I was riding along the west dyke and spied this dry, brown tangle within the bulrushes. It was about softball-sized, two feet above the mud. It's a Marsh Wren nest, woven from grass and other plant material.
The owner popped up to sing about it. Tek tek tuk tuk zje zje zje zje upty bupty bupty... and so on. For a small bird, the song packs a punch--and is a challenge to syllabify.
Male Marsh Wrens build a dozen or more "dummy" nests within their territories. Favourably impressed females will thus have a number of sites to choose from. Males are polygamous, or want to be, and about half will manage to attract more than one female. Yet still the majority of nests remain unused--as dummies. Presumably they act as decoys to nest-raiding predators.
Some dummies have an additional function. They serve as winter shelters in Marsh Wren populations that don't migrate, including those here in south-western British Columbia. It has been determined that the dummy nests of birds that overwinter in northern latitudes are built more robustly than those of migrant populations.
Not so dumb.