The Figure Below Shows the Results of a Series of Observations

Essay

The figure below shows the results of a series of observations and experiments on tail length in male African widowbirds. The black bars represent manipulated tail lengths by researchers (they actually added length to the tail feathers of the experimental birds). From the black bars on the figure, we see clearly that the male birds that have been artificially manipulated to have super-long tails are very good at attracting mates, approximated by the number of active nests for each male. Why then are the male tails we see in nature (open bars on the figure) so much shorter?