Texas Fall Monarch Flyway Analysis

Texas Monarch Watch

Return to Texas Entomology - Compiled by Mike Quinn

Each fall, the majority of Texas monarch sightings consistently fall into what we call 
the Central and Coastal Flyways.

Central (and larger) Flyway is generally most active from early to late October.

Conversely, the Coastal Flyway is generally active from mid October to mid November.

Question, are these flyways "real" and if so, why the asynchronicity?

Fall Monarch Migration Through Texas Map

Recapping the fall 2007 monarch migration.

Monarchs start heading south in late August.

By the first week in October, monarchs start crossing the Red River

The monarch front appears somewhat asynchronous at this time.

By mid October, monarchs pour through the Central Flyway.

This major monarch migration corridor generally extends from I-35 to Midland.

During the third week of October, the monarch flow appears to shift to the southeast.

At this time, monarchs occupy portions of the Central and Coastal Flyways.

By the last week of October, monarchs are primarily restricted to the Coastal Flyway.

The Coastal Flyway is more variable that the Central Flyway 
and is generally active from mid October to mid November.

The relative lack of monarch watchers across the southeastern U.S. contributes to 
the mystery of the origin of the coastal monarchs, but they likely started in the northeast.

If so, then the greater distance traveled from the northeast might account 
for the asynchronous timing of the Coastal Flyway, 
versus monarchs traveling a shorter distance from the midwest and using the Central Flyway.

If the Coastal Flyway is primarily populated by northeastern originating monarchs,
then a potentially more significant contributing factor to the flyway asynchronicity
is the fact that the wind rarely blows from the NE to the SW so butterflies traveling 
such a route would encounter more cross winds than midwestern originating monarchs.

Some monarchs will overwinter all along the Gulf Coast. 
Is it possible that the impetus to continue migrating is lost due to the lateness of their arrival?

Monarch Roost Maps from Journey North

10 Oct 2009   Mike Quinn / entomike@gmail.com / Texas Entomology / Texas Monarch Watch