Beyond nest eggs: I and the Bird #33 is up on Don't Mess With Taxes.
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Birds don't live in nests.
Bowerbirds are certainly my favorite examples of animals that build elaborate courtship and mating structures, such as the structure shown below being decorated with blue bottle caps by a male satin bowerbird (image credit: Alan Fear).
Researchers in Florida poured a liquid plaster-metal mixture into the nests of the Florida harvester ant. The resulting casts display astonishing intricacy and depth.