White-fronted Bee-eater (Merops bullockoides) Fact Sheet: Reproduction & Development

(Wrege & Emlen 1994)

Choose one of the two rainy seasons each year for breeding

Females consider the family structure of a potential mate when choosing a partner.

• In a 5-year study of mate choice in Kenya, females preferred males with a large, genetically close family of helper- birds that could aid the pair in rearing their young.
• The advantage to the female's breeding success of a male with a "good family" is so great that a female may skip a breeding cycle rather than choose a mate of poor social quality.

Courtship interactions occur at the roosting colony and on the feeding territory.

Courtship is lengthy - often 6 to 8 weeks

At the start of courtship both birds are excluded by their families; as they form a pair-bond, the female usually becomes accepted into the male's family group.

After mating, males spend most of day guarding female from other males.

Social/reproductive system

Monogamous, cooperative breeders, living in colonies. (Emlen 1990)

Breeding success in this species strongly influenced by family structure. (Wrege & Emlen 1994)

Females typically leave their birth group to join the family of the male (patrilocal)

• Loose ties are maintained with birth group; may leave mate, if not nesting, to return home and help with nesting of a genetic parent; return to mate when task is completed. (Emlen & Wrege 1988)
• "In-laws" usually are nesting and roosting nearby. (Emlen 1990)

Many individuals of both sexes play a role as a helper at the nest. (Emlen 1990, 1991))

• They differ from other colonial birds who typically play the helper role only when young, before achieving breeding status.
• Helper birds help their close genetic relatives.
• May switch several times between breeder and helper roles.
• Some 60% of breeding pairs have 1-5 helpers. (Fry 2001)
• Nests with helping birds have much more twice as much reproductive success.
• Helper birds associate with a single nest and assist in all phases of the nesting activity.
  • Excavate tunnel
  • Defend nest
  • Bringing food to the breeding female
  • Incubating eggs
  • Feeding nestlings
  • Caring for fledglings after they leave nest

Nesting (Emlen 1990) (Fry 1984, 1992)

• Nests only dug into perpendicular cliffs.
• Usually 10-20 active nests but up to 150 nests with 450 birds.
• Highly variable level of nesting success; often not successful.
  • Many nests abandoned early (but males or females may go on to be a helper at another nest).
  • Chicks in many nests starve; with helper birds assisting the parents, less starvation.
• Helper birds assist in excavating and defending the nesting chamber, incubating the eggs, feeding and caring for young.
  • Helpers are dedicated to one nest for the nesting season.
  • If nesting effort fails, helpers plus the parents may redirect their efforts to helping another related bird pair's nesting effort.
• Benefit of helpers' work is great: each helper accounts for an average of 0.44 additional offspring; the more helpers, the better the results.
• Nest sites not necessarily chosen next to other clan members (clan members share foraging territory, not nesting area).
• One bee-eater studied (M. orientalis) could judge the line of sight of a predator and not enter the nest burrow when the predator could see the nest. (Watve et al 2002)

Egg Laying

• Incubation period: 20-21 days
• Female spends most of day (94% of time) in nest to prevent other females from parasitizing nest (she removes all foreign eggs before laying own eggs).
• About 7% of all eggs in colony are laid in another female's nest, by either another bee-eater or other bird species.

Eggs (Fry 1984)

• Clutch size: 2-5 eggs; nests with helpers have the most eggs.
• Incubation: Female parent spends more time inside nest cavity than male parent.
• Brooding: Parents allow other members of its clan to visit the nest.

Nestlings

• Chicks altricial (blind and naked when born).
• Chicks weigh an average of 4.8 g (1.7oz)
• Male parent may spend more time than females in caring for nestlings. (Fry 1984)
• Growth rates of nestlings flexible, depending on food availability. (Fry 2001) 
• In this species, nestling mortality is high - 48% of all hatchlings die of starvation. (Emlen et al 1991)
• Feather growth completed at 25 days (for well-fed chicks). (Emlen et al 1991)

Young

• Fledging at about 29 days for well-fed chicks in a study in Kenya by Emlen et al (1991)
  • Some chicks delayed fledging to as much 42 days.
  • Low food availability meant more days of delayed development.
  • Chicks born last were more likely to have delayed development, due to facing more competition for food.
  • Chick in nests with helpers (in addition to parents) had less delayed development.
• Fledglings average 22% heavier than average adults' weight.(Elston 2007)
• Both parents tended young in nest chamber equally. (Fry 1984)

Adults

• Adult plumage at 6 months.
• Young remain with parental group till about 9 months, then may pair into other social groups. (Emlen et al 1991)

Wild populations

• 5–6 years (Fry and Boesman 2020)

Managed care

• No AZA estimates

(Fry 1984) (Wrege & Emlen 1991)

Aside from flooding and cliff collapse deaths, 48% of nestlings die of starvation.

Predation on eggs and young only a minor cause of mortality

• Nest parasitizing Honeyguide birds (Family Indicatoridae) kill embryos by pecking the egg; their young kill nest mates with sharp beak-hooks.
• Predators on nests in Lake Nakuru National Park, Kenya: snakes, mongooses, swifts

Collapse of undercut cliff faces along a river are common; often considerable or total loss of colony's eggs and young.

Cliff faces may be flooded with rising river waters, resulting in a loss of eggs and young.

Image credit: © Lip Kee Flickr. Some rights reserved.

Emlen (1990, 1991)
Emlen & Wrege (1988, 1991)
Emlen et al (1991)
Fry (2001)
Ryan (2009)
Wrege & Emlen (1991, 1994)