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_The Megapodes_ 1995 by Jones, Dekker, and Roselaar (Oxford U. Press)
provides support for the following hypotheses.
1. Distribution of nesting strategies is determined by abilities of
predators. Mound-nesting megapodes are susceptible to predation even
though they nest in forest. Predators take cues from the size of the nest
and the constant activities of the parents without whom the embryos would
both cook and suffocate. If non-avian dinosaurs had avian embryonic
growth rates they were likely to have had to stay at the nest!
2. The predation hypothesis is better at explaining the distribution of
megapodes than competition. While some overlap exists between megapodes
and their most similar ecological counterpart (pheasants), almost none
exists between megapodes and carnivorous placental mammals (civets, and
3. Placental carnivores are more efficient plunderers than varanids. A
ref. supplied by above book notes that foxes eat all eggs of the Mallee
fowl nest while varanid lizards give up after a while. The authors
of the _Megapodes_ are mystified as to the evolution of mound-nests from
breeding strategies of other galliforms. Given the fox v. varanid
differences the following hypothesis occurred to me. Megapodes lay their
eggs in a mound as needles in a haystack. Unlike croc eggs they are not
all placed in the same chamber. So, in places that lacked placental
carnivores (assuming they have superior search abilities than varanids) a
megapode strategy might be competitive with that of the concealed
galliform. That is, if varanids are the main predators, the chances are
that at least some of your reproductive effort will not be wasted.
These strands of evidence provide support (support only, mind) for
the following broader hypotheses:
1. With the exception of grass-dependent species (ostrich, rhea, emu)
large birds and large nests are rare today because predators can find
them and destroy them. Placentals are better at locating nests than
varanids and probably marsupials as well. The question is then posed: if
this is true, when did it start being true?
2. The need to ventilate and otherwise attend nests was a cue for Mesozoic
predators of dinosaur eggs. Therefore, defense of nests
was likely a more widely practiced strategy than concealing nests.
3. The extinctions of phorusrhacoid birds with the invasion of mammals 2.5
mya was due to predation by those mammals and not competition with them.
Special thanks to Ron Orenstein for this reference.