Exploring Toyon Trees and Birds

I have put together a multi-disciplinary lesson plan that can be extended almost indefinitely. My lesson was inspired by a scientific article concerning the cyanide in Toyon berries, and I went from there to an article in Bay Nature Magazine, which is reproduced below. The basic article is about which birds eat Toyon berries, but I have included suggested activities throughout the article that incorporate nature study, bird anatomy, ethnobotany, math and measurement, critical thinking.  No special materials are needed, the lesson gets kids outdoors and involves them in research and artwork. *See upcoming lesson: How Native Americans used California Plants

cedar waxwing eating berry

The article is black, my activities are in blue italics. Activities are suitable for many different grade levels. I hope you enjoy it. 

Ask The Naturalist: How Important Are Red Toyon Berries To the Winter Food Chain?

From Bay Nature, by Alison Hawkes and Alan Kaplan

December 22, 2016

The bright red berries of the toyon plant make this native perennial shrub a festive feature of the winter season in California. These leafy bushes are common in chaparral and oak woodland habitats, but they are also well loved garden plants given their drought-tolerance and attractiveness for much of the year as the summer bloom of small, white flowers turns to an abundance of red berries in the fall, carrying well over into the winter months. Of course, we’re not the only ones who love those berries.toyon berries

Activities:

Look up a picture of Toyon. Do you have this plant in your yard or neighborhood? It is very common in the Capay Valley.

Go on a walk to see if you can find a Toyon. Draw it, including leaves, stems, berries. Use colors. *See upcoming lesson: completing a science drawing

If you find a Toyon tree, what stage is it in? Are there berries, flowers, or neither? 

Are there any animals/insects feeding on the leaves, flowers, or berries? See what you find. Can you identify them? Make a list next to your Toyon drawing.

Bay Nature put this question to Alan Kaplan, a retired East Bay Regional Park District naturalist and birder: How important are toyon berries to the winter food chain? 

Wintering birds in our area often depend on the fruits of native and exotic (ornamental) berry plants to sustain them. Three common fruit eaters are American robin, cedar waxwing, and hermit thrush.

cedar waxwing

Activities: 

Look up photos of these birds online. Can you find these birds  in your yard? 

What does “ornamental” mean? Can you find both ornamental and native plants in your yard? How were they planted? By hand, or did they arrive some other way? 

In the 1970s, ornithologist Stephen Bailey looked at how these birds use berries in winter and how they interact with each other. (He was a graduate student at UC Berkeley at the time.) He found that toyon (Heteromeles arbutifolia) was the most important source of berries for robins, thrushes and waxwings, though they also make use of other berry plants on the university’s campus, such as cotoneaster, privet, pyracantha, holly and juniper.

Low in protein and calories, berries offer limited nutritional value, especially to small birds who need to consume their body weight in food each day to survive the winter. For example, a bird would need to consume 3 ounces of (dried) toyon berries to get the same 331 calories that could be had with only 2 ounces of sunflower seeds. Nevertheless, if you’re a wild bird you take what you can get!

Activities:

How do protein and calories contribute to nutrition? Why are each important? What foods do you eat that are high in protein or high in calories? 

Use a measuring cup to discover the amounts for 3 ounces and 2 ounces. A scale could also be used. 

Which food (toyon berries or sunflower seeds) gives the most calories per serving? Do you eat either of these foods yourself? Ripe Toyon berries were used by Native Americans for food, beverages and medicine. *See coming lesson: making a calorimeter

Bailey found that he could learn a lot about bird behavior by watching them tackle a berried bush. Each of the three species he studied — American robin, cedar waxwing, and hermit thrush — had a different strategy of getting its fill. Each competed with the others and none could exclude the others altogether.

The large American robin throws its weight around, dominating the other birds when defending a rich bush of berries against individual hermit thrushes or a small number of cedar waxwings. Cedar waxwings, in turn, overwhelm the defense of robins with their large numbers, making up with flocking what they lack in fierceness.

