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Western bluebirds actually kiss the mistletoe

I have never understood the tradition of kissing under the mistletoe. Mistletoe is a parasite. OK, technically it’s a hemiparasite, meaning that it’s not totally dependent upon its host for food. It has green leaves that allow it to make much of its own food, but its haustoria (think roots but not quite) penetrate the tissues of the host tree and steal water, minerals and additional food. A heavy infestation can weaken or even kill a tree.

So, what is romantic about a parasite? The story that has been related to me is that oaks and other trees infected by mistletoe are deciduous. In winter, the mistletoe remains green on an otherwise barren tree and often blooms throughout the winter months. It is the promise of spring and a symbol of fertility. That sounds a bit better than the parasite story.

Now enter western bluebirds. Who isn’t impressed at the sight of a bright male bluebird landing close seemingly unconcerned with your presence? We are fortunate to have a large, healthy population of bluebirds in the Rogue Valley. Western bluebirds have declined in other areas. They have been reduced to a few pairs in the Willamette Valley due mostly to competition from introduced starlings for nesting sites and the loss of oak habitat. Eastern bluebirds have also suffered serious declines.

For much of the year, bluebirds are ground foragers. Those that study bird behavior refer to them as “pouncers.” They wait patiently on a perch until they spy a grasshopper or caterpillar crawling on the ground and then pounce on it.

In winter, grasshoppers and caterpillars are few. Bluebirds turn their attention to fruit. Fruit may not be plentiful, but it is more abundant than caterpillars.

Besides dried Oregon grapes and poison oak berries, mistletoe fruits are plump and a great food source. Family groups of bluebirds visit mistletoe clumps throughout the winter. The bright blue males and even the more somber females add a spot of color to the drab winter landscape.

Now mistletoe is tricky. The fruit is nutritious, but the seeds are sticky. After feasting on the berries, the bluebird rubs its beak on its perch do dislodge the sticky seeds, usually in a nearby tree. The mistletoe has just found a new host. Similarly, seeds that pass through the digestive track of a bluebird are still sticky and are deposited on new hosts. So much for romance. Maybe it is better to keep biologists away from folklore.

While bluebirds have a special fondness for mistletoe berries, they are not the only villain in this story. Others include robins, Townsend’s solitaires, cedar waxwings and even starlings. They all love a good meal of mistletoe berries and disperse their seeds as well.

There are other mistletoes in the region, dwarf mistletoes. These infect conifers and have a different way of dispersing their seeds. The dwarf mistletoe explosively launches its sticky seeds at speeds of up to 50 miles per hour, and if a seed lands on a suitable host, it starts a new infection. Foresters have no affection for dwarf mistletoe.

I don’t know whether oaks live in fear of bluebirds, but to my mind a family of confiding bluebirds in my yard on a drab winter day can be forgiven.

Stewart Janes is a biology professor, emeritus, at Southern Oregon University. He can be reached at janes@sou.edu.

A mountain bluebird eats a giant mistletoe berry in an ash tree in Sedona, Arizona. Bluebirds, and many other types of birds, rely on mistletoe berries for sustenance. As a result, they also help distribute the mistletoe seeds. Photo by Todd Esque, USGS Western Ecological Research Center