Setting out a birdfeeder is a common practice in most residential areas. By some estimations, for example, feeders provide nourishment for as many as 30 million birds in Great Britain per year. Despite this fact, however, a scientist in Switzerland has concluded that feeding birds might not be in their best interest. Some male birds, after going without food all night, need to arise early and sing a dawn chorus in order to attract a female. In general, males that sing earliest attract the best mates. When food was introduced overnight, however, 36% of the males didn't start singing until after sunrise, indicating that the well-fed birds became lazy and more ill-prepared to mate and to defend their territories from rivals. According to the passage, which one of the following statements is correct?