Birds of prey plant, also known as Crotalaria spectabilis, is a species of flower belonging to the legume family Fabaceae. This plant is native to tropical regions of Asia and Africa, but it has become an invasive weed in many other parts of the world. Despite its attractive yellow flowers, birds of prey plant contains toxic pyrrolizidine alkaloids that can cause liver damage and other health effects if ingested by humans or animals. Understanding the toxicity of this plant is important to protect both people and wildlife.
What are pyrrolizidine alkaloids?
Pyrrolizidine alkaloids (PAs) are naturally occurring toxins produced by thousands of plant species worldwide, including birds of prey plant. PAs likely serve as a chemical defense to deter herbivores from eating the plants. Over 600 unique PAs have been identified and they all share a similar chemical structure. PAs are hepatotoxic, meaning they can damage the liver. The liver is the main site of PA metabolism and toxicity. When ingested, PAs are converted by the liver into reactive metabolites that can bind to liver proteins and DNA, disrupting normal cellular function. This results in liver cell damage or death.
Acute vs chronic PA toxicity
PA toxicity occurs along a spectrum from acute to chronic:
- Acute toxicity from a single high dose can cause rapid onset of liver failure and death.
- Chronic, repeated lower exposures over months or years can lead to vascular disease, liver fibrosis, cirrhosis, and cancer.
The toxicity and safe exposure thresholds for many PAs have not been fully established. But it is clear that birds of prey plant and other PA-containing plants should not be consumed in large quantities.
Toxicity of birds of prey plant
Birds of prey plant contains several toxic PAs with monocrotaline being one of the main compounds. Monocrotaline is one of the most hepatotoxic PAs identified. Ingesting small amounts of birds of prey plant can be toxic to humans and animals. Documented effects include:
- Liver necrosis and hemorrhage
- Pulmonary edema and hemorrhage
- Kidney damage
- Birth defects and miscarriage in pregnant livestock
Toxic doses leading to poisoning can occur at PA concentrations as low as 1-3% of animal body weight. Studies in rats estimate the lethal dose of monocrotaline to be around 50-100 mg per kg body weight. But toxicity thresholds are expected to be much lower for chronic exposure.
Livestock and wildlife can be poisoned after repeatedly grazing on plants like birds of prey over weeks or months. Contaminated hay or silage is another exposure risk. Humans may be poisoned by PA-containing herbal products, teas, or bushmeat from animals that ingested the plants.
Where is birds of prey plant found?
The native range of birds of prey plant covers tropical regions in Africa and Asia, including:
- Indian subcontinent
- Southeast Asia
- Northern Australia
- Middle East
- Sub-Saharan Africa
But as an invasive weed, birds of prey now grows in many other warm regions globally, such as:
- Southern United States
- South America
- Pacific Islands
- Caribbean islands
It thrives in open disturbed areas, along roadsides, forest margins, pastures, and abandoned cropland. Birds of prey spreads readily as seeds disperse through animal dung or contaminated hay. The plant also has rapid growth and can quickly colonize new areas. Identifying and removing weedy birds of prey is important to protect grazing animals and native plant communities.
Birds of prey distribution
| Region | Native or Introduced |
|---|---|
| Indian subcontinent | Native |
| Southeast Asia | Native |
| Northern Australia | Native |
| Middle East | Native |
| Sub-Saharan Africa | Native |
| Southern United States | Introduced |
| South America | Introduced |
| Pacific Islands | Introduced |
| Caribbean islands | Introduced |
Toxic effects in livestock
Livestock poisoning from birds of prey plant is well documented across its invasive and native ranges. Animals such as horses, cattle, sheep, goats, pigs, chickens and other birds can be affected after grazing on fresh plant material or contaminated hay. Some reported toxicity cases include:
- Liver disease and cirrhosis in cattle in Australia
- Hepatic veno-occlusive disease in cattle in South Africa
- Fetal malformation in pregnant cattle in Florida
- Liver lesions in horses in Brazil
- Hepatic necrosis in chickens in India
Signs of PA poisoning in an animal may include depression, weight loss, liver enlargement, yellowing eyes and gums, labored breathing, fluid buildup, and sudden death. But most chronic cases only show non-specific symptoms like poor productivity and ill thrift. Liver damage is often only detected on necropsy. There are no proven antidotes for PA poisoning so prevention is key. Producers should be vigilant in watching for the weed and keeping livestock away from it.
