interactions can be expensive and should be minimized while still restricting access of interlopers (Stil es and Skutch 1970; Feinsinger 1979). Aggressive encounters between hummingbird species can impact foraging. Both a traplining species and a territorial species decreased their food intake when with another individual of the same species (Tiebout, 1993) Alternatively, in this same experiment, just the trapliner decreased food intake when the two species were together. displaced and excluded from rich food sources by mor e aggressive, territorial species (1996). Therefore, competition is particularly costly for trapliners, though intraspecific and interspecific competition between territorial species is also important When more individuals and species are present at fee ders, aggressive playback calls cause both trapliners and territorial species to lower their foraging efforts (Gifford, 2009). In this case, the relative impact of intra and interspecific competition were not directly assessed, but playback of both territo rial and traplining species lowered visits to feeders. This study focuses on the affects of aggressive calls of two hummingbird species, the Coppery headed Emerald ( Elvira curpeiceps ), a territorial species, and the Violet Sabrewing ( Campylopterus hemileuc urus ) a traplining species, on the foraging time and aggression of other individuals at feeders. I used aggressive playback calls to manipulate perceived competition at artificial feeders by different species. I hope to discover the effect of aggressive interactions in response to both intraspecific and interspecific competition. MATERIALS AND METHODS Study Species This study focuses on three species of hummingbirds: the Violet Sabrewing ( VSW ) the Coppery headed Emerald ( CHE), and the Purple throated Mountain gem ( Lampornis calolaema ; PTMG ) The average size of the Violet Sab rewing is 15 cm with males having an average weight of 11.5g and females 9.5g. It is a very large, trapliner that is less aggressive than its size suggests at flowers (Stiles an d Skutch 1989). The Pur ple throated Mountain gem is a smaller species, with an average size of 10.5cm, males weighing 6.0g on average and females 4.8g. It is very aggressive, territorial hummingbird and often calls while foraging (Stiles and Skutch 1989) The territor ial Coppery headed Emerald is endemic to Costa Rica and is the smallest of the three species with an average size of 7.5cm, and average weights for males and females of 3.2g (Stiles and Skutch 1989; Garrigues and Dean 2007).

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Study Sites Th is study was conducted between October 24, 2009 and November 17, 2009 in Monteverde, Costa Rica. Playback recordings were made at the hummingbird garden at the Monteverde Cloud Forest Pr eserve. Observations were made at the hummingbird gardens of the Mon teverde Cloud Forest Pr eserve and Selvatura Park. Playback Recordings Multiple two minute long recordings were made inside the hummingbird garden using a Marantz PMD660 digital recorder. Aggressive calls of the Violet Sabrewing and Coppery headed Emeral d were chosen and created separately using the Raven Software. Each playback consisted of a repeated pattern of three seconds of the aggressive call and seven seconds of silence to simulate conditions in the wild. Playback Treatments Two ten minute tr eatments were performed at different hummingbird feeders in the gardens: one using the call of the Violet Sabrewing and one using the call of the Coppery headed Emerald. Each treatment consisted of five minutes of control observations without a playback call and five minutes with a playback call using an iPod and speakers placed about two meters from each feeder. For each feeder, I recor ded all aggressive interactions, determined by number of active chases, between individuals for each treatment. Three foraging observations were made during separate ten minute treatments, one for the: VSW, CHE, and PTMG Foraging time was measured in seconds using a stopwatch. I randomly selected the order in which calls were played and observations were made at each feeder. RESULTS Aggressive Behavior The mean number of aggressive interactions significantly increased for the Coppery headed Emerald in response to both the CHE call (mean value before: 10.34; mean value after: 2.920.29; paired t test: t=3.95, df=12 p=0.001) and the VS W call (mean value before: 0.290.50; mean value after: 2.710.29; paired t test: t= 6.58, df=6, p=0.0003; Fig. 1). Conversely, aggression of the Violet Sabrewing was relatively unaffected by the CHE call (mean value before: 20.63; me an value after: 2.40.66; paired t test: t=0.51, df=9, p=0.31), but its aggression significantly increased in response to the VS W call (mean value before: 20.58; mean value after: 4.41.12; paired t test: t=3.59, df=9, p=0.003; Fig. 2). Aggressive intera ctions increased for the Purple throated Mountain gem in response to both the CHE call (mean value before: 1.750.50; mean value after: 3.060.61; paired t test: t=2.23, df=15, p=0.02) and the VS W call (mean value before: 1.250.30; mean value after: 2.42 0.68; paired t test: t= 1.98, df=11, p=0.04; Fig. 3).

