Gastrointestinal parasitism in barn owls (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is common in barn owls, both in the wild and in captivity or rehabilitation centers. These worms live in the bird's stomach, intestines, or sometimes esophagus. They feed at the e...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is common in barn owls, both in the wild and in captivity or rehabilitation centers. These worms live in the bird's stomach, intestines, or sometimes esophagus. They feed at the expense of the raptor and can cause progressive weakening of the animal when present in large numbers. This disease particularly affects young barn owls and weakened birds, which are less able to resist a heavy parasitic burden.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Signs are often subtle at first, making the disease difficult to detect in a wild bird. Progressive weight loss may be seen despite sometimes preserved appetite, dull and poorly maintained plumage, and general fatigue with the owl appearing less active. Digestive disturbances may develop: abnormal droppings, regurgitation, and sometimes visible worms in the feces or pellets. In nest-bound young, growth delay and general weakness are important warning signs. In severe cases, the bird becomes withdrawn, refuses to eat, and may show abdominal tenderness.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Several families of nematodes can parasitize the digestive tract of nocturnal raptors, particularly worms from genera commonly found in birds of prey that feed on small rodents and insects. Contamination usually occurs through ingestion of parasitized prey (rodents, insects), which explains the frequency of this parasitism in a species whose diet consists almost exclusively of small mammals.
Young barn owls, weakened or stressed birds, and those living in spaces with poor hygiene are at greater risk. A high density of parasitized prey in the bird's hunting territory, weakened immunity from concurrent illness, or captive conditions with accumulated droppings increase the risk of heavy infestation.
Transmission
Transmission occurs mainly through the food chain, when consuming parasitized prey. Eggs or larvae present in the environment (soil, perches, contaminated nest boxes) can also be ingested directly during grooming.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian relies on clinical examination of the bird and especially on microscopic analysis of droppings or pellets to look for worm eggs or larvae. In some cases, further testing may be needed to evaluate the overall impact of the parasitism on the bird's health.
Treatment
Treatment involves giving antiparasitic medication suited to birds, prescribed and dosed only by a veterinarian specializing in wildlife or exotic animals. Nutritional support and sometimes rehydration may accompany treatment in weakened birds.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
In captivity or at rehabilitation centers, regular cleaning of aviaries, nest boxes, and perches limits parasite buildup in the environment. Sanitary management of prey given to the bird, when from a breeding facility, reduces contamination risk. Regular veterinary follow-up with fecal examination allows detection of infestation before it becomes severe.
Possible complications
Untreated heavy infestation can cause anemia, severe weight loss, digestive obstruction in extreme cases, and make the bird vulnerable to other diseases. In young birds, this can seriously compromise growth and survival.
When to see a veterinarian
The bird loses weight noticeably without apparent cause. Worms are observed in droppings or pellets. The bird becomes unusually drowsy or refuses to eat. A young bird in the nest shows stunted growth or marked weakness. Digestive disturbances persist (abnormal droppings, repeated regurgitation).
Prognosis
The outlook is generally good when parasitic infection is detected early and treated by a wildlife professional. Without treatment, progressive weakening can threaten the bird's survival, particularly in young or already compromised individuals.
Frequently asked questions
Can a wild barn owl heal itself alone from a worm infestation?
A light infestation may sometimes be tolerated by a healthy bird, but a heavy parasite load requires veterinary care, especially if the bird shows signs of weakness.
How do you know if an owl brought to a care center has worms?
Diagnosis is based on microscopic analysis of droppings or pellets, performed by a veterinarian or a laboratory specializing in wildlife.
Can this parasitic infection be transmitted to humans or other animals?
Gastrointestinal nematodes of nocturnal raptors are specific to birds and do not represent a known risk of transmission to humans.
Should all owls taken in at rehabilitation centers be systematically treated?
No, antiparasitic treatment must be decided by a veterinarian after examination, as unnecessary treatment can also weaken an already frail bird.
References
ESCCAP — European Scientific Counsel Companion Animal Parasites
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 28 August 2026
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