Complex sentence: Season dates are often timed to occur when the population is at its maximum and to avoid periods of vulnerability, it avoids the peak breeding period when members of a species are particularly vulnerable and avoids any disruption to mating, which may affect productivity.
Split into simpler sentences: Season dates are often timed to occur when the population is at its maximum. It avoids the peak breeding period when members of a species are particularly vulnerable, and avoids any disruption to mating, which may affect productivity.