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FIG. 1. The average number of aggressive interactions with standard error bars for the Coppery headed Emerald in response to the calls of CHE and VSW. Both playbacks significantly increased number of aggressive interactions. FIG. 2. The average number of aggressive interactions with standard error bars for the Violet Sabrewing in response to the calls of CHE and VSW. The VSW playback significantly increased number of aggressive attacks.

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FIG. 3 The average number of aggressive interactions with standard error bars for the Purple throated Mountain gem in response to the calls of CHE and VSW. Both playbacks significantly increased number of aggressive attacks. Foraging Time The foraging time for the Coppery headed Emerald was significantly lowered in response to the CHE call (mean value before: 123.21; mean value after: 6.751.95; ANOVA: F=4.54, df=1, p=0.04), but not in response to the VS W call (mean value before: 14.533.75; mean value afte r: 10.883.84; ANOVA: F=0.76, df=1, p=0.39; Fig. 5). The foraging time of the Violet Sabrewing was not affected by either of the playback calls: CHE (mean value before: 9.572.22; mean value after: 9.381.41; ANOVA: F=0.06, df=1, p=0.81) or VS W (mean val ue before: 9.442.34; mean value after: 8.291.84; ANOVA: F=0.14, df=1, p=0.71; Fig. 6). The foraging time of the Purple throated Mountain gem was significantly lowered in response to the CHE call (mean value before: 15.263.5; mean value after: 7.321.46 ; ANOVA: F= 7.74, df=1, p=0.007), but not to the VS W call (mean value before: 5.671.24; mean value after: 7.31.52; ANOVA: F=1.39, df=1, p=0.25; Fig. 7).

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Fig. 5. Mean foraging time in seconds with standard errors bars for the Coppery headed Emerald in response to the calls of CHE and VSW. The CHE playback significantly reduced foraging time. FIG. 6. Mean foraging time in seconds with standard error bars for the Violet Sabrewing in response to the calls of CHE and VSW. Neither playback significantly decreased foraging time.

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FIG. 7. Mean foraging time in seconds with standard error bars for the Purple Throated Mountain gem in response to the calls of CHE and VSW. The CHE playback significantly decreased foraging time. DISCUSSION Intraspecific c ompetition had a large impact on the behavior of the Coppery headed Emerald, responding to the playback of its conspecific with both an increase in aggression an d a decrease in foraging time, while interspecific competition only affected aggression. This aggression can be explained by the Coppery headed Emerald s territorial foraging behavior. Territorial hummingbirds must make the trade off between the high energetic cost of protecting a rich food source and the guarantee of readily available food (Feins inger 1979). Therefore, the addition of an aggressive call to the normal chatter of the hummingbird garden represented an increase in competition, which caused the Coppery headed Emerald to be more aggressive. Furthermore, it can be inferred that the red uction in foraging time observed with the sound of a playback call can be attributed to how the playback call increases aggression; therefore increase in aggression leads to a decrease in foraging time for this territorial hummingbird. Conversely, the cal l of the Violet Sabrewing increased the aggressive behavior of the Coppery headed Emerald, showing that the territorial hummingbird is responding to an increase in competition. This increase in aggression to both intra and interspecific competition reflec The Violet Sabrewing responded more aggressively to intraspecific competition than to interspecific competition, but its foraging time was never affected. The rich, constant food supply that the feeders provide increases aggression towards conspecifics in defense of the food in some species, like the Violet Sabrewing (Wolf et al. 1976). However, despite the presence of competition, the Violet Sabrewing continues foraging. T rapliners spend much o f their time in flight searching for food sources and are efficient

