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Aggressive behavior of hummingbirds and their response to nectar concentrations

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Title:
Aggressive behavior of hummingbirds and their response to nectar concentrations
Translated Title:
El comportamiento agresivo de los colibríes y su respuesta a las concentraciones de néctar ( )
Physical Description:
Book
Language:
English
Creator:
Matheson, Emily
Publication Date:

Subjects

Subjects / Keywords:
Hummingbirds--Food   ( lcsh )
Birds--Behavior   ( lcsh )
Pollination by Animals   ( lcsh )
Costa Rica--Puntarenas--Monteverde Zone   ( lcsh )
Colibríes--Alimento
Aves--Comportamiento
Polinizado por animales
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Summer 2004
Ecología Tropical Verano 2004
Genre:
Reports   ( lcsh )
Reports

Notes

Abstract:
As pollinators of many flowers in Costa Rica, the foraging behavior of hummingbirds has been studied many times in the past. The Monteverde area hosts many different hummingbird species all throughout the year. Over time, as the landscape changes and flower abundance fluctuates, it is necessary to study their competitive interactions as well as their abilities to respond to these changes. This particular study quantified aggressiveness in four hummingbird species at feeders in Monteverde. Response to a change in nectar concentration (30% to 10%) was also quantified and then compared between each species (Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus, and Heliodoxa jacula). The purpose of this study was to determine if a positive relationship existed between hummingbird aggressiveness and response to nectar concentration. A chi-squared test determined which species were aggressively dominant over other species. Lampornis calolaema showed dominance over C. hemilecurus and H. jacula. Eupherusa eximia showed dominance only over L. calolaema. Simple regression lines were plotted with the number of visits over time by each species to the two nectar concentrations. The slopes of these lines were then compared to determine if certain species were more responsive than others to changes in nectar concentrations. Results showed that the more aggressive species were not more responsive to change.
Abstract:
Como polinizadores de muchas flores en Costa Rica, el comportamiento de forrajeo de los colibríes ha sido estudiado muchas veces en el pasado. En la región de Monteverde hay muchas especies de colibríes durante todo el año. Con el tiempo el uso de la tierra cambia y la abundancia de las flores cambia y es necesario estudiar las interacciones competitivas de los colibríes y sus habilidades para responder a estos cambios. Este estudio particular cuantificó la conducta agresiva en cuatro especies de colibríes en comederos en Monteverde. También se cuantificó la respuesta a cambios en las concentraciones de azúcar (30% a 10%) y luego se comparó entre las siguientes especies de colibríes (Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus, y Heliodoxa jacula). El propósito de este estudio fue determinar si existía una relación positiva entre la agresividad de los colibríes y su repuesta a los cambios de concentración de azúcar. Se usó un análisis de Chi-square para determinar cuáles especies de colibríes eran más agresivas que otros. Lampornis calolaema exhibió dominancia sobre C. hemilecurus y H. jacula. Eupherusa eximia exhibió dominancia sobre L. calolaema. Se usaron los grados de inclinación de regresiones simples donde se relacionó el número de visitas de cada especie de colibrí sobre el tiempo en las dos concentraciones de azúcar. Las inclinaciones de estas líneas se compararon para determinar si algunas especies respondían más que otros a cambios en las concentrares de azúcar. Los resultados indicaron que los colibríes más agresivas no respondían más a los cambios.
Language:
Text in English.
General Note:
Born Digital

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University of South Florida Library
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University of South Florida
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usfldc doi - M39-00391
usfldc handle - m39.391
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SFS0001560:00001


