Bucorvus leadbeateri (Vigors, 1825)
サバンナに響く低音のデュエット
Booming Duets of the Savanna
サイチョウ類の中でも最大級の種で、体長は約1〜1.1m、体重は4〜6kgに達します。全身は光沢のある黒い羽毛に覆われ、太く大きく湾曲した嘴と、目の周囲から喉にかけて広がる鮮やかな赤い裸出皮膚が特徴です。雌雄は外見で見分けることができ、顎の下に垂れるワトル（喉の裸出部）が完全に赤いのが雄で、雌では青紫色の斑紋が入ります。アフリカ南部から東部にかけて分布し、サバンナや疎林、開けた森林地帯に生息します。昼行性で、群れを作って地上を歩き回りながら昆虫や爬虫類、小型哺乳類、鳥類の雛、果実、種子など多様な餌を探します。群れは通常2〜9羽で構成されますが、その中で繁殖できるのは優位な一組のペアのみです。繁殖期には樹洞などに巣を作り、通常2個の卵を産みますが、多くの場合は一羽だけが成長します。子育てはペアだけでなく群れの他の個体も参加し、餌を運ぶなど協力して雛を育てる「協同繁殖」の習性を示します。寿命は非常に長く、野生では40〜50年、飼育下では70年近く生きる例も知られています。鳴き声は遠くまで響く低い声「booming」と呼ばれる発声で、喉の裸出部を膨らませて発する重低音は数km先まで届くとされ、縄張りの主張や群れ同士の連絡に用いられます。また、この発声を基調として雄と雌が交互に声を合わせるデュエット鳴きを行うこともあり、つがいの結びつきや群れ内のコミュニケーションに重要な役割を果たしていると考えられています。
The Southern Ground Hornbill is one of the largest hornbill species, reaching about 1.0–1.1 m in body length and weighing up to 4–6 kg. Its body is covered in glossy black plumage and it is distinguished by a large, strongly curved bill and vivid red bare skin extending from around the eyes to the throat. Males and females can be distinguished by the wattle beneath the lower bill: in males it is entirely red, whereas females show bluish-purple patches. The species occurs in southern and eastern Africa, inhabiting savannas, open woodlands, and lightly forested landscapes. It is diurnal and typically forages on the ground, walking in groups while searching for a wide variety of prey and food items such as insects, reptiles, small mammals, nestling birds, fruits, and seeds. Groups usually consist of two to nine individuals, but only the dominant pair within the group breeds. During the breeding season the pair nests in a tree cavity and typically lays two eggs, although usually only one chick survives to maturity. Parental care is not limited to the breeding pair: other members of the group help feed and guard the chick, a system known as cooperative breeding. The species is also remarkably long-lived, with individuals living 40–50 years in the wild and up to around 70 years in captivity. Its vocalization is characterized by a deep, resonant call known as “booming.” Produced by inflating the bare throat skin, this low-frequency sound can carry for several kilometers and is used for territorial advertisement and communication between groups. Based on this call, males and females sometimes perform alternating duet calls, which are thought to strengthen pair bonds and facilitate communication within the group.
参考文献
“Southern ground hornbill” National Geographic. 2026年4月12日閲覧
“Southern Ground-Hornbill” World Land Trust. 2026年4月12日閲覧
“Bucorvus leadbeateri” Animal Diversity, University of Michigan. 2026年4月12日閲覧