Hornbills are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. There are 54 species of hornbill, characterized by their large beaks which have a casque on the upper mandible. Hornbills are omnivorous birds, meaning they eat both plant and animal matter. Their diet consists of fruit, insects, small reptiles and mammals.
Fruit
Fruit forms a major part of the diet of hornbills. They use their large beaks to pluck and peel fruit from trees and bushes. Hornbills favor figs above all other fruits, relying on fig trees as a key food source. Figs have a unique symbiotic relationship with hornbills whereby the birds eat the figs and disperse the seeds, promoting regeneration of fig trees. Besides figs, hornbills eat other fleshy fruits including berries, drupes and capsular fruits. Studies of hornbill scat and stomach contents reveal some of the many wild fruits they consume:
- Figs – Ficus spp.
- Singapore almond – Terminalia catappa
- African cherry – Prunus africana
- Jambul – Syzygium cumini
- Wild date – Phoenix sylvestris
- Kapok tree – Ceiba pentandra
- Sausage tree – Kigelia africana
- Marula – Sclerocarya birrea
- Jackalberry – Diospyros mespiliformis
- Golden apple – Spondias dulcis
- Jujube – Ziziphus jujuba
- Pod mahogany – Afzelia quanzensis
- Numerous Ficus spp. figs
When feeding on fruit, hornbills act as important seed dispersers. As they fly between fruiting trees they transport and spread the seeds to new areas in their droppings. The large size of hornbill beaks allows them to take on bigger fruits than other avian fruit-eaters.
Insects
After fruit, insects make up the next biggest proportion of the hornbill diet. Insects provide an essential source of protein and fat for hornbills. Some of the insect prey commonly eaten includes:
- Beetles – Scarabs, longhorns, weevils
- Cicadas
- Grasshoppers and crickets
- Cockroaches
- Ants
- Caterpillars and moth larvae
- Termites
- Bees, wasps and their larvae
- Dragonflies
- Praying mantises
- Spiders
- Centipedes and millipedes
Hornbills use their massive bills to capture and consume insects. They may glean stationary insects from the bark and leaves of trees. Or snatch flying insects like bees, wasps and butterflies out of the air. Certain insects like termites are dug out of mounds or rotting wood. Caterpillars are plucked from vegetation. The casque on the upper mandible functions like a scoop that guides food into the throat.
Small vertebrates
While predominantly frugivorous and insectivorous, hornbills supplement their diet with small vertebrate prey. This includes:
- Small reptiles – Lizards, geckos, chameleons
- Amphibians – Frogs, toads, newts
- Rodents – Mice, rats, squirrels, chipmunks
- Small birds
- Bats
- Fish
- Eggs and nestlings
Prey is captured with the bill then tossed back and swallowed whole. Hornbills are opportunistic and generalist feeders, taking whatever suitably sized vertebrate prey they encounter.
Feeding methods
Hornbills have a varied foraging repertoire allowing them to exploit food across forest strata from canopies to ground level:
- Perch-hunting – Sitting stationary on an exposed perch scanning for prey animals moving on the ground or in vegetation.
- Hawking – Catching insects and other prey while in flight.
- Bark stripping – Using the bill to pry and peel bark off trees to uncover hidden insects.
- Digging – Excavating soil, mounds and rotten wood to find burrowing insects like termites.
- Probing flowers – Inserting the bill into flowers to drink nectar and collect pollen.
- Gleaning – Plucking stationary prey from branches and leaves.
- Excavating – Using the powerful bill to dig out fruits and seeds from wood or fruit shells.
Most hornbills are solitary foragers. But some species, like the southern ground hornbill, cooperatively hunt and feed in family groups encompassing up to 10 birds. Their cooperative strategy allows them to subdue larger prey like hares, lizards and snakes.
Preferred habitats
Hornbills source food from a variety of habitat types including:
- Tropical and subtropical forests – Primary source of fruits, insects and small vertebrates.
- Savannas – Scattered trees provide fruits and perches for hunting.
- Wetlands – Abundant insects, amphibians and fish.
- Cultivated areas – Crops and orchards can provide additional fruits.
Forest-dwelling hornbills rely on contiguous tracts of forest to supply enough fruit and prey within their large home ranges. Fragmentation and loss of native forest limits food resources, resulting in fewer hornbills able to persist.
Diet adaptations
Hornbills have many specialized adaptations to take advantage of dietary resources:
- Large, curved bill – Allows them to pick and handle larger, harder fruits and prey items.
- Casque on upper mandible – Serves as a scoop to direct food into the throat.
- Long tongues – Lets them probe deep into flowers for nectar.
- Strong jaw muscles – Generates biting force to crack open hard fruits and seeds.
