Participants: Dale Mast, Noel Nelson, Suzanne McClung, Mark Lyke, Kathi Jouvenat, Christa Lundberg

Site: Las Cruces

Key Words: Hummingbirds, time of day, species identification, number of visits, color of flower

Introduction:
Breeding and nesting in Costa Rican hummingbirds takes place roughly from December/January through August. This coincides with Heliconia blooming, which is their main source of nectar (Stiles, 1983). During this time, hummingbirds also feed on other nectar producing plants. Hummingbirds and many plants have developed a mutualistic relationship: plants attract hummingbirds with nectar in order to cross-pollinate. Flowers vary their nectar availability throughout the season and time of day in order to attract hummingbirds (Schwendener, 1997).

Hummingbird feeding behaviors correlate to the availability of nectar (Fishman, 1995). Behaviors such as perching without feeding on the plant and chasing off other birds are considered to be defensive protection of the nectar source (Schwendener, 1997). Rufous-tailed hummingbirds (A. tzacatl) are highly aggressive and territorial. The males are emancipated from the females in parental caretaking of the nestlings. Either males or females will defend a plant from other birds (Stiles, 1983).

As forests become fragmented, corridors for hummingbirds must include a variety of nectar-producing flowering plants. Luckily, hummingbirds are a versatile edge species and tolerate the fragmented landscapes fairly well (Snow, 1999). Hummingbird mutualistic plants have evolved colors and structures, including variable nectar production, in order to attract hummingbirds (Schultz, 1996). The Wilson Botanical Garden was cultivated on the edge of a secondary forest fragment as a soft edge, and should continue to be organized to attract many hummingbird species (Shapiro, 1996). We wondered if different areas of the Wilson Botanical Garden are optimally arranged by color to attract hummingbirds at constant and specific times throughout the day. Hummingbirds are known to be attracted more to red and yellow colors (Shih, 1997). We investigated three plant species, each having a different-colored flower, and located in a different part of the Wilson Botanical Garden. Would there be a difference in hummingbird activity on the different plant species? We expect that all three different-colored flowers will attract hummingbirds, although previous research supports the expectation that the red flowers will attract a higher number of hummingbird visits.

Methods:
We began by surveying the Wilson Garden at Las Cruces Biological Research Station for trees and bushes where there was hummingbird activity. We selected three trees of different species and flower color in different locations. Identification of the trees was made using signs in the garden and Gentry (1996). The three trees were as follows:

Results:
The data are summarized in Table 1. We collected data over a two day period. The data were recorded between 7-8 AM, 1-2 PM, 7-8 PM. Each team of two recorded the perching and bill probes at their site during a one hour period of time. Each team rotated sites taking data twice at each site. Our last time block was canceled due to a scheduled speaker. That still gave us five sets of data per site.

The red flowers (Erythrina) resulted in 37 perching and 496 probes. The mean was 7.4 for perching and 99.2 for bill probes. The standard deviation was 3.5 for perching and 52.6 for bill probes. The number of red flowers was 440 and produced a rate per blossom per hour of 0.23.

The white flowers (Costus stenophyllus) resulted in 73 perching and 59 probes. The standard deviation was 14.6 for perching and 11.8 for bill probes. The number of white flowers was 20 and produced a rate per blossom per hour of 0.59.

The lavender flowers (Bouganvillea) resulted in 9 perching and 17 probes. The mean was 14.6 for perching and 11.8 for bill probes. The standard deviation was 2.2 for perching and 4.5 for bill probes. The number of lavender flowers was 650 and produced a rate per blossom per hour of 0.005

As predicted by our hypothesis, we did have more visits to the red flowers but the rate per blossom per hour was smaller than for the white flowers. The mean was 1.8 for perching and 3.4 for bill probes. We had a greater number of hummingbirds perching on the branches of the white flowers. The hypothesis was not supported by our data.

Discussion:
Our original intent was to observe hummingbird visits to heliconia plants in three different environments: secondary forest, the Wilson Botanical Garden, and along the roadside outside of Las Cruces Biological Station to determine the effects of human activity on hummingbird behavior. Our preliminary observation to determine the feasibility of this study resulted in our revising our hypothesis. There were no hummingbirds around the heliconia in the Garden. When we had arrived at our new hypothesis, we again conducted a preliminary survey and selected three sites within the Garden, one with a red-flowering plant , one with a white-flowering plant, and one with a lavender-flowering plant.

The new hypothesis contained more variables, which made it more difficult to determine the causes of the hummingbird behaviors we observed. We were unable to determine whether the variation in the number of visits was due to the time of day or the weather conditions, which ranged from clear to overcast to rainy. Neither could we determine whether the hummingbirds observed were attracted to the color of the flowers or the nutritional value of the nectar each contained. Since we only had one sample of each species that we observed, our results may be difficult to replicate. Further studies would include:

1. A larger sampling (min. 3) of each species to provide more reliability in our findings
2. A broader sampling (min. 3)of same-colored flowers of different speciesto determine whether color or other qualities are the determining factors
3. Examination of the nutritional value of the nectar of flowers of each species
4. Use of spectrophotometer to determine the true color of flowers, since hummingbirds and their observers may not perceive colors in the same way

Finally, it proved much more difficult to identify the species of the visiting hummingbirds due to several factors: the lighting, the speed at which they zip about, the weather conditions, and the similarity in appearance of many of the species.

Acknowledgements:

Thanks go to Tom Langen for his help and consultation on our project. Likewise, David Silverberg consulted with us on our project. Also, we would like to thank Rodolfo Quiros for the use of his slides.

Literature Cited:

Program Coursebook,1996.

Appendix 1: The Essential Question – Classroom Applications

Observe a living animal in its environment outside if possible. If not, use earthworms, mealworms, goldfish, jumping beans, sowbugs. If students need suggestions, brainstorm on what animals they might see outside around the school before going out.

• Select one animal
• Observe for 40-60 minutes
• Formulate 3-5 questions
• Develop an investigation based on one of your questions

• TITLE
• PURPOSE
• PROCEDURE (teacher checks this before students continue with the investigation)
• DATA COLLECTION
• DISCUSSION OF RESULTS
• EXTENSIONS:
• What went well?
• What problems did you have?
• Three questions generated from the investigation
• Identify and research potential environmental changes to the organism and how it would change the ecosystem
• REFERENCES USED/CITED