Monarchs can produce four generations during one summer. The first three generations will have life spans from 2 - 6 weeks and will continue moving north. During this time they will mate and have the next generation that will continue the northward migration. The fourth generation is different and can live up to nine months. These are the butterflies that will migrate south for winter to either Mexico or southern California. (source)

Monarchs can travel between 50 - 100 miles a day; it can take up to two months to complete their journey to winter habitats.

Monarchs know when it is time to migrate south for the winter based on the environmental cues associated with seasonal changes. They then get naturally high using air currents and thermals to travel such incredible distances. In fact, the highest monarch was recorded at 11,000 ft by a glider pilot – that’s over two miles up in the air! Just to put this into perspective, most birds fly below 500 ft, hot air balloons only go up about 200 ft, and even songbird migrations occur in the 2000-4000 ft high range. There’s not really much else going on above 11,000 feet other than Mt. Everest (29,028 ft) and passenger jets (36,000 ft). (source)

Monarch butterflies communicate with scents and colors. The males attract females to mate by releasing chemicals from scent glands on the hind wings. Monarchs signal to other animals that they are poisonous by having bright orange wings. The bright colors serve as a warning that predators should attack at their own risk. (source)

Healthy males are more likely to mate than unhealthy ones. Females and males typically mate more than once. Females that mate several times lay more eggs.  Mating for the overwintering populations occurs in the spring, prior to dispersion. Mating is less dependent on pheromones than other species in its genus. (source)