Incubation behaviour of the African jacana

Abstract

In African jacanas all parental care is by males. The male's daytime attendance of the nest (= incubation constancy) averages 53% and is characterized by frequent, short ‘on’ and ‘off shifts in which he leaves the nest, on average, 35 times per day. Ambient temperatures affect both the incubation constancy and the duration of ‘on’ and ‘off’ shifts: on the coldest (x̄ = 22,9°C) of 4 days of variable weather in which egg and ambient temperatures were monitored together with the male's incubation behaviour, the incubation constancy was 70,9%, the eggs were unattended 28,1%, the ‘on’ shifts were long (x̄ = 22,5 min) and the ‘off’ shifts short (x̄ = 8,4 min). In contrast, on the hottest day (x̄ = 31,3°C) the eggs were unattended 56,5% of the day; they were incubated 6,9% and shaded 36,6%. Both ‘on’ (x̄ = 4,7 min) and ‘off’ (x̄ - 6,3 min) shifts were short. At night, when the eggs were constantly incubated, their temperature remained constant at 34,1 °C (SD = 0,4; n = 69) whereas in daytime their temperature ranged between a daily mean of 33,2–37,1°C (n = 4 days) and between extremes of 27,0–39,6°C. On a hot day (x̄ - 30,0°C) when the male was prevented from shading the test egg its temperature reached a lethal level (43,8°C) in 30 min. It is suggested that the high ambient temperatures prevailing in the African jacana's breeding range have facilitated the evolution of a uniparental care system in this species, but the males’ unusual incubation behaviour associated with high temperatures may also have led to the high clutch predation rate found in this species. Onder grootlangtone word die eiers sowel as die kuikens alleen deur die mannetjies uitgebroei en groot- gemaak. Die daaglikse aandag aan die neste (‘broeistandvastigheid’) deur die mannetjies is gemiddeld 53% en word gekenmerk deur baie ‘aan’ en ‘af’ periodes waarvan elkeen van korte duur is. Die mannetjies verlaat die nes gemiddeld 35 keer per dag. Die omringende temperatuur beinvloed beide die broeistandvastighed en die tydsduur van die ‘aan’ en ‘af’ periodes: op die koudste (x̄ = 22,9°C) van vier dae van wisselende weer, toe omringende temperatuur, die temperatuur van die eiers en die mannetjie se broeigedrag aangeteken is, was die broeistandvastigheid 70,9%, die eiers was vir 28,1% van die dag verlate, die ‘aan’ periodes was lank (x̄ = 22,5 min) en die ‘af’ periodes was kort (x̄ = 8,4 min). In teenstelling hiermee was die broeisel op die warmste dag (x̄ = 31,3°C) 56,5% verlate; die mannetjie het vir 6,9% van die dag op die broeisel gesit en dit vir 36,6% in die skadu van sy liggaam gehou. Beide ‘aan‘ (x̄ = 4,7 min) en ‘af’ (x̄ = 6,3 min) periodes was van korte duur. Snags, wanneer daar deurlopend op die eiers gesit was, het die temperatuur van die eiers konstant gebly by 34,1 °C (SD = 0,4; n = 69) maar gedurende die dag het dit gemiddeld tussen 33,2–37,1°C gewissel met uiterstes van 27,0–39,6°C. Op ‘n warm dag, toe die mannetjie verhoed is om die toetseier met sy liggaamskadu te beskerm, het die eier ‘n dodelike temperatuur (43,8°C) in 30 min bereik. Daar word voorgestel dat die hoë omringende temperature wat in die broeigebied van die grootlangtoon voorkom die ewolusie van die versorging van die eiers en kleintjies deur net een ouer vergemaklik het, maar ook dat die buitengewone broeigedrag van die mannetjie gepaard met die hoe temperature, ook tot die hoe predasie- koers van die eiers onder hierdie spesie gelei het