posted on September 04, 2009 12:43
September monarch migration a harbinger of autumn
PRATT — September is the month to watch for masses of migrating monarch butterflies in Kansas. The weather has cooled, and many people are seeing this regal butterfly in backyards, parks, and in the field. A familiar and popular insect species, monarch migratory behavior is much like that of birds. Navigating on instinct, every monarch east of the Rocky Mountains flies toward a specific area of central Mexico to spend the winter.
Several generations separate the southward-migrating monarchs from those that flew south the previous year, so they do not have elders to guide them on this 1,000- to 3,000-mile journey. The monarchs that live north of Kansas begin moving south in late August. The trigger for their trek south is thought to be the declining angle of the sun as the days get shorter, and this "sun compass" also guides them as they travel.
As the migrating monarchs progress south, local monarchs join them, making the group larger. The observed peak for the Topeka-Kansas City area typically falls about the second or third week in September. The peak for the Wichita area may be a week or so later. On the right day in the right location, careful observers may see hundreds or even thousands of monarchs moving in a south-southwesterly direction on their journey to Mexico. During resting periods, tree branches may be so loaded with monarchs that branches bow and appear almost completely orange. Those lucky enough to have seen this display have witnessed one of nature's marvels.
However, don't expect to see such gatherings in the same place every year. Monarch movement is strongly affected by prevailing weather patterns, so their migration routes vary annually. A good way to attract monarchs and help them refuel on their fall migration is to plant September-blooming plants around home. Asters, sunflowers, goldenrod, and sedum provide blossoms with nectar monarchs need.
The right habitat nearby may even attract overnight roosts of monarchs. They cease flying in the evening and look for sheltered sites in trees to cluster together for the night. These sites often have an easterly exposure, so the monarchs can warm up quickly in the morning sun and resume migration. Such overnight roosts are, in miniature, just like what may be seen at their over-wintering site in Mexico, where acres of trees are so blanketed with butterflies that the branches of trees bend low with their weight.
Monarchs head back north again in March, but they are seldom the same ones that went south the previous September. Rather it is the first generation of their descendants, and they begin arriving around the second week of April. Nor are those that begin the migration the same butterflies that complete the spring migration. Spring migrating monarchs may only fly a few hundred miles, then lay eggs and die. These eggs hatch into caterpillars, pupate, complete the metamorphosis into butterflies, and continue the migration. Thus, the spring migration is often a leapfrog of generations moving as far north as Canada. Some may end their northward migration in Kansas, as well, laying eggs and producing more monarchs throughout the summer that stay in the Sunflower State.
Because the spring flight north is a dispersal with the purpose of laying eggs on newly emerging milkweed rather than the mass retreat from winter that occurs in the fall, large numbers of monarchs are not seen in spring.
For more information on monarch butterflies, including where to look for monarchs and their amazing migration, contact the Monarch Watch program at the University of Kansas online at at www.monarchwatch.org.