Birds and Berries

Do animals exploit fleshy fruits for food or do plants exploit animals to disperse their seeds? The topic came up in one of my classes recently, and for at least a few college students, the thought of a plant exploiting an animal was a foreign concept. Actually the plants and animals are both exploiting each other. It is what biologists call coevolution. A good example is “birds and berries.” Now let’s try to look at it from a plant perspective.

Many of our native plants produce brightly colored fleshy and sugary fruits. Many are familiar plants, such as chokecherry, wild strawberry and raspberry, hawthorn, and Juneberry. Brightly colored and sugar-loaded fruit is the price some plants must pay to have their seeds dispersed. But that is just the beginning. Many of these seeds must be scarified before they can germinate. Anything that ruptures the seed coat is scarification, and for these seeds it is the bird’s strong digestive juices.

Some birds will ingest the seed containing fruits, digest the fruit, and regurgitate the now scarified seeds. Typically, however, the seeds will make the miraculous journey from one end of the bird to the other end, scarified, but still intact.

What a trip! There is more suspense and intrigue in this trip than all the Indiana Jones movies combined. If the seed passes too quickly through the digestive system the seed will not get very far away or be scarified. Unless something else happens to rupture the seed coat it may not germinate. If the seed stays in there too long, it could be digested, and of course that would be a complete failure.

It’s Goldilocks all over again. Everything has to be “just right!” The seed coat can not be too tough or too weak, digestive juices can not be too strong or too weak, and of course the time the seed spends getting assaulted by all those digestive juices must be just right. There is an amazing array of factors that must work out correctly for these plants to disperse their seeds to new areas and produce the next generation.

So give some thought to all that is happening the next time you see a few birds working the berries near your home. They are doing important plant work. Like they say, “Bloom where you are planted,” and of course a little extra fertilizer surrounding the seed certainly helps.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.