It is a common sight to see birds feasting on colorful berries that adorn garden plants and wild shrubs. This observation often leads to a puzzling question: why can birds eat berries that are known to be poisonous to people and their pets? The answer lies not in the berries themselves, but in the distinct physiological traits that separate avian and mammalian life.
Avian vs. Mammalian Physiology
The ability of birds to consume toxic fruits is largely due to their adapted digestive systems and metabolic processes. A primary factor is the speed of their digestion. For many fruit-eating birds, like a thrush, berries can pass through their entire digestive tract in as little as 30 minutes. This rapid transit time is a survival advantage, minimizing the period for toxins to be absorbed into the bloodstream.
Beyond speed, the internal chemistry of birds plays a role. Avian livers and gut microbiomes can neutralize chemical compounds that are harmful to mammals. For example, some birds possess gut bacteria capable of breaking down toxic alkaloids found in certain nectars and fruits. This process renders poisons harmless before affecting the bird’s system. This metabolic capability is a product of evolution, allowing birds to exploit food sources unavailable to competitors.
Birds may also lack the biological receptors that respond to certain irritants. A well-known example is capsaicin, the compound that makes chili peppers hot. Mammals have pain receptors that react intensely to capsaicin, but birds do not, allowing them to eat the hottest peppers without discomfort. This insensitivity extends to other plant compounds, so some berry toxins do not trigger a harmful reaction in birds.
Common Garden Berries Toxic to People and Pets
Many ornamental plants produce berries that are food for birds but pose a risk to humans and pets. Identifying these plants can prevent accidental poisoning. Their bright berries add color to landscapes, which can make them attractive to children and pets.
- Holly: These shrubs have glossy, pointed leaves and bright red berries. While a meal for species like the American Robin, the berries contain saponin, which can cause nausea, vomiting, and diarrhea in people.
- Yew: A common evergreen hedge, this shrub produces a soft, red, cup-like berry. Birds eat the fleshy part, but the seed, leaves, and bark contain taxine alkaloids that can cause dizziness, breathing difficulty, and severe heart rate changes in humans.
- Pokeweed: This tall plant has purple-red stems and dark purple berries in grape-like clusters. The entire plant is toxic to humans and pets, with toxicity increasing as it matures. Eating as few as 10 berries can result in headaches, severe stomach pain, vomiting, and diarrhea.
- American Mistletoe: A parasitic plant found in trees, it produces waxy, white berries containing phoratoxin. Ingestion by humans or pets can cause stomach upset, a slowed heartbeat, and in severe cases, convulsions.
Safety and Precautionary Measures
The most important rule regarding wild berries is to never consume them unless you are certain of their identity and safety. The popular advice to eat what birds eat is dangerously misleading and should never be followed. Many plants have evolved to use birds for seed dispersal while developing toxins to deter mammals.
If an adult, child, or pet ingests a berry from an unknown plant, take immediate action. Contact the Poison Control Center at 1-800-222-1222 or a veterinarian immediately. Do not wait for symptoms to appear, as some toxins can have a delayed effect.
When calling for help, provide as much information as possible. This includes the person’s or pet’s age and weight, a description of the berry and plant, how many berries were eaten, and any symptoms that are present. If it can be done safely, a picture of the plant or a sample of the leaf and berry can help experts make a positive identification.