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As pollinators of many flowers in Costa Rica, the foraging behavior of hummingbirds has been studied many times in the past. The Monteverde area hosts many different hummingbird species all throughout the year. Over time, as the landscape changes and flower abundance fluctuates, it is necessary to study their competitive interactions as well as their abilities to respond to these changes. This particular study quantified aggressiveness in four hummingbird species at feeders in Monteverde. Response to a change in nectar concentration (30% to 10%) was also quantified and then compared between each species (Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus, and Heliodoxa jacula). The purpose of this study was to determine if a positive relationship existed between hummingbird aggressiveness and response to nectar concentration. A chi-squared test determined which species were
aggressively dominant over other species. Lampornis calolaema showed dominance over C. hemilecurus and H. jacula. Eupherusa eximia showed dominance only over L. calolaema. Simple regression lines were plotted with the number of visits over time by each species to the two nectar concentrations. The slopes of
these lines were then compared to determine if certain species were more responsive than others to changes in nectar concentrations. Results showed that the more aggressive species were not more responsive to change.
Como polinizadores de muchas flores en Costa Rica, el comportamiento de forrajeo de los colibres ha sido estudiado muchas veces en el pasado. En la regin de Monteverde hay muchas especies de colibres durante todo el ao. Con el tiempo el uso de la tierra cambia y la abundancia de las flores cambia y es necesario estudiar las interacciones competitivas de los colibres y sus habilidades para responder a estos cambios. Este estudio particular cuantific la conducta agresiva en cuatro especies de colibres en comederos en Monteverde. Tambin se cuantific la respuesta a cambios en las concentraciones de azcar (30% a 10%) y luego se compar entre las siguientes especies de colibres (Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus, y Heliodoxa jacula). El propsito de este estudio fue determinar si exista una relacin positiva entre la agresividad de los colibres y su repuesta a los cambios de concentracin de azcar. Se us un anlisis de Chi-square para determinar cules especies de colibres eran ms agresivas que otros. Lampornis calolaema exhibi dominancia sobre C. hemilecurus y H. jacula. Eupherusa eximia exhibi dominancia sobre L. calolaema. Se usaron los grados de inclinacin de regresiones simples donde se relacion el nmero de visitas de cada especie de colibr sobre el tiempo en las dos concentraciones de azcar. Las inclinaciones de estas lneas se compararon para determinar si algunas especies respondan ms que otros a cambios en las concentrares de azcar. Los resultados indicaron que los colibres ms agresivas no respondan ms a los cambios.
546
Text in English.
650
Hummingbirds--Food
Birds--Behavior
Pollination by Animals
Costa Rica--Puntarenas--Monteverde Zone
4
Colibres--Alimento
Aves--Comportamiento
Polinizado por animales
Costa Rica--Puntarenas--Zona de Monteverde
653
Tropical Ecology Summer 2004
Ecologa Tropical Verano 2004
655
Reports
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CIEE
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t Monteverde Institute : Tropical Ecology
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u http://digital.lib.usf.edu/?m39.391



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1 Aggressive behavior of hummingbirds and their response to nectar concentrations Emily Matheson Department of Kinesiology, University of Colorado, Boulder ABSTRACT As pollinators of many flowers in Costa Rica, the foraging behavior of hummingbirds has b een studied many times in the past. The Monteverde area hosts many different hummingbird species all throughout the year. Over time, as the landscape changes and flower abundance fluctuates, it is necessary to study their competitive interactions as well as their abilities to respond to these changes. This particular study quantified aggressiveness in four hummingbird species at feeders in Monteverde. Response to a change in nectar concentration (30% to 10%) was also quantified and then compared between each species ( Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus and Heliodoxa jacula ). The purpose of this study was to determine if a positive relationship existed between hummingbird aggressiveness and response to nectar concentration. A chi squared test determined which species were aggressively dominant over other species. Lampornis calolaema showed dominance over C. hemilecurus and H. jacula Eupherusa eximia showed dominance only over L. calolaema Simple regression lines were pl otted with the number of visits over time by each species to the two nectar concentrations. The slopes of these lines were then compared to determine if certain species were more responsive than others to changes in nectar concentrations. Results showed that the more aggressive species were not more responsive to change. RESUMEN Como polinizadores de muchas flores en Costa Rica, el comportamiento de forrajeo de los colibres ha sido estudiado muchas veces en el pasado. En la regin de Monteverde hay m uchas especies de colibres durante todo el ao. Con el tiempo el uso de la tierra cambia y la abundancia de las flores cambia y es necesario estudiar las interacciones competitivas de los colibres y sus habilidades para responder a estos cambios. Este estudio particular cuantific la conducta agresivo en cuatro especies de colibres en comederos en Monteverde. Tambin se cuantific la respuesta a cambios en las concentraciones de azcar (30% a 10%) y luego se compar entre las siguientes especies de co libres ( Lampornis calolaema, Eupherusa eximia, Campylopterus hemilecurus y Heliodoxa jacula ). El propsito de este estudio fue determinar si exista una relacin positiva entre la agresividad de los colibres y su repuesta a los cambios de concentracin de azcar. Se us un anlisis de Chi square para determinar cuales especies de colibres eran mas agresivos que otros. Lampornis calolaema exhibi dominancia sobre C. hemilecurus y H. jacula Eupherusa eximia exhibi dominancia sobre L. calolaema Se u saron los grados de inclinacin de regresiones simples donde se relacion el numero de visitas de cada especie de colibr sobre el tiempo en las dos concentraciones de azcar. Las inclinaciones de estas lneas se compararon para determinar si algunas esp ecies eran mas respondan mas que otros a cambios en las concentrares de azcar. Los resultados indicaron que los colibres mas agresivas no eran respondan mas a los cambios. INTRODUCTION