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foragers once they find a food source (C olwell 1973; Feinsinger 1976). In this study, Violet Sabrewing aggression replaces the time allocated for searching and maintains a constant foragi ng rate; this reflects its priority as a trapliner to forage and feed The aggression of the Violet Sabrewing was not affected by the addition of interspecific competition simulated by the Coppery headed Emerald call. This supports the trapliner behavior of the Violet Sabrewing in that it shows that the trapliner will be less or not aggressive in competition with a territorialist. The response of the Purple throated Mountain gem to the call of the Coppery headed Emerald and the Violet Sabrewing, exemplifi es how foraging behaviors influence interspecific competition. Simulated interspecific competition between the territorial Purple throated Mountain gem and the trapliner, the Violet S abrewing, showed an increase in aggression, but no impact on foraging ti me from the territorial hummingbird, similarly to the response of the Coppery headed Emerald. The territorial, Purple throated Mountain gem responded more aggressively and with less foraging to the call of the Coppery headed Emerald. These responses are similar to those seen during intraspecific competition in the Coppery headed Emerald and can be attributed to the fact that their foraging strategies are similar (Stiles and Skutch 1989) The abundant food sources provided at the hummingbird feeders may s trengthen interspecific competition between these two species because where in the wild these species specialize on different flowers and different heights within the canopy, in the garden they are competing for the same resources (Stiles and Skutch 1989) These artificial conditions could increase the interspecific competition between these two territorial species because of overlapping foraging strategies causing their responses to be similar to intra specific competition This study showed that both intr aspecific competition and interspecific competition affect behavior of hummingbirds. Intraspecific competition made more of an impact on aggression and foraging time than interspecific competition between a trapliner and a territorial hummingbird. Unlike between a trapliner and a territorialist did not prove more costly for either species in terms of foraging. Alternatively, intra and interspecific competition showed similar responses in two territorial humming birds, which could be a result of the environment created at feeders. Therefore, foraging behavior of hummingbirds determines the affects of competition on aggression and foraging time. These conclusions expand on the study of Gifford, differentiating th e effects of intra and interspecific competition on hummingbird behavior. Also, for intraspecific and interspecific competition between territorial hummingbirds, it appears that increased aggression in response to the playback calls decreases foraging tim e. Future studies could test the relationship between aggression and foraging time more closely to determine the direct costs of aggressive behavior on foraging. Another study could focus on eliminating the effects of an unlimited food source and testing competition at flower patches in the forest to determine if these findings still hold tru e. ACKNOWLEDGEMENTS I would like to thank Yimen Araya for guiding me through all parts of my project and answering my endless questions about statistics. Alan Mast ers, for his support and guidance in developing and carrying out my project. I would also like to thank Roberto Wesson for his knowledge of hummingbirds. Lastly, I would like to thank the Monteverde Cloud Forest Preserve and Selvatura Park for allowing m e to conduct

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my experiments on their feeders and also to the Selvatura shuttle drivers for giving me rides to my study site. LITERATURE CITED Colwell, R. K. 1973. Competition and coexistence in a simple tr opical community. The American Naturalist. 107 (958): 737 760. Feinsinger, P. 1976. Organization of a tropical guild of nectarivorous birds. Ecological Monographs. 46 (3): 257 291. Feinsinger, P., R. K. Colwell, J. Terborgh, S. B. Chaplin. 1979. Elevation and the morphology, flight energet ics, and foraging ecology of tropical hummingbirds. The American Naturalist. 113 (4): 481 496. Garrigues, R., and R. Dean. 2007. The birds of Costa Rica: A field guide. Comstock Publishing Associates, Ithaca, New York. Gifford, C. 2009. Impact o f antagonistic calls on foraging behavior in hummingbirds. In Tropical Ecology and Conservation. CIEE, Monteverde, Costa Rica. Summer 2009: 48 53. Hainsworth, F. R., L. L. Wolf. 1972. Energetics of nectar extraction in a small, high altitude, tropica l hummingbird, Selaphorus flammula Journal of Comparative Physiology A. 80 (4): 377 387. Long, K. 1997. Hummingbirds: a wildlife handbook. Johnson Books, Boulder, Colorado. Stiles, F. G., and A. F. Skutch. 1989. A guide to the birds of Costa Rica Comstock Publishing Associates, Ithaca, New York. Stiles, F. G. and L. L. Wolf. 1970. Hummingbird territoriality at a tropical flowering tree. The Auk. 87 (3): 467 491. Tiebout, H. M. 1993. Mechanisms of competition in tropical hummingbirds: met abolic costs for losers and winners. Ecology. 74 (2): 405 418. Tiebout, H. M. 1996. Costs and benefits of interspecific dominance rank: are subordinates better at finding novel food locations? Animal Behavior. 51: 1375 1381. Wolf, L. L., F. G. Stil es, and F. R. Hainsworth. 1976. Ecological organization of a tropical, highland hummingbird community. Journal of Animal Ecology. 45 (2): 349 379.


