There are a number of birds that are known to eat bones as part of their diet. Birds that eat bones regularly are able to do so because of specialized adaptations in their digestive systems. The consumption of bones provides these avian bone eaters with important nutrients like calcium and phosphorus.
While most birds have gizzards that help grind up food, birds that frequently eat bones tend to have particularly muscular gizzards with thick walls that can exert great crushing force. These allow the birds to break down and digest hard materials like bones. Some bone-eating birds also produce stronger stomach acids than other avian species.
The act of eating bones helps supplement minerals but can also sometimes provide sustenance when other food sources are scarce. Here are some of the most common types of birds known for their ability to eat bones and how they are adapted for this somewhat unusual diet.
Vultures
Vultures are perhaps the most well known of the bone-eating birds. Species like the turkey vulture, the black vulture, and the greater yellow-headed vulture regularly consume carrion and bones as part of their scavenging habits. When eating the carcass of a dead animal, vultures are able to use their sharp, hooked beaks to cut through skin and tendons to access bones.
The turkey vulture has one of the most acidic stomach pH levels of any bird, allowing it to digest some of the more unsavory parts of a carcass including bones. While they prefer fresh carrion, turkey vultures have very strong immune systems that also let them safely eat carrion that may contain botulism or anthrax bacteria that would sicken or kill other animals.
Owls
Owls regurgitate pellets containing indigestible material from their prey like bones, fur, and exoskeletons. Since owls swallow small prey whole, bones from mice, voles, rabbits, and other small animals are common in their pellets. Dissecting these pellets lets ornithologists study the diet and health of owls.
While owls have strong stomach acid, they lack a muscular gizzard for grinding like vultures. Therefore, owls can digest but not break down large or hard bones, necessitating their regurgitation. The powerful talons and sharp beaks of owls make it easy for them to consume even rodents and birds with sizable bones.
Eagles
This family of large raptors subsists mainly on fish and small mammals. When feeding on these prey animals, eagles have no trouble consuming bones using their large, hooked beaks and razor-sharp talons.
Bald eagles have been observed dropping heavy bones from heights of 100 feet or more onto hard objects below in order to break the bones into smaller, more digestible fragments that can be swallowed.
The bald eagle’s muscular gizzard contracts with enough force to easily crunch most bones. Even if a bone shard should perforate an eagle’s digestive tract, their stomach acid is strong enough to prevent serious infection.
Seagulls
These ubiquitous ocean birds have extremely high-acid stomachs like vultures, allowing them to regularly eat bones when scavenging carcasses along the seashore. Herring gulls and related species often swallow bones whole then regurgitate pellets, though their gizzards can grind down most fish bones.
A seagull’s digestive acids are potent enough to dissolve thin bones into a soupy liquid within hours. Thick leg bones of larger animals take longer to digest but are ultimately corroded by stomach acid as well.
Storks
Several species in the stork family are also capable of eating bones. The large marabou stork of Africa is known for scavenging carcasses down to the skeleton. Their immensely powerful jaws allow them to crunch thick bones from larger animals to ingest bone marrow.
The jabiru of South America similarly feeds on carrion and uses its heavy 8-inch bill to crush bones. In addition to bone fragments, these storks also ingest the hair, tendons, and cartilage of carcasses. Parents regurgitate some of this material to feed nestlings.
Hyenas
Though not birds, hyenas are another animal group adapted for bone consumption. Spotted hyenas and striped hyenas have incredibly strong jaws and teeth that pulverize bones for ingestion. Their highly acidic stomach environment helps break down bone fragments.
Hyena droppings turn white rather than black due to the large quantity of bone powder passing through their digestive tracts. Hyenas play an important ecological role by completely consuming carcasses without waste.
Why Birds Eat Bones
There are a few key reasons certain avian scavengers and predators have adapted the ability to eat bones:
Nutritional content
The primary motivation for bone consumption in birds is nutrition. Bones are rich in minerals like calcium and phosphorus that are essential for avian health. Eating bones helps balance the diet of raptors and vultures that subsist mainly on meat which lacks minerals. marrow also provide energy.
Food scarcity
In lean times with few fresh carcasses, vultures and other scavengers broaden their diets to include bones for sustenance. Bones remain long after flesh and organs have decayed away, so they become the only available food source in such situations.
Feeding young
Regurgitating partially digested bones provides baby vultures and storks with high mineral food at a critical time for their development. Bone fragments are also easier for chicks to swallow than whole bones would be.
Hygiene
By picking carcasses clean down to bone, vultures and hyenas help prevent the spread of diseases by eliminating rotting meat and pathogens. This is an important natural sanitation function.
How Birds Physically Eat Bones
To safely and efficiently eat bones, birds possess specialized digestive tract adaptations:
Sharp beaks
Raptors like eagles and owls use hooked upper beaks and sharp lower mandibles to cut meat and access bones inside a carcass. Scavengers have strong, wide beaks to tear open skin and break apart joints.
Strong jaws
Hyenas and marabou storks have extremely powerful bite strength to crush thick leg bones and skulls. Jaw muscles and skull structure give them incredible mechanical advantage.
Potent stomach acid
Vultures and seagulls produce stomach acid that is 10 times more acidic than human gastric acid. It can dissolve bone into a semi-liquid paste within 24 hours.
Muscular gizzards
The gizzards of eagles and vultures have thick muscular walls that clench down on swallowed bones, breaking them into small fragments. Gizzards aid mechanical digestion.
Dangers of Bone Consumption
Despite their adaptations, eating bones can pose dangers for birds:
Obstructions
Too large a fragment can become obstructed in the throat, crop, or intestines, leading to injury or death. This occurs if the bird cannot adequately break the bone.
Stomach punctures
Sharp splinters of bone may puncture stomach or intestinal lining during digestion. Can lead to septicemia. More of a risk in captive birds on abnormal diets.
Nutritional imbalance
Excessive bone intake may lead to skeletal deformities over time due to interference with proper calcium and phosphorus absorption.
Toxic accumulation
Bones can accumulate heavy metals like lead. Predatory and aquatic birds are at particular risk since toxins magnify up the food chain. Can cause poisoning.
Examples of Bone-Eating Birds
Turkey Vulture
- Scavenger
- Acidic stomach liquefies rotting meat and bone
- Thrive on carrion others avoid
- Play vital role in ecosystem hygiene
Snowy Owl
- Powerful predator
- Swallows small prey whole
- Regurgitate pellets with bones
- No muscular gizzard
African Fish Eagle
- Fish are main prey
- Crunches fish bones in gizzard
- Drops large bones to break them
- Also eats carrion
Marabou Stork
- Massive African scavenger
- Scavenges carcasses to skeleton
- Crushes thick leg bones in jaws
- Regurgitates bone fragments for young
Conclusion
The ability to safely consume and digest bones provides distinct evolutionary advantages for certain avian scavenger and predator species. Vultures, eagles, owls, storks, and seabirds all possess adaptations like corrosive stomach acid, pneumatic bones, and powerful gizzards that allow them to eat bones as a food source and gain vital nutrients. However, bone eating does carry risks like obstructions and accumulations of toxins. Understanding how specialized birds eat bones provides insight into their unusual ecological niches.