Natural selection favors individual birds that achieve the greatest lifetime reproductive success. Finding a prime mate is the first and critical step toward success. Different investments into annual reproductive efforts then add to the diverse life histories of birds. Some birds lay many eggs, whereas, others lay just one. Also, some birds typically live for decades and others for just two or three years. To maximize their contributions to the next generation, individual birds must achieve optimal combinations of variables that affect their lifetime reproduction output.
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