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Impacto de la competencia intraespecfica e interespecifica en la agresin y forrajeo de los colibres (familia Trochilidae)
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Impact of intraspecific and interspecific competition on aggression and foraging of hummingbirds (family Trochilidae)
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c 2009-11
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Hummingbirds have high metabolic needs and many aggressively compete for food. Competition is a potentially important component of resource defense but its impact on aggression and foraging of hummingbirds is not well understood. I manipulated the perception of competition by using the playback of the Coppery-headed Emerald (Elvira curpeiceps), a territorial hummingbird, and of the Violet Sabrewing (Campylopterus hemileucurus), a traplining hummingbird, to assess the impact on number of aggressive chases and foraging success of hummingbirds at feeders. This study was performed in Monteverde at the Monteverde Cloud Forest Preserve and Selvatura Park. The playbacks caused some but not all hummingbird species to be more aggressive and forage less often. Specifically, intraspecific and interspecific competition between the territorial species, increased aggression (mean value before: 10.34;
mean value after: 2.920.29) and decreased foraging time (mean value before: 123.21; mean value after: 6.751.95). Interspecific competition between the trapliner and the territorialist increased aggression for
the territorialist (mean value before: 0.290.50; mean value after: 2.710.29), but not the trapliner (mean value before: 20.63; mean value after: 2.40.66;), while foraging was not affected for either (territorialist,
mean value before: 14.533.75; mean value after: 10.883.84: trapliner, mean value before: 9.572.22; mean value after: 9.381.41). These results suggest that intraspecific competition impacts foraging and aggression more than interspecific competition, and that foraging behavior plays a role in competition.
Los colibres tienen necesidades metablicas altas y por esta razn muchos compiten agresivamente por la comida. La competencia es un elemento potencialmente importante de la defensa de los recursos, pero su impacto en la agresin y la alimentacin de los colibres no es bien conocido. Manipule la percepcin de la competencia por el uso de la reproduccin entre el Coppery-headed Emerald (Elvira curpeiceps), un colibr territorial, y el Violet Sabrewing (Campylopterus hemileucurus), un colibr rutera, para evaluar el impacto en el nmero de persecuciones agresivas y el xito de forrajeo de los colibrs en los comedores. Este estudio se realiz en Monteverde, Costa Rica en la Reserva Bosque Nuboso de Monteverde y en el parque de Selvatura. Las reproducciones causaron algunas pero no todas las especies de colibres a ser ms agresivas y forrajear con menos frecuencia. Especficamente, haba competencia intraespecifica e interespecifica entre las especies territoriales, un aumento de agresin (promedio del valor antes: 10.34; promedio del valor despus: 2.920.29), y una disminucin en el tiempo de forrajeo (promedio del valor antes: 123.21; promedio del valor despus: 6.751.95). La Competencia interespecfica entre el colibr rutera y el colibr territorial aumentaron la agresin del colibr territorial (promedio del valor antes: 0.290.50; promedio del valor despus: 2.710.29), pero no del colibr rutera (promedio del valor antes: 20.63; promedio del valor despus: 2.40.66), y el forrajeo no se vio afectado por ninguno de los colibres (territorial: promedio del valor antes: 14.533.75; promedio del valor despus: 10.883.84: rutera: promedio del valor antes: 9.572.22; promedio del valor despus: 9.381.41). Estos resultados sugieren que la competencia intraespecifica impacta el forrajeo y la agresin ms que la competencia interespecifica, y que el comportamiento de forrajeo juega un papel en la competencia.
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Text in English.
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Hummingbirds--Food
Birds--Behavior
Costa Rica--Puntarenas--Monteverde Zone
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Competencia (Biologa)
Colibres--Alimento
Aves--Comportamiento
Costa Rica--Puntarenas--Zona de Monteverde
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Tropical Ecology Fall 2009
Ecologa Tropical Otoo 2009
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Reports
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CIEE
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