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2 Hummingbirds have been thought to have a great capacity for l earning about their food source, as they can learn from trial and error (Long 1997). In the Monteverde area, there is an abundance of different species of hummingbirds, many of which play an important role in plant pollination (Feisinger and Murcia 1996) Hummingbird behavior and role in pollination under natural and altered settings have been extensively studied (Long 1997). Some species are known to be more aggressive than other species (Stiles and Skutch 1989). One study from Monteverde concluded that larger, more aggressive birds have a preference for higher sugar concentrations (Seifert and Tuscano 1999). Their preference of sugar concentration is known to be on average 20% (Baker 1975). As landscapes are altered, specific hummingbird species c ould be affected due to lack of response to change or the inability to out compete other species for limited nectar resources. It was discovered that hummingbirds visit disturbed sites more frequently than undisturbed sites in Monteverde, illustrating the ir importance to ecological processes in a fragmented landscape (Weidner 2001). There were two main focuses in this study. The first part involved observing and then quantifying the aggressiveness of different species: Purple throated Mountain gem ( Lampor nis calolaema ) Striped tailed Hummingbird ( Eupherusa eximia ) Violet Sabrewing ( Campylopterus hemilecurus ) and the Green crowned Brilliant ( Heliodoxa jacula ) in the Monteverde area. Second, observations were made to determine which species were most res ponsive to a change in nectar concentration. Their nectar concentration was changed from 30% sucrose to 10% sucrose. It was hypothesized that there would be a positive correlation between hummingbird aggressiveness and responsiveness to changes in sugar concentrations with the more dominant species responding more quickly to changes in nectar concentrations. METHODS Two study sites were used for observing hummingbird aggressiveness and were at Pacific side of the Tilaran mountain range and at Selvatura (1612m) near the Santa Elena Reserve on the Atlantic side. Both locations had previously established hummingbird feeders. The feeders on the Guindon farm were next to the house surrounded by pasture and forest edge. The Selvatura feeders were located near the reception surrounded by second growth forest. At the Guindon Farm, four species were observed at one feeder. Aggressiveness was quantified by counting the number of times individuals of each species displaced other individuals. The species of the displacer and displacee in each interaction was recorded. At Selvatura, the same four species were observed at one stand that had four feeders. Again, the number of displa cements by individuals of each species was counted. In preparation for observing response to nectar concentration, a 10% sugar concentration solution was made. This solution differed from the typical 30% concentration solution at Selvatura. A Reichert han d refractometer was used for measuring the sugar concentrations. The 10% concentration solution contained 0.125 liters of sugar for every 2 liters of water. Ten percent sucrose concentration solution was poured into two of the four feeders a t the Selvatura stand. The other two feeders were left with the 30% solution.

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3 One species was watched for four consecutive 25 minute periods. After every five minutes of each period, the number of times that species ate from each concentration was recor ded. At the end of the 25 minute period, the feeders were rotated on the stand, in order to determine response to change during each 5 minute period. There were five minute intervals between rotations. Data Analysis A chi squared test was used for anal yzing species aggressiveness. A chi squared value was calculated for each species. This value represented aggressiveness over another specific species. When compared between species, the species with the higher value was considered to be more dominant. For each trial pertaining to response to change in nectar concentrations, a simple regression line was constructed, plotting number of visits over time for each nectar concentration. The slope of each regression line was looked at to determine if the numb er of visits increased or decreased over time. The trends of these slopes were then used to determine if the species were learning and becoming more responsive after each trial. Slope trends of each species and aggressiveness were compared to determine if a pattern existed between aggressiveness and response to nectar changes. RESULTS Chi squared values indicated L. calolaema was dominant over C. hemilecurus and H. jacula Chi squared values indicated A. tzacatl was dominant over L. calolaema Other species did not show significant dominance over any other species. There were no trends in any of the slopes between visits to feeders over time (Table 1). No pattern was found between aggressiveness and response to change in nectar concentration. DISCUSSION The study did not find that more aggressive hummingbirds would respond more quickly to changes in nectar concentrations. None of the species demonstrated the ability to While some species showed dominance over others, they were not more responsive to a change in nectar concentration. None of the species were found to prefer one sugar concentration over the other (Figure 1). As previous studies found hummingbird species p referred higher sucrose concentrations, the average being 20% (Long 1997), it is possible that the lack of any trend in regression line slopes is due to many different individuals of each species visiting the feeders during each 5 minute observation period For future studies, measuring response of known individuals could reduce this variation. There are possible other reasons why no pattern was found between aggressiveness and response to change in nectar concentrations. Perhaps when resources are limit ed some hummingbirds become more aggressive, even if the resource does not contain their desired nectar concentration. When there is an abundance of plant species to choose from hummingbirds could be more selective of flower and sugar concentrations.

