Southern Ground Hornbill (Bucorvus leadbeateri) Fact Sheet: Reproduction & Development

Mating behavior

• Only dominant group male and female copulate (Kemp 1988; Kemp and Kemp 1980)
• Form long-term bonded pairs (Kemp 1988)
• Male initiates copulation
• Forcefully preens the female’s head and neck, pushing her down (Kemp 1988; Kemp and Kemp 1980)
• Female assumes a crouched position as the male steps on her back
• Male grasps her nape with his bill
• Other group males may harass the copulating pair

Copulation (from Kemp and Kemp 1980 unless otherwise noted)

• Location
• Occurs on a tree branch (Kemp 1988; Kemp and Kemp 1980)

Seasonal reproduction (from Kemp 1988 unless otherwise noted)

• Breed in late summer, in South Africa (from Kemp and Kemp 1975; Kemp and Kemp 1991)
• During the wet season
• Egg laying
• Begins in mid-October (spring), South Africa (Kemp and Kemp 1980)
• Early reproductive efforts are more successful than those later in the season (Kemp and Kemp 1991)
• Similar pattern of seasonal reproduction in Zimbabwe (Msimanga 2004)

Co-operative reproduction, unlike Northern Ground Hornbill (Kemp 1995)

• One monogamous breeding pair per territory (Kemp 1988; Kemp 1995)
• Dominant male and female breed (Kemp 1988)
• All other adults and juveniles provide the nesting female with food (Kemp 1988)
• System may provide reproductive benefits in an area with limited breeding vacancies (Kemp 1988)
• Group members provide food to the female and chick (Kemp and Kemp 1980)
• Group collectively visits the nest 3-4 times per day with provisions (Kemp 1995; Kemp and Kemp 1980)

Reproductive rate

• Low reproductive rate (Kemp and Kemp 1975)
• 6 chicks born to 55 birds during the course of one 2 year study (Kemp and Kemp 1975)
• Mean rate of successful breeding
• c. once every 6.3 years a group will successfully reproduce (Kemp and Kemp 1980)

Nest in cavities (from Kemp and Kemp 1980 unless otherwise noted)

• Commonly use the same nest year after year (Kemp and Kemp 1975; Kemp and Kemp 1980)
• Often use natural cavities formed by rot damage on tree branches or trunks (Kemp and Begg 1996)
• Nests used for at least 10 years, in the Natal region of South Africa and Zimbabwe (Knight 1990; Msimanga 2004)
• Nest location and selection
• Located in large stumps, trees, or in rock holes (Kemp and Kemp 1975; Witteveen et al. 2013)
• In trees, commonly 4-10 m (13-33 ft) above the ground (Kemp and Kemp 1980; Witteveen et al. 2013)
• Trees serve as the most common nest sites in Kruger National Park, South Africa and Zimbabwe (Kemp and Begg 1996; Msimanga 2004)
• Granite crevice nests typically located 11-15 m (36-49ft) above ground, Matobo National Park, Zimbabwe (Witteveen et al. 2013)
• Most common nest location in Matobo National Park (Witteveen et al. 2013)
• Kruger National Park birds uncommonly nest in rock holes (Kemp and Begg 1996)
• Site selection
• Dominant female leads group members to visit possible nest holes
• Typically during the course of foraging
• Often in early morning, before 09:00
• The dominant female visits the selected nest site almost daily
• She spends several hours in the nest each day
• Sits in and arranges nest for up to 5 hours
• Pecks loose wood off interior and positions lining
• Adult males bring her food and nesting material (dry grasses and leaves)
• Food items are tucked into nest lining; the female sorts through the deposited load to pick out and eat her meal

Clutch characteristics (from Kemp 1988 unless otherwise noted)

• Egg features
• Shell white and pitted (Courtnay-Latimer 1942; Kemp 1988)
• Ovoid in shape, elongate and pointed at one end (Kemp 1988; Sclater 1902)
• Size measures
• Weight
• 60-100 g (2.1-3.5 oz)
• Dimensions vary by region
• c. 70 x 50 mm (2.8 x 2.0 in), eggs sampled from a Transvaal population
• c. 74 x 52 mm (2.9 x 2.0 in), eggs sampled from a Zimbabwe population
• 1st laid egg larger than 2nd
• Clutch size
• 1-3 eggs per clutch (Kemp 1988; Kemp et al. 2007; Msimanga 2004)
• 2 eggs most commonly; rarely 3 (Kemp 1988; Kemp et al. 2007)
• 3-5 day interval separates laying of each egg
• Second chick does not survive, in most cases (Kemp and Kemp 1980)
• Unable to compete with older sibling
• Likely produced as insurance against hatch failure of the 1st egg

