Gastrointestinal parasitism in the Eurasian eagle-owl (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a common condition in Eurasian eagle-owls (Bubo bubo), whether kept in aviaries, rehabilitation centres or falconry facilities. These worms live in the raptor's stomach, intest...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a common condition in Eurasian eagle-owls (Bubo bubo), whether kept in aviaries, rehabilitation centres or falconry facilities. These worms live in the raptor's stomach, intestine or sometimes oesophagus. They feed at the bird's expense and in large numbers can cause significant debilitation. Young birds, stressed captive birds and those living in poorly maintained enclosures are most commonly affected.
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. Progressive weight loss may be seen despite maintained appetite, or conversely reduced appetite may develop. Plumage becomes dull and poorly maintained. Some birds regurgitate more frequently than normal or pass abnormally loose or variable droppings. Mild abdominal distension is sometimes visible in young birds. With heavy infestations, the bird becomes depressed, remains hunched on the perch and young birds may show stunted growth. Occasionally worms or worm segments are visible in the droppings or in regurgitated food pellets.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by gastrointestinal nematodes, particularly species from the genera Capillaria, Porrocaecum and Contracaecum, frequently found in nocturnal raptors. These worms lay eggs that are shed in the droppings and contaminate the environment. The bird becomes infected by ingesting eggs or larvae present on the ground or in contaminated water, or by eating prey (insects, small rodents, birds) that harbour infective larvae (intermediate hosts).
Young eagle-owls, whose immune system is still immature, are most vulnerable. Captivity in aviaries with irregularly cleaned floors, high bird density, chronic stress or a diet based on uncontrolled wild-caught prey increases risk. Birds weakened by other illness or recently admitted to rehabilitation centres are also more susceptible.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based on faecal screening examination (search for worm eggs under the microscope), sometimes repeated because egg shedding can be irregular. The veterinarian also assesses the bird's general condition, weight and plumage. In some cases, endoscopy or post-mortem examination allows direct confirmation of worms in the digestive tract.
Treatment
Treatment uses antiparasitic drugs from the benzimidazole or macrocyclic lactone families, selected and tailored by the veterinarian according to the worm species identified. Nutritional support and rehydration may be provided if the bird is significantly weakened. Complete cleaning of the bird's environment always accompanies drug treatment to prevent immediate reinfestation.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Regular cleaning of aviaries and frequent removal of droppings limit contamination of the environment. It is advisable to avoid feeding the bird with uncontrolled wild prey and to prefer healthy captive-bred prey. Periodic faecal screening examinations performed by a veterinarian allow detection of infestation before symptoms appear. Quarantine of new birds before their introduction into a shared aviary is also recommended.
Possible complications
Untreated heavy infestation can lead to intestinal obstruction, chronic inflammation of the digestive tract, severe weight loss and overall decline in immunity, making the bird more vulnerable to secondary infections. In young birds, lasting growth retardation is possible.
When to see a veterinarian
The bird is losing weight despite apparently normal feeding.
Plumage becomes dull, ruffled or poorly maintained persistently.
Worms or segments are visible in droppings or regurgitated material.
The bird remains lethargic, prostrate or refuses food for several days.
A young eagle-owl shows apparent growth retardation.
Prognosis
Prognosis is generally favourable if infestation is detected and treated early. It becomes more guarded in cases of heavy infestation, delayed treatment or in a bird already weakened by other conditions.
Frequently asked questions
Can an eagle owl in an aviary catch worms without contact with other birds?
Yes, infestation primarily occurs through contaminated environment (soil, water) or through consumed prey, not solely through direct contact with another parasitized bird.
How can I tell if my owl has worms without taking it to the vet?
There is no completely reliable sign visible to the naked eye: only an examination of droppings by a veterinarian can confirm an infestation, even in the absence of visible symptoms.
Is gastrointestinal parasitism dangerous for the human who handles the bird?
Gastrointestinal nematodes of raptors are not considered transmissible to humans under normal handling conditions.
Should all owls in the same aviary be treated systematically?
The veterinarian assesses each case individually, but often collective treatment is recommended if one bird is positive, since the others share the same contaminated environment.
References
ESCCAP — European Scientific Counsel Companion Animal Parasites
WSAVA — World Small Animal Veterinary Association
Content reviewed by the TunisieVet editorial team · Updated 28 August 2026
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