Designing your garden to include berry-producing plants as a winter food source for birds is a good idea, but there's one plant you need to fully understand before you plant it. The red berries of Nandina domestica contain cyanide and other alkaloids that produce hydrogen cyanide (HCN), which can be poisonous to all animals, according to Audubon Arkansas.
Nandina is an attractive broadleaf evergreen ornamental, so it can be difficult to resist. It's native to Japan, China and India but is easy to grow in USDA Zones 8-10 (the South or Southeast, extending down into Florida and west toward central Texas). It will tolerate a wide range of soil and light conditions and only requires medium moisture to thrive. It has earned the common names of sacred bamboo and heavenly bamboo because it produces cane-like stems and leaves that resemble bamboo. In ideal growing conditions, a mature plant can reach a height of 4-8 feet with a spread of 2-4 foot feet. In the spring, large clusters of white flowers emerge at the end of the stems that will turn into vast quantities of bright red berries in the fall. Those berries last through the winter, long after other avian food supplies have disappeared.
Berries are the reason many gardeners grow nandina. In addition to providing visual interest, berries serve as a food source for birds during the coldest time of the year when other food can become scarce. Even robins, mockingbirds, bluebirds and other species that typically feed on worms, insects or seeds during warm months will seek out berries during the winter when their preferred food sources become hard to find.
Unfortunately for cedar waxwings, which are voracious berry consumers, nandina berries can be a last-meal death sentence.
Too much of a not-so-good thing
Nandina berries actually have a low toxicity, but they can be lethal to cedar waxwings specifically because their feeding habits differ dramatically from that of other birds, said Rhiannon Crain, project leader for the Habitat Network with The Nature Conservancy and Cornell Lab of Ornithology. "Other birds don't eat as much or as rapidly as cedar waxwings," said Crain. "Cedar waxwings completely stuff every possible part of their body with berries. They will fill their stomach and their crop with berries right up into their mouth until they can't fit another berry inside of them."
Cedar waxwings, which travel in flocks, will fly into a berry-producing bush or tree and strip the branches of every piece of fruit. That can have negative consequences for them even when the plant isn't a nandina. "I've seen them drunk on mulberries," said Crain. "Mulberries, and other fruits high in sugar can turn into alcohol, or ferment, pretty readily on the plant. They will fly into a mulberry tree and eat until they are drunk."
To understand why nandina berries can kill cedar waxwings but not other birds, Crain said to think of an apple seed, which also contains cyanide. "If you eat an apple seed, you would not feel any ill effect. But, instead of eating a single apple seed, if you were to somehow eat a plate of apple seeds, that might start to be a problem for your body." In the same manner, nandina berries are not likely to be a problem for overly curious pets or children, said Crain. They are not likely to eat enough of them for the low toxicity of the berries to cause a health problem.
But the cedar waxwings' small bodies are a mismatch for their gorging habit. "It's really a matter of ingesting enough of the nandina berries that the toxicity in the berries has a measurable impact on their bodies," said Crain.
What cedar waxwings eat
Luckily for cedar waxwings, nandina berries are not their first choice on the winter avian buffet. Crain thinks that's because other berries simply taste better to the birds; it's not that birds have an innate ability to distinguish between toxic and nontoxic berries or whether a berry or fruit is from native or non-native plants. "Most of the reasons I know about show that birds feed pretty indiscriminately on both native and non-native berries, especially if they have the same nutritional profiles."
They also can't discriminate between what might be toxic to them and what is safe, she said. "Birds tend to eat the things that they like best first," she added. They will only turn to things they like less when they run out of options.
"It's like when we taste something fatty such as a hamburger. It tastes delicious in a way that leaves of spinach never would," Crain said. "I'm guessing birds discriminate that way. But, certainly, if I was hungry, I would eat as much spinach as I could!"
The problem for cedar waxwings comes in winter's last gasp, when food sources are dwindling and they start running out of options. Nandina is always there. "As berries become more scarce in February and March, and the birds are really hungry and becoming more desperate they will eat more and more kinds of fruits. There are reports of robins and other birds feeding on nandinas as well," Crain said.
But, Crain pointed out, there are no documented avian deaths directly linked to nandina consumption other than cedar waxwings. The most well-known instance of this phenomenon occurred in Thomas County, Georgia, in April 2009 when many cedar waxwings were found dead in a residential yard. The College of Veterinary Medicine at the University of Georgia confirmed that five of the birds submitted to them had died of cyanide toxicity after consuming nandina berries.
Better berry choices
The best way for homeowners to avoid unintentionally creating an attractive but potentially lethal food source for cedar waxwings is to plant native species, advised Crain. She suggests five native species with similar growth habits to nandina that she said would grow well from Washington, D.C., down through the Southern states. They are:
- American beautyberry (Callicarpa Americana). This is a shrub that is about the same size as nandina and produces interesting white or purple berries. "I know a lot of people in the Northeast who are super jealous because it is not native there," Crain said. "They would love to have those in their yard. It is a great showy plant."
- Northern spicebush (Lindera benzoin). This plant can grow into a large shrub or small tree. It produces small yellowish flowers in spring before the leaves appear. The flowers turn into bright red fruits in September. The plant gets its name from these berries, which have been used as a substitute for allspice. "This is another great plant that would grow well in the Southeast where you might be planting nandinas," said Crain.
- Chokeberry (Aronia arbutifolia). This is a species of chokeberry that produces red berries that persist into winter. Because the berries have a sour taste for the human palate they are more often used in processed jams and other foods rather than eaten off the bush. Chokeberry gets its name from the astringency of the fruit, which can cause a choking sensation. Like with nandina berries, chokeberries are sometimes reported as being one of the last to be consumed in the winter — although this is not a universal rule.
- American holly (Ilex opaca). This native evergreen has lustrous, dark green leaves and a slow to medium growth habit. It's found from Massachusetts to Texas and across the Southeast. Female trees produce an abundance of red berries but to do, they must be planted within range of a male pollinator. "This is a showy evergreen that has big berries and a slightly different growth habit than nandina," said Crain. "But homeowners can make it work in almost any space where they have a nandina."
- Wax myrtle (Morella cerifera). Not all birds will consume wax myrtle, but it has been documented in the fecal matter of many species, including myrtle warblers, gray catbirds and tree swallows. Myrtle warblers, in particular, have a special relationship with this plant — the warblers specialize on this plant, allowing them access to a food source without as much competition, and the plant benefits from seed dispersal.
One other thing to keep in mind as you create a garden with year-round interest for yourself and wildlife: cedar waxwings are not migratory birds in the sense of songbirds that migrate through flyways to the tropics. People are often confused about that, she said, because they tend to see them in their yards in flocks in the winter and then, suddenly, the birds are gone.
Their typical range in the winter, she said, is roughly south of an imaginary line through the middle of the country. They drift northward in the warm months to breed. As the weather turns cold in the fall and winter, they move south and concentrate in the Southeastern coastal plains where they remain during the winter. Once there, they follow food. "So, they will get together in flocks, be in one place, eat everything that's there and then drift over to another location looking for berries in that place."
Seeing a flock of them descend into a berry-laden bush and strip the plant of its fruit is one of the delights of the winter garden — as long as the berries aren't nandinas.