Hummingbird Size, Pollen load and Pollination Efficiency Andrew Gapinski Department of Horticulture, University of Wisconsin Madison Abstract Pollinators are an important selective agent and play a role in the evolution of certain floral characteristics (Fenster, 1991). This is often the case with flower corollas, which have closely coevolved with the length and curvature of the bill or tongue of its pollinators (Stiles 1989) The purpose of this study was to d etermine the specificity of the coevolution between hummingbirds as pollinators and the species on which they forage. I also hope to examine the bill length body size relationship, pollen loads and their placements. I hypothesize that short billed hummingbirds will carry pollen from plant species with short corollas, and long billed hummingbirds will carry pollen from pl ant species with longer corollas, even though they are capable of getting nectar from shorter corolla flowers. Hummingbirds for this study were collected between October 20 and November 14, 2003 around the Estacin Biol gica Mont everde, Puntarenas, Costa R ica. When number of pollen species was plotted against bill length in a simple regression (Fig. 6), the relationship turned out to be significant (P = .0021). As bill length increases the number of pollen species found on a bird also increased. Speci es richness on the bill was significantly different then on the chest with a P value of 0.0324 and bill vs. total species of pollen was also found to be significant (P = 0.0015) (Fig. 8). Chest and bill vs. total were also showed a significant differenc e in species richness, both having P values of < 0.0001. So the females are carrying significantly more pollen species than males. When looking at body parts the greatest amount of pollen species is being carried on the bill, followed by the head and then chest. Females were determined to carry greater pollen loads then male due to male territorial behavior. Also, long billed humming birds feed mainly on long corolla flowers. Resumen Es reconocido que los polinizadores son un agente selectivo importante y juegan un papel en la evolucin de ciertas caractersticas florales (Fenster 1991). Este es a menudo el caso con las corolas de las flores, las cuales han evolucionado estrechamente c on la longitud y curvatura del pico o la lengua de sus polinizadores (Stiles 1989). El propsito de este estudio fue determinar l a especificidad de la coevoluci n entre colibres como polinizadores y las especies en las que e llos forrajean. Espero tambin examinar la relaci n entre longitud del pico y tamao del cuerpo, la carga de polen y su ubicaci n. Mi hiptesis es que los colibres con pico corto llevarn polen de especies de plantas con corolas cortas, y colibres con pico largo llevaran polen de espe cies de plantas con corolas ms largas, aunque ellos no son capaces de conseguir nctar de flores con corolas m s cortas. Los
colibres para este estudio fueron atrapados entre el 20 de octubre y el 14 de noviembre, en los alrededores de la Estacin Biol gica de Monteverde, Puntarenas, Costa Rica. Cuando se hizo la lnea de relacin entre especies de polen y l ongitud del pico en una regresi n sim ple (Fig. 6) la relacin result ser significativa (P = .0021). En tanto que aum enta la longitud del pico, el n mero de especies de polen en el pico de cada ave se increment La riqueza de especies en el pico fue significativamente diferente que en el pecho con un valor P de 0.0 324 y la longitud del pico vs. e species t otales de polen fue tambi n significativa (P = 0.0015) (Fig. 8). El pecho y el pico vs. el total tambin mostraron una diferencia significativa en la riqueza de especies., ambos con valores P de < 0.0001. De esta forma las hembras estn llevando significativamente ms polen que los machos. Cuando se ob servan las partes del cuerpo, la mayor cantidad de especies de polen se lleva en el pico, seguido de la cabeza y del pecho. Se determin que las hembras llevaban mayor carga de polen que los machos debido al comportamiento territorial de los machos. Tambi n, los colibres con pico largo se alimentan principalmente de flores con corola larga. Introduction Hummingbirds are important pollinators, especially at higher elevations of Neotropical regions. This is because as elevation increases activity by other pollinators, such as insects and bats, is limited due to cooler temperatures (Stiles 1989). Also, pollinators are important selective agents and play a role in the evolution of certain floral characteristics (Fenster 1991). This is especially true with flower corollas, which h ave closely coevolved with the length and curvature of the bill or tongue of its pollinators (Stiles 1989). It is thought that a plant species with a longer corolla tube will have fewer, more specialized pollinators, concealing their nectar from more gener alist pollinators. Plant species with shorter corollas are visited by more generalist pollinators, and are rarely pollinated exclusively by hummingbirds (Fenster 1991). Feinsinger (1986) observed that short flowers (with corolla lengths less than 2.5 cm) r eceived visits almost exclusively from birds with bill