Incubation (from Kemp 1988 unless otherwise noted)

• Participants and behaviors
• Dominant female incubates eggs
• Begins immediately after 1st egg is laid
• Spends much of her time in the nest; including nights when other groups members roost nearby (Kemp and Kemp 1980)
• Egg not incubated continuously (Courtenay-Latimar 1942)
• Female joins group members near the nest on most mornings (Kemp and Kemp 1980)
• Nest left unattended for up to c. 30 minutes several times throughout the day (Kemp and Kemp 1980)
• Duration
• c. 40 days

Hatch (from Kemp 1988 unless otherwise noted)

• Hatchlings
• Appearance at hatch
• Blind
• Naked; skin pink
• Bill grey with a white tip (Kemp and Kemp 1980)
• Upper mandible shorter than lower
• Size at hatch
• Mass c. 82 g (3 oz), one individual (Kemp and Kemp 1980)
• Hatch interval
• Clutch mates hatch 3-5 days apart
• Eldest chick weighs significantly more than younger by the time of its hatch
• May weigh as much as 250 g (8.8 oz) before its younger sibling hatches
• Younger chick most often does not survive; dies of starvation

Reproductive interval

• May not breed annually (from Kemp 1995)
• Often breed after a good start to the summer rains

Infants

• Care
  • Fed by mother until old enough to consume larger items
    • All group members provide food for mother and chick (Kemp and Kemp 1975)
• Development (from Kemp 1988 unless otherwise noted)
  • Within 3 days of hatch, skin turns dark purple
  • c. 7 days
    • Eyes begin to open
    • First feather quills emerge
    • Dorsal airsac fully develops
  • c. 14 days
    • Eyes are fully developed
    • Body is covered in short spiny quills
    • Throat is bare and partially inflated
  • c. 21 days
    • Quills nearly breaking open into feathers
    • Legs are strong and well developed
  • c. 30 days
    • Feathers cover most of the body
    • Wing and tail feathers continue to grow
  • 3 months
    • Chicks begin to fledge the nest (Kemp and Kemp 1975)

Immatures and subadults (from Kemp 1995)

• Remain with birth group until mature, 4-6 years of age
• Feeding
  • Can obtain own food after 6 months of age
  • Beg for food and are fed by adults until c. 2 years of age

Adults (>4 yrs)

• Sex ratio
  • Bias within family groups
    • Males typically outnumber females within a group
    • Most solitary individuals are female (Kemp and Begg 2001; Kemp 1980)
      • Population sex ratio likely closer to 1:1
• Reproductively active for many years
  • One male, an individual in managed care, reproduced well into his 40s (Sweeney and Lynch 2011)
• Males
  • Rarely seen alone (Kemp 1980)
    • Likely disperse less commonly than females (Kemp and Boesman 2013)
  • First reproduce
    • c. 4-6 years, a projected estimate based on reproductive ages of females in the wild (Sweeney and Lynch 2011)
• Females
  • Leave parental group when sexually mature to found a new family (Brooke 1984)
  • First reproduce
    • c. 4-6 years of age (Kemp 1995; Sweeney and Lynch 2011)

Wild populations

• Not well known (Spear et al. 2005) but thought to have a long life span (Kemp et al. 1989)
  • Preliminary data with small sample sizes suggest about 28 years (Kemp and Kemp 1980)
• For all hornbills, likely about 35-40 years (average life expectancy) (Kemp 1995)

Managed care

• No AZA estimates

Survival rates

• Not accurately measured (from Spear et al. 2005)
• Adults estimated to have high rates of survival, >90%
• Significant mortality threat between fledging and adulthood
• 25-31% estimated survival rate

Few observed predators (from Kemp 1995; Kemp 1988)

• Leopard, Martial Eagle, genet, and snakes

Juveniles and subadults remain with their parents for several years. Though individuals are capable of feeding themselves by 6 months of age, a 2 year old may still beg for food from its parents and older siblings.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Brooke (1984)
Courtenay-Latimer (1942)
Kemp (1988)
Kemp (1995)
Kemp and Begg (1996)
Kemp and Begg (2001)
Kemp and Boesman (2013)
Kemp and Kemp (1975)
Kemp and Kemp (1980)
Kemp and Kemp (1991)
Kemp et al. (2007)
Knight (1990)
Msimanga (2004)
Sclater (1902)
Spear et al. (2005)
Sweeney (2012)
Sweeney and Lynch (2011)
Witteveen et al. (2013)
ZIMS (2015)