Complex sentence: The reduction in delivery rate to the polygynously mated females led to a negative effect on their incubation efficiency, because the females needed to spend more time away from the nest acquire food; this also prolonged the incubation period when compared to monogamous females.
Split into simpler sentences: The reduction in delivery rate to the polygynously mated females led to a negative effect on their incubation efficiency, because the females needed to spend more time away from the nest acquiring food. This also prolonged the incubation period when compared to monogamous females.