Birds collect nectar as a source of energy. Sugar is a large component of nectar and is used in hummingbird metabolism for the production of energy. Flowers produce nectar as a reward for those organisms that are potential pollinators. It is a win-win situation for both the bird and the flower. The bird receives food, and the flower receives and releases pollen.
Using simple extraction techniques nectar volume, sugar concentration and caloric reward can be easily determined. Students can then apply this data to the metabolic demands of the ruby-throated hummingbird.
Groups should be supplied with at least one micro-pipet, one millimeter ruler, one refractometer and one species of plant.
Micro-pipets are used to sample nectar for two reasons. First the pipets are calibrated so that nectar volume can be determined. Second, the narrow pipet opening allows most nectars to flow into the tube via capillary action. The tube should be held by the end with the colored (orange) band, and the 10 microliter calibration is marked with a thin black line.
Students may need to dissect a cuple of flowers to locate the source of the nectar before attempting to probe the flower. Once the nectar is located the pipet tip is used to probe the flower for nectar. Use the tip away from the colored band to probe the flower. Capillary action will draw the nectar into the thin tube. Students should attempt to collect nectar in a non-destructive manner.
The nectar volume may be determined once all nectar has been extracted from the flower. Examine the pipet. The 10 microliter line is approximately two-thirds of the distance from the pipet tip. Volumes less than 10 microliters can be determined using the following relationship.
Sugar refractometers measure the refractive index of a solution. This index is a property of the molarity of the sugar in the solution and how the solution polarizes light. The refractometer we will use measures concentrations of nectar that are 0-50% sugar (g of sucrose / g of solution). Most nectars are secreted at a concentration lower than 50%.
This concentration should be converted to a concentration(mg/ml) that we can use to determine the amount of sugar (mg) in the nectar sample. An example is shown below.
If you do not have access to a refractomoter, the nectar collected from these species of plants has an average sugar concentration of 20%. You may use this value in your calculations
| % Sucrose | mg/ml | % Sucrose | mg/ml |
|---|---|---|---|
| 2 | 20.1 | 26 | 288.1 |
| 4 | 40.6 | 28 | 312.9 |
| 6 | 61.3 | 30 | 338.1 |
| 8 | 82.4 | 32 | 363.7 |
| 10 | 103.8 | 34 | 389.8 |
| 12 | 125.6 | 36 | 416.2 |
| 14 | 147.7 | 38 | 443.2 |
| 16 | 170.2 | 40 | 470.6 |
| 18 | 193.0 | 42 | 498.4 |
| 20 | 216.2 | 44 | 526.8 |
| 22 | 239.8 | 46 | 555.6 |
| 24 | 263.8 | 48 | 584.9 |
This table is modified from Kearns and Inouye, 1993.
Simply multiply the amount of sugar per nectar sample by 4 to determine the caloric reward per flower. If 1g of carbohydrate = 4 Kilocalories of energy, then 1mg of carbohydrate = 4 calories of energy.
Students should be assigned to work in small groups. Each group should be assigned a different flowering plant. Students should work together to extract nectar, determine nectar volume, caluclate amount of sugar and caloric reward. All data should be recorded in the data table provided. Averages of appropriate columns should be calculated.
| Flower Number | Nectar Collected | Volume of Nectar | Nectar Concentration | Amount of Sugar | Caloric Reward |
|---|---|---|---|---|---|
| Example | 25mm | 3.3microliters | 26% | 0.95 | 3.8 calories |
| 1 | 2 | 3 | several more samples may be taken | ||
| Average |
Students can now compare the production of nectar in several species of flowers.
Using the following chart answer questions 1-6.
Investigate whether hummingbirds will forage a specific color of flower in order to locate nectar.
Make 6 "flowers" from film canisters and cardboard. Cut out 6 pieces of cardboard in a circular shape paint then different colors: red, pink, blue, green, purple and yellow, and paste them to the top of 6 film canisters. Poke a small hole in the center of the "flowers." Mix a 20% sugar solution (one part sugar to 4 parts water) and fill the canisters. Place the canisters into floral foam so they do not leak. Assign groups of 2 students to record the number of probes per flower color. Recording time should be 15 minutes. After at least 5 sets of data are collected, total number of probes can be counted and discussed. If you are working with an advanced group you may wish to conduct a chi square test to determine whether your results are statistically significant. Sample data
Investigate whether hummingbirds prefer specific sucrose concentrations.
In 4 hummingbird feeders mix four different sucrose concentrations:10%, 20%, 30%, 40% . To mix a 10% solution simply mix one parts sugar to 9 parts water. To mix a 20% solution mix 2 parts sugar to 8 parts water. Assign students in groups of 2 to record the number of probes per concentration. After at least 5 sets of data are collected, total number of probes can be counted and discussed. If you are working with an advanced group you may wish to conduct a chi square test to determine whether your results are statistically significant. Sample data
Operation RubyThroat
The Hummingbird Society
Fisher Scientific
Refractometers (~$300)
Bellingham and Stanley
5815 Live Oak Parkway
Suite 2C
Norcross, GA 30093