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All Is Not Merry for Intoxicated Birds

Arkansas Natural Heritage Commission - Tuesday, February 27, 2018

Recently, several concerned Arkansas citizens have reported urban birds, specifically cedar waxwings (Bombycilla cedrorum), acting strangely. The birds have been found lying on the ground and in the open. They don’t try to fly away when approached. Why are the birds acting like this?

Turns out, these reports aren’t unusual for this time of year. As the weather begins to warm in late winter, berry-eating birds gorge on berries that are currently plentiful in order to fuel up before migrating north for the summer. As the weather begins to increase closer to the beginning of spring, the berries heat up too. The sugars in the berries ferment and the birds, having consumed large amounts of the berries, become intoxicated.

Scientists call this “fermentation toxicity” and it is common in cedar waxwings, robins (Turdus migratorius), and other berry-consuming birds. Birds under the influence may lie on the ground, smash into windows, or fly into other objects. Unfortunately, not all is merry with birds eating these berries.

The most common form of intoxication in birds in urban areas during this time of year is cyanogenesis, where berries of certain plants produce more concentrated amounts of hydrogen cyanide, which can be fatal to birds and even larger animals like dogs. Cyanogenesis is more common in urban areas due to a higher frequency of non-native ornamentals that produce more toxic berries, with the biggest culprit being nandina (Nandina domestica). Nandina is a prevalent urban ornamental evergreen plant, commonly called sacred bamboo or heavenly bamboo. This native to Japan, China, and India is often planted in the southern and southeastern U.S. because it can tolerate a wide range of soil and light conditions. Nandinas produce large quantities of bright red, showy berries in the fall that last throughout the winter.

Birds that eat only a few nandina berries may suffer lower intensity of cyanide poisoning and appear drunk, even to the point of being unable to fly or hop around. Those birds that consume high amounts of the berries are subject to hemorrhaging of internal organs and often die within an hour. Cedar waxwings, because of their tendency to overly gorge at berry bushes, are very susceptible to cyanide poisoning from eating nandina berries [See Feeding Behavior-Related Toxicity due to Nandina domestica in Cedar Waxwings (Bombycilla cedrorum)].

Why Do Plants Produce Berries That Include a Toxin?

Plants produce berries as an adaptation to entice animals to eat the berries. The animals will later disperse the seeds (within the berries) when they defecate. Why would a plant produce berries that include a toxin which could deter the consumption, and thus dispersal, of the seeds? It appears that this is a strategy that some plants, shaped by natural selection, use to determine when their seeds are dispersed. For example, berries lacking toxins are consumed first, giving those plants the advantage of getting seeds spread more quickly across the landscape. Plants that produce toxic berries may have the advantage of avoiding environmental conditions (heavy rains that might bury the seeds too deep, animals that might eat the seeds, etc.) that could prevent the seeds from germinating.

Many plants native to Arkansas have toxins in their berries, but the berries of the non-native nandina are often lethally poisonous. Native birds and other native animals lack the physical and behavioral adaptations to deal with this toxicity because it is something very new in their evolutionary history (since the plant is introduced from another continent). We can help by planting native plants and by avoiding the use of nandina.

What Should I Do if I See an Intoxicated Bird?

Experts recommend that you leave the bird alone, unless you think it might be attacked by a predator. If so, they advise that you gently coax the bird to a quiet, covered area to “sleep it off.” Remember to be careful, because the birds may be sleepy, but they will still bite – use a glove or other barrier to protect yourself. If the bird does not recover within a few hours or you are worried that the bird has injured itself, contact a local wildlife rehabilitator for further instructions.

 

Photos: 

Top left -- Cedar waxwing (Bombycilla cedrorum) eating a berry, photo by MDC staff, courtesy of Missouri Department of Conservation

Far right -- Cedar waxwing (Bombycilla cedrorum), photo courtesy USDA Forest Service

Bottom image -- Cedar waxwing (Bombycilla cedrorum), photo courtesy USDA Forest Service



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