Both the robins and waxwings prefer to perch and pluck at berries within reach, and spend about 16 minutes at a time doing that. Robins take five berries during that time, and cedar waxwings take three. A robin might eat its weight in berries in a day (about 3 ounces), filling and emptying its crop three times per hour. These birds must eat so much because the nutrient content of their food is low, and they digest it very rapidly (so less of the nutrients are absorbed).

bird anatomy

Activities:

What is a “crop”? Look up the anatomy of a bird. How does a crop help a bird digest food? Do other animals have crops? *see upcoming lesson: Earthworm habits and anatomy

Use a timer or clock to discover how long 16 minutes takes to pass. If robins eat 5 berries in 16 minutes, approximately how many minutes does it take to eat one berry? If cedar waxwings eat 3 berries in 16 minutes, how many minutes does it take to eat one berry? Which bird eats the fastest? Why do you think different birds eat at different rates? *See upcoming lesson: Pendulums and time

Think about the phrase “they digest (their food) very rapidly – so less of the nutrients are absorbed.” How and why is food digested in your own body? Are some foods digested more quickly than others? Consider simple sugars and more complex sugars such as contained in potatoes. Where are nutrients absorbed into our bodies? Stomach, intestines? *See upcoming lesson: Walk through the human digestive system.

human digestive system

Hermit thrushes skulk around very carefully and zip in and out of a bush, bagging one berry at a time from under the nose (beak) of the dominant robin. Robins and thrushes will also take fallen berries from the ground (waxwings will not), but the hermit thrush remains a sneak thief most of the time. It only gets about two berries per bout of feeding, but it, too, eats its weight in berries each day. The thrush would prefer to stay deep in a berry bush, eating as inconspicuously as possible. Some of the robins and thrushes do spend the entire winter in a single bush if it is rich enough in berries.

As the season progresses and food becomes scarcer, robins become more territorial and aggressive, and cedar waxwing flocks become larger in response.

american robin

Do plantings of toyon and exotic berry-bearers make a difference to overwintering birds? Yes! Populations of overwintering fruit eaters are more stable and more reliably found because there is a regular supply of berries. Fruit put out at bird feeders and ornamental plantings around homes have helped the northern mockingbird expand its winter range in the West (the seed-eating cardinal has profited similarly in the East). Shrubs, planted as ornamentals around homes, can be easily defended from other birds. The larger and more conspicuous the planting, the greater its chances of attracting cedar waxwings and American Robins.

And that is exactly why the plant produces its attractive berries in the first place (usually reddish and blackish colors predominate, though we don’t know why). The toyon goes so far as to have the short stems (pedicels) bearing the berries turn bright red, to be extra attractive to fruit-eaters and ensure that all the berries are eaten.

Activites:

Did your drawing of the Toyon include colors of the berries and also the stems? 

Plants don’t have “intention”, but they do reproduce better by attracting animals. Why would a plant find it advantageous to attract birds to its berries? *See upcoming lesson: Seeds and their dispersal

Plants can also attract animals to their flowers. Why would it be beneficial for plants to attract animals to their flowers? An entire lesson can be done on this topic! *See upcoming lesson: How plants use flowers to attract pollinators

Berry eaters digest the nutritious coating and excrete the seed intact, helping it with a bit of fertilizer for a good start! Seeds are excreted away from the parent plant, reducing competition for water and sunlight.

For a lesson in food chain dynamics, go ahead and observe a local berry bush this winter. Note the abundance of fruit as the season begins, and then watch the change in the number of berries through the winter. You may be lucky to see a flock of cedar waxwings settling down to a mid-winter feast as the resident American robin tries in vain to beat them back. And, lurking nearby, ever ready to dart out for some really fast food, could be a hermit thrush.

More Information from the Los  Angeles Times:

The berries of Toyon are actually poisonous to birds if eaten unripe. This is because there are two compounds in the berries that combine to form cyanide if the berries are crushed while green. When birds peck at green berries, cyanide gas is formed and birds leave them alone. It is only when the berries are fully ripe and red, that cyanide is naturally removed and birds can safely eat them.

Activities:

What would be the advantage to Toyon to produce cyanide while the seeds are unripe?

What is the difference between liquid and gas? How would the bird most likely sense the cyanide, taste or smell? *See upcoming lessons on states of matter, and smell testing.

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