- Wide gape – Allows them to swallow larger items whole.
- Binocular vision – Enhances depth perception and aim when hawking insects.
- Color vision – Assists spotting fruits among foliage.
- Symbiotic gut flora – Aids digesting plant matter, especially cellulose.
Breeding season diet
During breeding season, hornbills seek out energy-rich foods to meet the demands of reproduction. Key food sources at this time include:
- High fat insects – Caterpillars, beetle larvae.
- Energy-rich fruits – Figs, lipid-rich drupes.
- Nectar and pollen from flowers.
- More vertebrate prey to gain protein.
Female hornbills depend on the male to provide food during the 3-4 months she remains sealed inside the nest cavity with the eggs and then young chicks. The male makes up to 20 foraging trips a day to find sufficiently rich foods to sustain the female and their offspring.
Chick diet
Once the female emerges from the nest, both parents supply food for the growing chicks. The hornbill chick diet consists of:
- Regurgitated fruit pulp.
- Insects – Caterpillars, cicadas, grasshoppers, crickets.
- Small vertebrates – Lizards, frogs, rodents.
- Nectar and flower parts.
The chicks beg loudly for food and are fed several times an hour, increasing to over 20 times a day as they get older. This continues for 50-70 days until the chicks fledge and leave the nest.
Foraging ranges
Different hornbill species have varied foraging ranges:
- Southern ground hornbill – Up to 250 square km.
- Rhinoceros hornbill – 15-30 square km.
- Helmeted hornbill – Up to 100 square km.
- Great hornbill – 2-20 square km.
- Wreathed hornbill – 0.5-10 square km.
Larger ranges belong to bigger-bodied hornbills with higher energy requirements. Smaller species can meet their dietary needs in smaller, more concentrated areas. Males expand their foraging areas during breeding season to supply sealed females.
Daily dietary intake
Food intake varies by hornbill species and factors like time of year. On average during non-breeding seasons, daily intake consists of:
- 50-90% fruit – Figs prominent during fruiting season.
- 5-40% insects and other invertebrates.
- 5-15% small vertebrates – More during breeding season.
- 5-10% nectar and flowers.
Large hornbills like the great hornbill eat around 250-350 grams of food per day on average. Smaller species consume proportionally less at roughly 50-150 grams daily.
Role as seed dispersers
Through their frugivory, hornbills provide vital seed dispersal services for forest plants. Their key ecological roles include:
- Ingesting fruits whole and regurgitating seeds.
- Carrying seeds away from the parent tree, avoiding competition.
- Dropping seeds in nutrient-rich droppings fertilizes growth.
- Distributing seeds over wide areas via their large ranges.
- Dispersing seeds too large for other frugivores.
Loss of hornbills can disrupt forest regeneration and plant dispersal dynamics. Large figs become over-abundant near parent trees without hornbills to spread them.
Diet composition by species
The proportion of different food types in the diet varies across hornbill species based on morphology and habitat. Some examples:
Southern Ground Hornbill
- 30% insects, other invertebrates
- 15% reptiles and amphibians
- 20% small mammals
- 15% birds, eggs, chicks
- 10% fruits
- 10% seeds, grains
Rhinoceros Hornbill
- 70% figs, fruits
- 15% insects, other invertebrates
- 10% small vertebrates
- 5% nectar, flowers
Great Hornbill
- 55% fruits
- 30% insects, other invertebrates
- 10% small vertebrates
- 5% nectar, flowers
Wreathed Hornbill
- 80% figs, fruits
- 10% insects, other invertebrates
- 5% small vertebrates
- 5% nectar, flowers
Threats from declining food resources
Habitat loss poses major threats to hornbill food supplies including:
- Forest clearing for agriculture and logging.
- Livestock overgrazing reducing insects, vegetation.
- Hunting pressure on prey species.
- Fragmented forests with fewer fruiting trees.
- Invasive plants crowding out native fruiting trees.
- Climate change altering plant fruiting seasons.
As forests disappear and food becomes scarce, hornbill numbers decline. Preventing further habitat loss is crucial for preserving hornbill food resources.
Conservation importance
Forty percent of hornbill species are currently threatened with extinction according to the IUCN Red List due to factors like food resource decline. Conserving remaining intact forests where hornbills forage is essential for protecting these unique birds and their ecological roles in seed dispersal and control of prey populations.
Conclusion
Hornbills are remarkable birds uniquely adapted to take advantage of a wide array of food resources. Their expansive diet of fruit, insects and small vertebrates is supported by specialized features like large casqued bills. As important seed dispersers and regulators of forest food webs, maintaining the intricate diet of hornbills is crucial for preserving healthy ecosystems that sustain all life.