By Elizabeth Pennisi
Northern Arizona Audubon Society Newsletter Nov/Dec 2015
Humans use it hoping for a kiss. A surprising number of bird species use it as a food source and a nesting site. In fact, the name came from people who observed that it often would grow in places where birds had left their droppings. “Mistel” is the Anglo-Saxon word for “dung,” and “tan” is the word for “Twig.” Thus the birds and this parasitic plant have a co-dependency. Birds eat the berries and their droppings then distribute the seeds.
Scientists studying this relationship have observed that forest with a high abundance of dwarf mistletoe will have more birds and a greater variety of bird species. Mistletoe will eventually kill its host plant leaving a snag that can be used by cavity nesting birds. One study documented a least three times as many cavity-nesting birds live in forest with abundant mistletoes compared to forests without.
Birds that take advantage of mistletoe include grouse, Mourning Doves, bluebirds, Evening Grosbeaks, robins, and pigeons. Naturalist and writer John Muir noted American Robins eating mistletoe in the mountains of California in the late 1890’s. Wrote Muir: “I found most of the robins cowering on the lee side of the larger branches of trees, where the snow could not fall on them, while two or three of the more venturesome were making desperate efforts to get at the mistletoe berries by clinging to the underside of the snow-covered masses, back downward, something like woodpeckers.”
A dense clump of mistletoe is called a witch’s broom and provides good cover for nests. Northern and Mexican Spotted Owls and other raptors prefer these as nesting sites. Nests of Cooper’s Hawks, Great Gray Owls, Long-eared Owls, Northern Goshawks and Sharp-shinned Hawks have been found in mistletoe clumps. Likewise, some migratory birds nest in witches’ broom—Gray Jays, Red Crossbills, House Wrens, Mourning Doves, Pygmy Nuthatches, chickadees, Western Tanagers, Chipping Sparrows, Hermit Thrushes, Cassin’s Finches, and Pine Siskins.
Birders would be wise to give a close look at mistletoe clumps to see what they might be hiding.