Hornbills are a family of bird found in tropical and subtropical regions of Africa, Asia and Melanesia. There are over 60 species of hornbill that vary greatly in size and appearance, but they all share some common features that make them easily recognizable.
Key Identifying Features of Hornbills
All hornbills have large bills that protrude forward from their face. The bill has a casque on top, which is a hollow structure made of keratin. The size and shape of the casque varies between species. For example, the casques of Asian hornbills tend to be tall and arched, while African hornbills have shorter, more flattened casques. The purpose of the casque is not fully understood, but it may assist in echoing calls and amplifying vocalizations.
The mandibles of the bill do not join together neatly at the front. There is a gap between them even when the bill is closed, which gives them a unique profile unlike other bird groups. The bill length also varies significantly, with larger species having bills measuring up to 61 cm long.
Another distinctive feature of hornbills are their eyelashes. They have prominent black lashes on their lower eyelids. This is thought to protect their eyes when they are feeding on thorny or spiny fruits and insects.
In terms of plumage, they generally have dark wings and tails, with paler underparts and bellies. The head is often lighter as well. The plumage is unique to each species, with some having bright yellow, red or blue facial skin, throat feathers or bills.
Body Size and Shape
Hornbills come in a huge range of sizes, from the diminutive Abyssinian ground hornbill at 70 cm long, to the southern ground hornbill which can measure up to 130 cm. Their wingspans also vary dramatically, from around 50 cm to well over 150 cm across.
In terms of body shape, hornbills are short-necked and stout. They have rounded wings and fairly broad, elongated tails. Their legs and feet are strong to allow them to perch high up in trees. The toes are arranged in a zygodactyl pattern, with two pointing forward and two pointing backward.
Habitat and Distribution
Hornbills occupy a diverse range of habitats across their distribution, including forests, savanna, swamps and agricultural areas. They require tall trees for nesting, roosting and foraging, but are otherwise quite flexible in the habitats they utilize.
They are found throughout sub-Saharan Africa, with around half of all hornbill species native to that continent. The greatest diversity occurs in west and central Africa. In Asia, hornbills range from India and Sri Lanka through southeast Asia and Indonesia. Just two species, the Papuan hornbill and the Rufous-necked hornbill, are found in New Guinea and the Bismarck Archipelago.
Flight and Diet
In flight, hornbills have slow but powerful wing beats on broad wings. They may fly in straight lines or with undulations. Most hornbills are noisy in flight, with the flapping of their wings and air rushing over their wing feathers producing a variety of whirring sounds.
Hornbills feed on a wide range of items depending on habitat and species. Fruit comprises a major part of the diet of most hornbills. They also eat insects and other small animals such as lizards, frogs and rodents. Some of the larger species may even prey on smaller birds, snakes and scorpions.
Their large bills allow them to consume fruits and prey whole. The bill assists them in breaking the exoskeletons of insects and crushing the bones of small vertebrates. For fruits with hard outer shells or rinds, the hornbill may fly up into the air and then drop the fruit onto a hard surface to break it open.
Breeding Behavior
One of the most fascinating aspects of hornbill biology is their unique nesting behavior. During breeding, the female hornbill seals herself into the nest cavity, plastering up the entrance with mud, fruit pulp and droppings. Only a small slit is left through which the male passes food.
Inside, she lays eggs, incubates them and cares for the chicks without any external help. This lasts around 3-4 months until the chicks are old enough to break out of the nest. The plastered entrance likely protects the female and chicks from predators.
Taxonomy and Classification
Hornbills belong to the avian family Bucerotidae. Traditionally they were classified into one single family, but recent genetic evidence indicates they may be divided into two distinct clades:
- Bucerotinae – The African Pied Hornbill and ground hornbills
- Tockinae – All other Asian and African hornbills
There are two subfamilies currently recognized:
- Bucorvinae – Contains 9 extant species in 2 genera of ground hornbills
- Bucerotinae – Contains all other hornbills, with around 55 species
Some taxonomists separate the hornbills into up to six subfamilies to better represent their evolutionary relationships. However there is still debate over the most accurate taxonomic classification.
Here is a breakdown of the number of recognized hornbill species by region:
| Region | Number of Species |
|---|---|
| Africa | 40 |
| Asia | 32 |
| Wallacea | 2 |
Conservation Status
Around 13 species of hornbill are currently considered threatened with extinction by the IUCN. Habitat loss is the major threat facing most hornbill species worldwide. In Asia, many are endangered due to loss of primary forest habitat. Hunting for food and their casques also threatens some species.
Some examples of threatened hornbill species include:
- Writhed Hornbill – Endangered
- White-crested Hornbill – Vulnerable
- Sunda Hornbill – Vulnerable
- White-backed Hornbill – Near Threatened
- Bushy-crested Hornbill – Near Threatened
Conservation efforts are aimed at protecting remaining habitat, limiting hunting and trade, and reducing human disturbance at nest sites. Public education programs are also important to raise awareness of hornbill conservation issues.
Unique Species
With over 60 diverse species across three tropical regions, hornbills are incredibly varied in size, color and ecology. Here are some examples of unique and fascinating hornbill species:
Rhinoceros Hornbill
This spectacular Southeast Asian hornbill has a bright yellow/red bill with a large upright casque on top that resembles the horn of a rhino.
Helmeted Hornbill
The Helmeted Hornbill of Borneo, Sumatra and Malay Peninsula has an immense solid casque said to resemble ornate samurai helmets.
Southern Ground Hornbill
This African species has black plumage with bright red patches of bare skin on its face and throat pouches. It is the largest hornbill species.
Trumpeter Hornbill
With its loud, trumpeting call, this west African hornbill has a wingspan over 1.5 meters wide.
Tockus Hornbills
Referred to as “tick birds”, this African genus has relatively small casques and muted black, white and grey plumage.
Conclusion
With their oversized colorful bills, brash calls and unique nesting habits, hornbills are one of the most distinctive avian families on Earth. There is incredible diversity in size, shape, color and behavior across the 60+ hornbill species found in tropical regions worldwide. While habitat loss threatens many hornbills, increased conservation awareness and habitat protections offer hope for the future of these amazing birds.
