Monarch Migration

 

Migration

Why do monarchs migrate and not hibernate?

This is an excellent question! For some reason, monarchs have just not evolved to hibernate. Iit’s a hard question to answer, because we need to know the evolutionary history of monarchs. We are quite sure that the ancestors of monarchs were tropical butterflies that could not survive long periods of very cold weather. When monarchs moved into areas that had cold winters, they never evolved the ability to tolerate these winters, and need to migrate to warmer locations. Many people think that monarchs evolved in the tropics, and just move north each spring to take advantage of all the milkweed we have in the summertime. Most other temperate insects can withstand the freezing temperatures of winter by entering a state called “diapause.” Some do this as eggs, others as larvae, pupae or adults.

How do they travel such far distances?

They are able to travel such far distances by flying very efficiently. They take advantage of air currents and actually soar, like many birds do. This takes much less energy than flapping their wings all the time.

They choose altitudes at which they can take advantage of the wind to help them on their long migratory flights. And they don’t fly when there’s a strong wind blowing in the wrong direction.

They also store up a lot of energy for these long trips. This energy comes from the food they eat as caterpillars, and also from the nectar they get from flowers.

How do monarchs know where to go to overwinter?

We don’t know for sure. We do know that they don’t learn where to go, but instead are genetically programmed to go to the right place at the right time. We also know that they use the sun as a cue to tell them which way is south.

How many miles can monarchs travel in one day?

In general, about 25-30 miles. When weather conditions are favorable, they may be able to go further, but poor weather conditions may also prevent them from traveling at all! Many factors influence how far monarchs can travel in one day, so it is quite variable.

Can butterflies fly in the rain?

No, at least not for long!

How far can one monarch migrate?

It depends on where the migrating monarch starts! Monarchs that develop in areas west of the Rocky Mountains usually do not migrate as far as those east of the Rockies. Rather, these monarchs travel a shorter distance to the Pacific coast of California to overwinter in many sites along the coast.

Monarchs east of the Rocky Mountains can travel up to 3000 miles south to Mexico in order to overwinter. However, only one generation of monarchs undergoes this long journey – those that emerge in late summer and fall. Only those from the northernmost reaches of the breeding grounds travel this far. Others that emerge at lower latitudes during the fall have a shorter distance to travel to reach their overwintering grounds!

What dangers do they face during the migration?

The long journey of the migration comes with many dangers. They rely on good weather to help them make progress in the right direction; strong winds and rains may prevent them from moving, holding them up for days on end. If winds are too strong in one direction, monarchs may not be able to travel as far, if at all. Another weather factor that can impact monarch travel is temperature. If late season temperatures get too cold, monarchs’ flight muscles can’t warm up enough, making it physically impossible for them to fly. Extreme weather events can blow monarchs off course, prevent them from moving forward, or kill them.

Monarchs also require nectar to fuel their flight during the migration. If they are unable to find suitable nectar sources throughout their migratory path, they may die of starvation. They may make it to overwintering grounds, but sometimes they are undernourished when they arrive and could not store enough lipids/fats to survive the winter. It is important that they have access to abundant nectar sources along the way.

Disease can impact the monarch migration. The OE parasite can have a culling effect, meaning that monarchs infected with the parasite may not be strong enough to complete the migration and die on their way.

Other anthropogenic factors, like collisions with vehicles, also pose dangers for migrating monarchs.

Where do they stop along the way?

Monarchs do stop at various locations during their migration. Sometimes they are forced to make pit stops due to adverse weather conditions, but they also stop to rest and refuel at locations with nectar plants available. Monarchs can be sighted on trees in small or large groups as the migration progresses. These roosting sites are where monarchs rest during the migration and can be seen throughout the migratory corridors, though it is hard to predict exactly where they can be seen and when they will be seen there. A few locations in the US, like Cape May, New Jersey, and Peninsula Point, Michigan see more consistent monarch migration movements, since monarchs coming from regions north of those locations funnel through a much smaller area. Monarchs funnel through Texas in large numbers as well, so reports of large migratory movements also come from Texas.

You can follow real-time overnight roost sightings on the Journey North website each fall. See this map from the fall migration of 2013: http://www.learner.org/jnorth/maps/monarch_roosts_fall2013.html