Hi members,
I do realise much has been said already, but there's some great relevant
work done on kookas and other birds.
The guest narrator for that section of the program was Andrew Cockburn
from ANU. Working with Sarah Legge, much of the behavioural ecology of
kookas has been nicely described. It seems that while many birds do fool
around quite a bit, laughing kookaburras are among the most 'hi fi' of all
birds examined so far, with almost all chicks (>99%) sired by the alpha
male.
With respect to siblicide, it was reported in a third of nests, with
starvation of the youngest, smallest chick occurring later in about one
fifth of nests.
In terms of hatching at different times (hatching asynchrony), it's not
just that the 1st-laid egg hatches 1st, though this does happen often. The
determining factor seems to be when adult/s begin incubation. Most birds
lay an egg about every 24h, and may start incubating at any stage prior to
clutch completion. This varies between species, and individuals within a
species. A common pattern in passerines is to start full incubation after
laying the penultimate egg. In these cases, most eggs might hatch at about
the same time (within 24h), with a final egg hatching to produce a 'runt'
chick that starts with a size disadvantage that it's often lumped with
until fledging should it survive that long. This is very common in birds,
and one of the best explanations was supplied by David Lack in 1968. He
suggested that given an unpredictable food supply during egg laying,
females should lay an optimistic clutch. If resources prove scarce,
parents can reduce the brood size to fit resource availability, through
the death of the smallest chicks, which carry the lowest levels of prior
parental investment. This, I think, is still a favoured argument.
Stay well,
Iain
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