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4 A st udy that allowed each species an equal amount of feeding opportunities to different nectar concentrations would yield more accurate results. If the feeders were watched longer, it could be observed whether or not the less aggressive birds returned to the feeder once the aggressive birds left and this could be observed in feedings in absence of more aggressive species. It is also probable that a greater difference in nectar concentration would have yielded a sharper decrease in visits to the less concentra ted solution, making it easier to distinguish response times of each species. In some cases, hummingbirds will remember which flowers have been depleted of nectar and will return repeatedly to ones that refill after depletion (Long 1997). As one flower stops blooming and another begins, territorial zones may shift among species (Stiles and Skutch 1989). As the Monteverde environment changes over time, some flowers that attract specific hummingbird species may become less abundant, which could potentiall y shift territorial zones as well. The results form this study could further the knowledge in determining which species could potentially have an advantage to a limiting resource. L. caloleama being dominant over C. hemilecurus and H. jacula could poss ibly be at an advantage in the future if diversity or richness of hummingbird flowers decreases. On the other hand, if most hummingbird species do not strongly prefer specific plants, then this quality would be advantageous because they would be able to s urvive off of the available plant species in an altering environment. ACKNOWLEDGEMENTS I would like to thank Carlos Guindon for helping me organize this project, and thank his parents for allowing me to use their farm for observation. Thanks to Rachael Huerer for helping me in collecting data at Selvatura out in the rain. Maria Jost and Oliver Hyman were of great assistance in my agonizing data analysis and always had that positive attitude!! Last, I am so grateful to the cooks at the Estacion, muchas gracias para todo. !La comida era muy muy rica! LITERATURE CITED Baker, H. G. 1975. Sugar concentrations in nectars from hummingbird flowers. Biotropica. 7(1): 37 41 Feisinger, P. and C. Murcia. 1996. Interspecific pollen loss by hummingbirds visi ting flower mixtures: effects of floral architecture. Ecology 77(2): 550 560. Long, K. 1997. Hummingbird diet, food sources, and body temperature. Hummingbirds: A wildlife handbook, pp. 110 126. Johnson Publishing Company, Boulder, Colorado. Seifert M and A. Tuscano. 1999. Diet Preference, Competition and Learning in a Cloud Forest Hummingbird Community. Stiles, G. and A. Skutch. 1989. A guide to the birds of Costa Rica, pp. 208 230. Cornell University Press, Ithaca, New York. Weidner, K. 20 01. Patterns in hummingbird use of a tropical disturbance mosaic. CIEE Spring.

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6 % Sucrose Concentration Figure 1. Comparison between visits to feeders with 10% and 30% sugar concentration by four speci es of hummingbirds: Green crowned Brilliant (green), Striped tailed hummingbird, Purple throated Mountain Gem (purple), and Violet Sabrewing (violet). Bars represent one standard deviation (Mann Whitney). Number of Visits

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7 Table 1. Summary of regre ssion line slope trends during four consecutive 5 min. observation periods at four feeders with two 10% and two 30% sugar concentrated feeders. Increasingly negatively sloped 10% sucrose regression lines were used to a) Heliodoxa jacula Trial #1 Trial #2 Trial #3 Trail #4 10% Sucrose +.18 +.24 .38 .82 30% Sucrose +.14 .5 2.03 E 18 .7 b) Campylopterous hemileucurus Trial #1 Trial #2 Trial #3 Trail #4 10% Sucrose .22 +.08 +.16 .02 30% Sucrose +.48 1.12 .64 .1 c) Eupherusa eximia Trial #1 Trial #2 Trial #3 Trail #4 10% Sucrose +.14 +.72 1.46 .72 30% Sucrose +.58 +.72 1.74 1.58 d) Lampornis calolaema Trial #1 Trial #2 Trial # 3 Trail #4 10% Sucrose +.06 +.6 1.52 .12 30% Sucrose +1.04 .12 +.48 .2