Point Reyes Bird Observatory, Observer 108

FOCUS

Deadly Eucalyptus

Eucalyptus specialists "down under" are larger and better equipped than North American species to forage in flowering trees. Comparisons of bill lenths between Euclyptus specialists and some North American birds.
NOTE: Bill lengths given in inches LEFT (top to bottom): Tasmania's Yellow Wattlebird, Australia's New Holland Honeyeater, and Eastern Spinebill.
RIGHT (top to bottom): Yellow-rumped Warbler, Ruby-crowned Kinglet, and Anna's Hummingbird.

By Rich Stallcup
All drawings by Kieth Hansen. Copyright 1997.
Jeez! What a tree! It's late December in northern California, but the list of birds foraging in the blossoms makes us feel like we're in Manzanillo. In addition to many individuals of our regular winterers - 20 Anna's Hummingbirds, 20 Audubons and 3 Orange-crowned warblers, 10 Ruby-crowned Kinglets, and a few starlings - there are two kinds of orioles, a Palm and a Nashville warbler, a Warbling Vireo, and a Summer Tanager! It's a Christmas Bird Count compiler's dream: six rare species, all in one tree.

But... hmmm... something isn't natural here.

On the ground beneath the tree, we find a dead Ruby-crowned Kinglet, its facial feathers matted flat from black, tar-like pitch. Through a hand lens I can see that its nostrils are sealed shut. This little bird has suffocated as a result of its attraction to an exotic plant. I wonder out loud if the same fate becomes all the black-faced insectivores we see foraging in flowering eucalyptus. Years ago I found a dead hummingbird with black tar covering its bill and wondered why. It was in a cemetery in Oakland - under eucalyptus trees.

Exotic plants

Several species of eucalyptus trees were imported to North America from Down Under in the 1800s, for timber, windbreaks, and ornamentation. Eucalyptus globulus, the blue gum, is native to Tasmania and has become the most common large "euc" in California. During our winter (October to March), many of them produce abundant flowers, which in turn attract insects that invite these special sorts of birds. Without the presence of the trees, many of these birds would migrate, as they should, into the American tropics.

Some exotic plants, like gorse, Scotch and French brooms, and pampas grass, are invasive and, if allowed their own way, will displace any and all native plants in their path. Eucalyptus do not spread as quickly, but their acrid, aromatic leaf litter precludes an understory of other kinds of vegetation. Except for providing occasional nest sites for Great Horned Owls and Red-shouldered Hawks, non-blooming "eucs" do not provide much food or shelter for native birds or other animals.

They are what they eat

Birds have evolved body types, especially bill shapes and lengths, in accordance with their environment, their feeding strategies, and the plants in which they forage. Honeyeaters and other species of eucalyptus specialists indigenous to Tasmania and Australia have long, curved bills: they can probe the flowers without involving their feathers or nostrils. Leaf-gleaners like North American kinglets, vireos, and wood warblers, have short straight bills. To seek insects or nectar within eucalypus blossoms, they must insert much of their heads, thus glopping up their faces. There are no native North American plants that invite this type of harm.

The long and ongoing arguments over eucalyptus "management" seldom touch on wildlife issues but instead are more people-oriented. Some say the trees have been here so long that they are naturalized citizens, or argue how beautiful they are to the human eye. The other side calls them unnatural or feral immigrants and fire hazards.

Native wildlife finds little use for eucalyptus except for those trees in bloom, and many birds that swarm to flowering "eucs" may die as a result of this connection. Non-blooming "eucs" cause areas of ecological emptiness that could otherwise be viable habitat if planted with native trees like oaks or pines. From a point of view that would favor the health and prosperity of native North American plants and animals, especially birds, eucalyptus trees (particularly those that bloom from October to February) should be removed.



Return to Observer's Table of Contents

Return to PRBO's Front Page





Point Reyes Bird Observatory
Copyright 1997
PRBO at prbo dot org