A friend has beautiful zinnias in her garden, so we planted some too this summer, and they are just as beautiful as hers. I noticed, however, that some of them were missing petals, usually on the older flowers with large cones.
Then one morning I noticed one of the blossoms swaying when the others were not. Obviously, this cannot be the wind, I thought. Quick, get the binoculars! Sure enough, that bright yellow was not a zinnia, but a male Goldfinch!
As I observed, he hopped from flower to flower, pulling off petals where necessary to real the small seed at the base of the cone. When zinnia first bloom, the yellow "flowers" look like a crown in the center. The cone grows higher as new "flowers" bloom, while seeds develop from the older ones. The colorful petals have nothing to do with reproduction.
He sure works hard for those small seeds. Goldfinches wait until later in the summer to breed and raise young so seeds will be abundant. Goldfinches are among the strictest vegetarians in the bird world, selecting an entirely vegetable diet and only inadvertently swallowing an occasional insect. Many other seed eaters will feed their young insect, but I couldn't find that these finches do so.
Birds don't weigh much in general, but small songsters must be particularly light-weight, since the flowers bend down only a little when the bird lands on them. I used to get lots of Goldfinches at my feeders, but have seen very few in the last couple of years. Even a new feeder and nyger didn't seem to attract them, so I'm delighted to have them back in the yard, attracted to our flowers.