From a materials science point of view, here's what I think:
Soil is essentially a ceramic broken down into very small parts. Most
ceramic products don't form a cohesive structure; they are a
collection of individual components with a varying degree of
cross-connection. The harder the components and the more the
inter-connections, the stronger the material. In some applicaitons
(say making a ceramic toilet) the degree of inter-connectedness is
enhanced by firing the ceramic and making more inter-connections. The
Pee-Wees get small bits of mud and put them together, which then dry
forming these connections. More layers are added and the nests get
bigger. Very much like a toilet.
The major governing factor for ceramic strength is the input energy;
ie more energy input into the manufacture (say firing at 150deg vs
4500 for advanced Space Shuttle tiles) equals more strength of the
final product. So I predict that a Pee-Wee nest, built during a humid
period (to help mobilise the bonding agents) and then subject to a
long period of high heat/low humidity/sunlight would last longer that
is rained on earlier in it's lifetime. I further predict that through
natural selection Pee-Wees (and other mud-nest builders) will
eventually learn how to make and control fire, purely for the extra
strength imparted to their nests. However, due to the time frames
involved this will be extremely difficult to prove.
Evan
On 3/8/07, Philip Veerman <> wrote:
A good question (that probably also applies to choughs and apostlebirds), I
would think that sometimes they do break up in heavy rain. However I haven't
seen it happen within the one breeding season from when they are built.
Sometimes they last a whole year but I don't recall that nest often last beyond
that. Inevitably they all break down. Do they do ongoing repair whilst they
have eggs or chicks in the nest? I would think the mud is so tight packed and
fairly smooth surface and that being high in trees, most water would run off or
evaporate before it would severely damage the nest.
Philip
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