lengths less than 2.5 cm, whereas long corolla flowers (> 3.0 cm) were primarily visited by birds with a bill length greater than 3.0 cm. This relationship is thought to be the case because long, often curved flowers produce copious amounts of nectar, termed "rich flowers", and short corolla flowers secrete considerably less nectar ("moderate flowers") (Futuyma 1983). Longer billed and in most cases larger bodied birds, are therefore able and willing to travel greater distances to "trapline" often more widely scattered "rich flowers" (Futuyma l983). This relationship can also be seen between body size or wing length and proboscis length of other groups such as Sphingid moths. In this case, wing length an d body size are closely correlated with proboscis length, and furthermore correlated with the amount of time a moth can hover (Bullock 1983). Pollen transfer to conspecfics in long corolla species is enhanced by the species specific placement of pollen on the body of the pollinator and therefore is more efficient In contrast; short corolla flowers do not show the same specificity of pollen transfer. For, example Hermit pollinated plants that may flower simultaneously, place pollen at different locations, su ch as the forehead, bill, chin, to reduce the amount of pollen lost to non conspecifics (Futuyma 1983). The purpose of this study was to determine the specificity of the coevolution between hummingbirds as pollinators and the species on which they forage. This study also
examines the bill length body size relationship, pollen loads and their placements. It is hypothesized that short billed hummingbirds will carry pollen from plant species with short corollas, and long billed hummingbirds will carry pollen from plant species with longer corollas, even though they are capable of getting nectar from shorter corolla flowers. Materials and Methods Body Size vs. Bill Length Using data from Bleiweiss (1999) on the feeding and breeding behavior of hummingbirds, the average body size of males and females was compared to the average bill length of males and females of 106 hummingbird species. Simple regression tests were run for both males and females and scattergrams were produced. Paired t tests wer e run for males versus female bill length and body weight. Body Size, Bill Length, and Pollen Load Pollen load data from Feinsinger (1986) and data on body size and bill length from Bleiweiss (1999) were used to test the relationship between body size, bil l length and pollen load. In the Feinsinger (1986) study, pollen samples were collected from the Monteverde Cloud Forest Preserve, Monteverde, Costa Rica at three different locations (cutovers, treefalls, and forest). A correlation matrix was setup for ave rage pollen richness and pollen abundance for the three locations where the birds were collected, and also included bill length, body weight, and body length. A modified t test (Zar 1996) compared species richness and abundance between bird species. Birds were caught with mist nets and pollen was removed from the bill, throat, and head plumage using clear tape. Study Site Hummingbirds for this study were collected between October 20 and November 1 4, 2003 around the Estacin Biol gica Monteverde, Puntarenas, Costa Rica. Hummingbirds were collected from three different locations: a forest site at 1770 m and two forest edges, one at 1550 m and the other at 1510 m, using mist nets between the hours of 0500 0900 hrs and 1500 1700 hrs. Capture Methods Three hummingbird feeders containing 20% sucrose solution were set up for a three days acclimation period in order to attract hummingbirds to the site. After this period mist nests were placed between feeders and birds were caught on random days at d awn and dusk. Pollen was removed from the head, bill, and chest of each bird by vigorously rubbing each of them with separate, moistened cotton swabs, which were then placed in numbered wax paper envelopes (corresponding to bird and location of p ollen). Bird species, bill length, gender of bird, location of visible pollen, time of day, date, and location of catch were recorded. Bird species were identified using Guide to the Birds of Costa Rica" (Stiles, 1989). Birds were marked by cutting the far right tail feather so that recaptures could be
identified. Pollen samples were allowed to dry for at least two days before being mounted. Once dry, pollen was scraped (with toothpicks) from the swabs onto glass slides containing two drops of Permount. Slides were then cover slipped, and placed into a dry box until the Permount set. Slides were examined using a Carl Zeiss Jenna compound microscope at 100 x. A pollen morphospecies (species richness) library was created (Appendix 1) and number of pollen grains (species abundance) per morphospecies was recorded. One way ANOVA tests were run for average pollen richness versus bird species and average pollen abundance versus bird species. Simple Regression tests were used to compare bill length versus polle n species, and for bill length versus pollen abundance. Sexual Dimorphism, Pollen Load and Pollen Placement Tests of gender relationships and location of pollen