Crime of Passion (video)

Naughty male Australian satin bower bird selectively steals blue items to decorate his nest. The female bower birds rate their partner by their home decor so they do a lot of stealing.

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Why just blue items? If the female bird rates on taste, wouldn't a mix of colors be better? Blue stands out pretty well against the browns and greens of trees, so why not add reds, pinks, and whatnot to the mix?