08 December 2009

Nesting

What is a nest?

Only one living bird does not incubate: AUSTRALIAN MEGAPODES (moundbuilders). They dig pits and throw sand on top. An egg chamber lies on top of pile of organic matter. The fermentation of organic matter produces heat. The megapode can control the temperature of the egg chamber by bringin in new or taking out old organic matter. Is this left over from reptilian ancestry or independent development?

A few birds build no nest, by any definition, nothing. Brood parasites are an example. The Galapagos Albatross and some penguins don't build nests. Fairy Terns lay single egg in a tree fork. The chick is born with oversized feet--if they fall, the parents ignore them.

Most other birds build nests--simple to complex. Complexity proportional to: time investment (= metabolic rate), consciousness (more complex = more conspicuous); and accessibility to predators (the more complex, the more inaccessible)--in areas with few predators = less well hidden.

Nests in the tropics are hidden and better camouflaged. Nests on islands are often conspicuous. Nests often provide protection from weather. In the temperate zone, where it is cold and windy, nests are deeper, thicker, lower in trees (?), In deserts, look for domed nests, few open cups.

Here are the next topics to be covered:
TYPES OF NESTS
COOPERATIVE BREEDING
EGGS
INCUBATION
YOUNG
BREEDING SEASONS

Galapagos Albatross

No comments:

Post a Comment