on individuals were run exclusively on C. hemileucurus. Sex versus pollen species and sex versus pollen abundance relationships were looked at using t tests. T tests were also used to look at sex and body parts (pollen placement) for pollen richness and abundance. One way ANOVA tests were run to compare body pa rts (head, bill, chest) versus pollen richness and abundance. Pollen Identification and Plant Specificity Pollen morphospecies were then compared to pollen collected from local flowering plants. Pollen from flower anthers was collected using cotton swabs a nd was dried and mounted in the same way as the pollen from birds. Flowers were identified using "Common Flowering Plants of the Monteverde Cloud Forests Preserve" (Zuchowski, 1996). For pollen species found on four or more birds a one way ANOVA test was r un to compare average bill length to the pollen morphospecies. Results Species Descriptions In total 61 birds were caught from 7 different species. The following is a list of species caught and their foraging behaviors. Phaethornis guy (Green Hermit) is common to wet mountain forests from 500 2000 m on both slopes. They are known to visit flowers of Heliconia, Costus, Columnea and Razisea along regular foraging routes in understory, along edges, and subcanopy (Stiles 1989). Campylopterus hemileucurus, (V iolet Sabrewing) is found in mountain habitats throughout the country at elevations of 1500 2400 m during the breeding season and down to 1000m in north. Favorite flowers include Heliconia, bananas, and Cephaelis in understory, edges, or disrupted areas su ch as banana plantations (Stiles, 1989). Colibri thalassinus, (Green Violet ear) is most abundant on the pacific slope ranging from 1000 3000 m in elevation. It prefers open, bushy highland areas, visiting flowers of many herbs, shrubs, epiphytes, and trees (Stiles, 1989). Eupherusa eximia (Striped tailed Hummingbird) is common throughout the county at
mid elevations ranging from 300 2450 m depending on season. It prefers cool wet canopy dwellings and frequents plant families including Acanthaceae, Rubi aceae, Ericaceae, Gesneriaceae, and also Inga. Has been also known to nectar rob longer corolla flowers (Stiles, 1989). Elvira cupreiceps, (Coppery headed Emerald) inhabits elevations ranging from 700 1500m during breeding season and down to 300 m afterwar d. They prefer canopy and edges of wet forests, feeding on the small flowers of Pithecellobium, Quararibea, Guarea, Ericaaceae, Clusia, Besleria ( Stiles, 1989). Lampornis calolaema, (Purple throated Mountain Gem) ranges from 800 1000 m. They prefer foreste d steeply sloped areas, residing mostly in the canopy visiting and defending flowers ofSatyria, Cavendishia, Columnea, and Cephaelis ( Stiles, 1989). Heliodoxa jacula, (Green crown Brilliant) is found at elevations of 700 2000 m in wet highland forest. In the forest they can be found foraging in the mid understory and high into the canopy on Marrcgravia, Drymonia, and Heliconia (Stiles, 1989). Body size vs. Bill length Using the data Bleiweiss (1999), pared t tests for male vs. female bill length and body size were run on 106 hummingbird species. The tests showed that the average bill length for males was 2.189 cm 0.735 and for females 2.261mm 0.716 (t = 5.17, P < 0 .001, df = 104). The body size t tests showed that average body weight for male was 5.48 g 2.19 and for females 4.98 gl.71 (t = 7.04, P<.0001, df = 104). So, though males tend to have a greater body mass than females, females tended to have longer bill l engths. When bill length is plotted against body weight, in a simple regression, bill length increases linearly with body mass in both males and females (P < 0.0001 for both males and females; Fig. 1 and 2).
Body Size, Bill Length and Pollen Load A correlation matrix of body size, bill length, and pollen load, revealed six cases in which there was a significant trend (R value > 0.755). There were significant correlations between bill length and body weight (R = .860), body weight and body length (R study. There were also significant correlations for pollen richness and pollen abundance for all three of the habitats in the study (Cutovers R= .926, Treefalls R = .903, Forest s R = .910). A simple regression test revealed that although there were correlations, they were not significant in all cases. Pollen richness vs. pollen abundance in Cutcover (P = .0238) and Treefalls (P = 0.0360) were the only significant relationships. I n both cases as pollen abundance increases, pollen richness also increases. A modified t test (Zar, 1996) was then run to compare actual species abundance between bird species. No significant difference was found, because the variation in pollen load betwe en species was too large. In comparison, both results showed similar trends, but the current study revealed strong significance in some areas. When number of pollen species was plotted against bill length in a simple regression (Fig. 3), the relationship t urned out to be significantly (P = .0021). As bill length increases the number of pollen species found on a bird also plot but failed to give a significant regression li ne.
