Summary: Incubation and Chicks
Why do birds incubate?
The narrow temperature and hydration tolerances of embryos inside the
eggs demand rigorous attendance by their parents.
Why do not reptiles and fish regularly incubate?
The hormone prolactin mediates the incubation behaviour of birds.
Conversely, the sex hormone testosterone, which mediates aggressive
and sexual behaviour, inhibits the expression of parental behaviour in
birds. Blood levels of testosterone in males birds that incubate drop
sharply after egg laying has begun.
Distribution of different patterns of incubation in 163 families of birds.
Female hornbills (Nashornvögel) lay up to six white eggs in existing
holes in trees or rocks. Before incubation, the females begin to close
the entrance to the nest cavity with a wall made of mud, faeces and
fruit pulp. When the female has laid her eggs, there is only one narrow
aperture, big enough for the male to transfer food to the mother and
the chicks. During the incubation period, the female undergoes a