Fall Monarch Migration

Fall migration for Monarch butterflies is in full swing! Typically fall migration goes from September to October. Monarchs are the only insect that migrate up to 3,000 miles to find warmer weather. Unlike other insects, monarchs cannot survive the cold winter. The monarchs that are located west of the Rocky Mountains fly to the California coast while the monarchs east of the Rocky Mountains fly farther south to Mexico. The factors that influence the movement of the migration pattern is the shortening of the days and the decrease in the temperature. This diagram represents the direction the monarchs migrate according to their location east and west of the Rocky Mountains.

Monarch butterflies are one of a kind. No other butterfly migrates like the monarchs do. They travel up to 3,000 miles one way and they have a two-way migration every year. They fly in masses to their winter roost and cluster on trees. One monarch weighs less than a gram, but when they cluster together the weight can be enough to break a tree branch. Typically, those heading to Mexico will roost in Oyamel trees. Those heading to California will look for eucalyptus, Monterey pines, and Monterey cypresses to roost in. Monarchs will only travel during  the day and will roost at night. Once they arrive to their roost for the night, they will cluster together to stay warm during the cool, autumn nights. Fir and cedar trees are chosen for roosting because of their thick canopies. The thick canopies will moderate the temperature and humidity of the roost. When morning comes, the monarchs warm themselves in the sunlight before continuing their journey.

The orientation of monarchs is not very well understand and the ability for monarchs to find their roost is a compelling topic. It is thought that monarchs use a combination of directional aids such as the magnetic pull of the earth and the position of the sun to find their location. Monarchs may utilize the angle of the sun along the horizon along with an internal body clock to know where they are going. For example, if their internal clock reads 10:00 a.m., then the monarch will fly to the west of the sun to continue flying south. When their internal clock says noon, they will fly straight towards the sun. Later in the day, the monarch’s instincts will tell them to fly east of the sun. Below is an illustration demonstrating how a monarch utilizes the sun compass for migration.

Migrating monarchs typically have wingspans over 4 inches. On average, they will flap their wings about 5 to 12 times a second. This is about 300-720 times a minute! Monarchs travel between 50-100 miles a day. It can take them up to two month to finish their journey to a warmer climate.