A simple regression was also run for bill length vs. pollen abundance (Fig. 4). This relation was not significant with a P value of .1021. The same (no significance)
data, no significant difference was found with pollen abundance between bird species (P value = 0.7527). But there was a significant difference with average pollen richness between bird species (P value = 0.7527). But there was a significant difference with average pollen richness between bird species (P=0.0463). Significant differences were found between: Coppery headed Emerald and Green Hermit (P = 0.0449), Green Hermit and Green Violet ear (P = 0.0231), Green hermit and Green crowned Brilliant (P=0.0192), Green Violet ear and Violet Sabrewing (P=0.0481), and finally between Green crowned and Violet Sabrewing (P= 0.0303). All Sexual Dimorphism, Pollen Load and Pollen Placement Pollen richness on the head, bill and chest was examined for males and females of Campylopterus hemileucurus An ANOVA test was run between sexes and a significant difference w as found between the two (F = 1.599, df = 3, P < 0.0001,). Species richness on the bill was significantly different then on the chest with a P value of 0.0324 and bill vs. total species of pollen was also found to be significant (P = 0.0015; Fig. 5). Chest and bill vs. total also showed a significant difference in species richness, both having P values of < 0.0001. So the females are carrying significantly more pollen species than males. When looking at body parts the greatest amount of pollen species is be ing carried on the bill, followed by the head and then chest.
Pollen abundance on the head, bill, and chest were compared for male and females of Campylopterus hemileucurus. An ANOVA test was run between sexes and no significant differences were found b etween the two (P < .1917; Fig.6). Although there was no statistical significance between pollen loads there was a definite trend with pollen load on the bill vs. chest (P value of .0791). Again, as in the case of richness females are carrying a slightly g reater amount of pollen. Greater amounts are found on the bill then the head or chest. Pollen Identification and Plant Specificity In total, 21 plant morphospecies (Appendix 1) were found and 5 of these were identified to species. Of the 21 morphospecies, 8 of them were found on more than four birds. A one way ANOVA test that compared average bill length to the pollen morphospecies (F ig. 7), revealed a significant difference between some of these 8 morphospecies (F = 4.098, df = 7, P = 0.0016). These relationships were: E and S ( Cavendisha spp .) (P < 0.0001), F and S (P = 0.0005), G ( Drymonia rubra ) and S (P < 0.0001), J ( Justicia aure a ) and S (P < 0.0001), K ( Poikilacanthus macranthus) and S (P = 0.0023), L and S (P = 0.0012), and O and S (P= 0.0002).
Table 1. Plant species or pollen morphospecies, flower length and bill length comparison Morphospecies and Species Corolla length (cm) Average Bill length (cm) E 3.47 F 3.525 G: Drymonia rubra 4 5 3.63 J: Justicia aurea 3 3.73 K: Poikilacanthus macranthus 8 3.24 L 3.32 O 3.44 S: Cavendishia spp. 2.0 2 Morphospecies E, F, G, J, K, L, and O were all found on an average bill length over 3.2cm (refer to table above) and the three (G, J, K) that were identified had flowers that ranged from 3 to 8 cm in length (Table 1). S has a flower that is 2.3 cm long and was on birds with an average bill length of 2.0cm. So in t his case longer billed birds were feeding on flowers with longer corollas and shorter billed on shorter corollas. Discussion The analyses of data from Bleiweiss (1999) revealed that as body size increases so does bill length. The significance of these results is that longer billed hummingbirds feed on
uyma 1983). So, if a bird is traveling greater distances for greater rewards then a larger body size (longer wings) would be advantageous to support these travels. This relationship between body size or wing length and proboscis length also exists in other groups such as Sphingid moths. In this case, wing length and body size are closely correlated with proboscis length, and furthermore correlated with the amount of time a moth hover (Bullock 1983). According to the results of the correlation analyses of da ta by Feinsinger (1986), hold up in regression test, because there may have been too few data. But, the current field study did revealed a strong significance betwee n increasing bill length and ri chness. These results appear to contradict the hypothesis that a longer corolla tube will have fewer, more specialized pollinators in order to conceal their nectar from more generalist pollinators (Fenster, 1991). However, in Monteverde where the proportion of hummingbird pollinated plants increases on a elevational gradient (Fraser, 2003), an increasing number of pollen species on longer billed birds may simply reflect an increasing abundance of long corolla plants. This is b ecause as elevation increases other pollinator activity, such as insects, is limited due to cooler temperatures (Stiles 1989). Plants possibly are relying more on hummingbirds for pollination. This reasoning may also justify significant differences in loca tion of pollen on the birds. Since these longer, more specialized flowers are producing higher quality nectar, and therefore using more energy in its production, it would be more effective to specialize the pollen placement. By doing so, the chance of that pollen is delivered to a conspecific increases (Futuyma, 1983). Another significant result here is that females carried a considerably greater pollen richness then males. According to Stiles (1989) most hummingbirds are very aggressive, males hold regular feeding territory and defend them against all other hummingbirds regardless of sex. On the other hand, females of many species visit widely scattered flowers on regular foraging routes. If females are traveling greater distances, chances are that they wi l l encounter a more diverse ran ge of flower species, and therefore will carry a more diverse pollen load. Finally, this study proves that longer billed birds visit longer corolla flowers. Not only do longer corolla flowers provide a richer nectar source, th ey also reduce competition. Short corolla flowers are rarely pollinated exclusively by hummingbirds, and therefore, their hummingbird pollinators are forced to compete for resources with other animals (e.g. insects) as well as other hummingbirds (Fenster, 1991). Further studies could look at larger sample sizes to get a more even distribution of long versus short billed hummingbirds. Elevation differences could be looked at to see if longer or shorter billed birds are more common at lower elevation. Finally male and female relationships could be further be explored over a range of species in relation to bill length.