Livestock effects
| Livestock | Effects reported |
|---|---|
| Cattle | Liver disease, cirrhosis, fetal defects |
| Horses | Liver lesions |
| Sheep | Liver disease |
| Goats | Liver disease |
| Pigs | Liver disease |
| Chickens | Liver necrosis |
Toxicity in humans
There are a few reported cases of human poisoning from birds of prey plant. This includes toxicity from:
- Consuming contaminated grains
- Drinking herbal teas made from the plant
- Taking traditional medicines containing the plant
Documented effects in humans include liver cirrhosis, pulmonary hypertension, and cancer. However, direct causation is difficult to prove due to concomitant exposures and limited toxicological study in humans. In many parts of its native range, birds of prey plant is used in folk medicine to treat a wide variety of ailments from arthritis to uterus inflammation. The plant’s reputation as being medicinal means it is likely greatly underreported as a source of poisoning. Public education about the toxicity of medicinal plants containing PAs is important.
Human toxicity cases
| Region | Source of Exposure | Reported Effects |
|---|---|---|
| Afghanistan | Contaminated grain | Liver disease |
| South Africa | Herbal tea | Hepatocellular cancer |
| India | Ayurvedic medicine | Cirrhosis |
| Morocco | Grain and herbal tea | Pulmonary hypertension |
Risks to wildlife
In addition to livestock, native wildlife species are also at risk of poisoning from invasive birds of prey plant. Deer, small mammals, wild birds, and insects may all graze on the plant. Cases of PA toxicosis have been reported in different wildlife such as:
- Deer in California
- Cattle egrets in Florida
- Elk in Arizona
- Antelope in Idaho
Predators and scavengers can be poisoned after eating contaminated prey. Birds of prey plant also threatens rare butterfly species dependent on native host plants displaced by the invasive weed. Maintaining biodiversity and ecosystem health requires controlling birds of prey and other invasive poisonous plants.
Wildlife impacts
| Species | Region |
|---|---|
| Deer | California |
| Cattle egrets | Florida |
| Elk | Arizona |
| Antelope | Idaho |
| Butterflies | Hawaii |
Control and management
Preventing birds of prey plant poisoning requires an integrated management approach including:
- Herbicide application – Systemic herbicides like glyphosate are effective when applied to foliage.
- Mechanical removal – Hand pulling and tillage can eliminate small outbreaks.
- Grazing restrictions – Keep livestock off contaminated pastures.
- Seed bank reduction – Prevent seed production and Wear down the soil seed bank.
- Revegetation – Replant treated areas with beneficial native plants.
- Monitoring and containment – Detect and treat new weed patches early.
Chemical and mechanical methods combined with revegetation help control existing infestations. But preventing introduction and spread is most critical. Hay, livestock, cars, and equipment can transport birds of prey seed to new areas. Thorough inspection and cleaning helps stop its dispersal. Public education also raises awareness on identifying and reporting suspected poisonous plant infestations.
Conclusion
The attractive but toxic invasive plant birds of prey poses health risks to humans, livestock, and wildlife. All parts of the plant contain poisonous PAs that can damage the liver from acute high doses or chronic low exposure. Livestock deaths and human poisonings linked to birds of prey have occurred worldwide, but often go unrecognized. Understanding where birds of prey occurs, how it spreads, and its toxic effects is key for preventing exposure. While challenging to control, an integrated weed management approach can help stop the further spread of birds of prey.