Acknowledgements: I would like to thank my mother Dr. Alan!!! My Best friend Andrew You know who you possible. Joe (Metrosexual) Northrops this paper represents our love. Finally I would like to thank Princess Sarah, for being a Princess!
Literature Cited: Ble iweiss, R. 1999. Joint effects of feeding and breeding behavior on trophic dimorphism in hummingbirds. Proc. R. Soc. Lond. B 266: p. 2491 2497. Bullock, S. H., Pescador, A. 1983. Wing and proboscis dimensions in a Sphingid fauna from Western Mexico. Biothropica: 15(4): p. 292 294. Feinsinger, K., Murray, G., Busby, W. H, Beach, J., Linhart, Y. B. 1987. Disturbance, pollinator predictability, and pollination success among Costa Rican cloud forest plants. Ecology: 68(5): p. 1294 1305. Feinsinger, K., Mu rray, G., Kinsman, S., Busby, W. H. 1986. Floral neighborhood and pollination success in four hummingbird pollinated cloud forest plant species. Ecology: 67(2): p. 449 463. Fenster, C.B. 1991. Selection on floral morphology by hummingbirds. Biotroica: 23: p. 98 101. Futuyma, D.J., Slatkin, M. 1983. Coevolution. Sinauer Associates Inc.: Sunderland, Massachusetts: p. 301 306. Fraser, S. 2003. Flower color and shape variation on an elevational gradient. Tropical Ecology and Conservation: Monteverde, Costa Rica : Council on International Education and Exchange: New York. Stiles, G.F., Skutch, A.F. 1989. A guide to the birds of Costa Rica. Comstock Publishing Associates: Ithaca, New York: p. 208 209. Zuchowski, W. 1996. Common flowering plants of the Monteverde Cloud Forest Preserve. Tropical Science Center. San Jose", Costa Rica.
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Hummingbird Size, Pollen Load and Pollination Efficiency
Digitized by MVI
Pollinators are an important selective agent and play a role in the evolution of certain
floral characteristics (Fenster, 1991). This is often the case with flower corollas, which
have closely coevolved with the length and curvature of the bill or tongue of its
pollinators (Stiles 1989) The purpose of this study was to determine the specificity of the
coevolution between hummingbirds as pollinators and the species on which they forage. I
also hope to examine the bill length- body size relationship, pollen loads and their
placements. I hypothesize that short-billed hummingbirds will carry pollen from plant
species with short corollas, and long-billed hummingbirds will carry pollen from plant
species with longer corollas, even though they are capable of getting nectar from shorter
corolla flowers. Hummingbirds for this study were collected between October 20 and
November 14, 2003 around the Estacin Biolgica Monteverde, Puntarenas, Costa Rica.
When number of pollen species was plotted against bill length in a simple regression
(Fig. 6), the relationship turned out to be significant (P = .0021). As bill length increases
the number of pollen species found on a bird also increased. Species richness on the bill
was significantly different then on the chest with a P-value of 0.0324 and bill vs. total
species of pollen was also found to be significant (P = 0.0015) (Fig. 8). Chest and bill
vs. total were also showed a significant difference in species richness, both having Pvalues
of < 0.0001. So the females are carrying significantly more pollen species than
males. When looking at body parts the greatest amount of pollen species is being carried on
the bill, followed by the head and then chest. Females were determined to carry greater
pollen loads then male due to male territorial behavior. Also, long-billed humming birds
feed mainly on long corolla flowers.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--Monteverde
Costa Rica--Puntarenas--Zona de Monteverde--Monteverde
Tropical Ecology Fall 2003
Ecologa Tropical Otoo 2003
t Monteverde Institute : Tropical Ecology