The migration of the tired and wary, those seeking refuge from the
hostile world around them has always been a signature hallmark of the
clear and clean waters of Big Spring. Man and beast alike. A shelter from the storms brewing in the outside world.
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| Big Spring in Pleasant Grove |
The Native
Americans drank from the cold water here leaving their stone tools and
weapons behind as evidence. The original European stock pioneers from the earliest
dawning days of the Republic of Texas called it home. On this particular evening in October 2014
the guests are the migrating Monarchs of North America. A sight fewer
and fewer see in Texas as the Monarch population dwindles and their
habitat disappears.
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| The nearby Monarch habitat once covered with Milkweed, destroyed Texas prairie and Post Oak Savannah of the Texas Horse Park for surface mining operations to extract soil for the latest golf course project by the City of Dallas |
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| The everflowing Big Spring in October 2014 in Pleasant Grove, Texas. Part of the Historic Republic of Texas Beeman Land Grant, home of Dallas founder John Neely Bryan and later the Edward Case Pemberton Farm |
As the sun sets in the cooling autumn air of the Great Trinity Forest, migrating Monarch butterflies begin to seek out a suitable roost for the night. Their instinctive migration route, ingrained by tens of thousands of generations of previous monarchs lands them in the sheltering arms of Big Spring and the bows of the Historic Bur Oak and nearby nut bearing pecans and walnuts.
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| Roosting Monarch butterflies on the bowed limbs of a Big Spring pecan tree, directly over the water and head of the spring flows in Pleasant Grove, Texas |
Monarchs and other butterfly species only travel during the day and need to find a roost at night.
Monarchs gather close together during the cool autumn evenings for safety in numbers. These roost
sites are important to the monarch migration. Many of these locations despite the fact that the butterflies have never seen the site
are used year after year. Often densely spaced oaks and cedar trees are chosen for
roosting. These trees have thick canopies that moderate the temperature
and humidity at the roost site. As dawn breaks the next day, monarchs bask in the
sunlight to warm themselves before taking flight.
In all the world, no butterflies migrate like the Monarch butterflies of
North America. They travel much farther than all other tropical
butterflies, up to four thousand miles. They are the only butterfly
species to make such a long, two way migration every year. Amazingly,
they fly in masses to the same winter roosts, often to the exact same
trees.
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| Overflight of Wood Ducks, another migratory species at Big Spring October 2014. Wood Ducks love the old sloughs, oxbows and beaver impounded wetlands in this area. Sadly, their habitat is shrinking by the day here in Pleasant Grove |
The annual Monarch migration is more the type we expect from birds or whales.
However, unlike birds and whales, individuals only make the round-trip
once. It is their children's grandchildren that return south the
following fall. The Monarchs are the only
butterfly that migrates both north and south as the birds do regularly,
but no individual makes the entire round trip, because the migration
period spans the life of three to four generations of the butterfly.
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| As the sun disappears below the horizon, more Monarchs come to roost at Big Spring for the night |
The Monarch butterfly
Danaus plexippus is perhaps the
best known of all North American butterflies. It is easily recognizable
by its bright orange-red wings, with black veins and white spots along
the edges. The Monarch butterfly is famous for its southward migration
from Canada to Mexico and the northward return back through the Great
Plains to Canada in summer. Every fall, millions of these butterflies
fly west to their wintering grounds in California and Mexico, covering
the trees there with their bright shimmering wings.
Their brilliant coloration is mostly for protection
from predators like bats who might not see the bright orange and black
coloration, the tell tale of the bad-tasting and poisonous Monarch. From
the trees beyond the night crew of animals start up their evening
calls. Ready to hunt under a rising crescent moon.
Nectar and Food Corridors
Nectar corridors are a series of habitat patches containing plants
that flower at the appropriate times during the spring and fall
migrations. These patches provide stopping-off points for the migrating
butterflies to refuel and continue their journey. Having these islands
of nectar sources is particularly important within large areas of urban
and agricultural development. The discontinuous patches of nectar
sources are “corridors” that monarchs will follow, like stepping-stones
across a stream to complete their migration.
The Monarchs seen here are consuming nectar from a blooming shrub in the outfall area of Big Spring where water courses down in a gentle meander towards Bryan's Slough. It is
believed that the Monarchs might be following what biologists call a
"nectar corridor" for food. Unknown how the butterflies can find these spots year after year since dozens of generations of butterflies lived, bred and died in the year previous to their last visit.
Monarchs and Milkweed
Many butterflies have a single plant required as a food source for their
larval form called a host plant. Milkweed is the host plant for the
monarch butterfly. Without milkweed, the larva would not be able to
develop into a butterfly.
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| Bumblebee on a Milkweed plant at Big Spring, late Spring 2014 |
The larvae and the butterflies retain poisonous glycosides from their
larval host plant, the milkweed, so they become distasteful to potential
predators. These milkweed butterflies (Monarch, Queen, Soldier) eat
only milkweeds as larvae. This highly effective defense strategy shields
them against almost all predators that soon learn to avoid these
species after attempting to eat them.
Milkweed contains a a variety of chemical compounds that make monarch
caterpillars poisonous to potential predators. Milkweeds contain a
cardiac poison that is poisonous to most vertebrates but does not damage
the monarch caterpillar. Some milkweed species have higher levels of
these toxins than others.
North Texans can attract Monarchs to their backyards by planting
milkweed as a host for Monarch eggs and larvae. Easy to grow here in
Dallas and available as seed or plantings at local native plant sale events.
The Marathon Generation, the special migrators of the Monarch species
As fall approaches non-reproductive monarchs are born. These are the
butterflies that will migrate south. They will not reproduce until the
following spring in 2015. These late summer monarchs will travel hundreds and
even thousands of miles to their winter grounds in Mexico and
California.
They
store fat in their abdomens that will help them make the long trip
south and will help them survive the winter. During their five months in
Mexico from November to May, monarchs remain mostly inactive. They will
remain perfectly still hour-after-hour and day-after-day. They live off
of the stored fat they gained during their fall migration.
Various food sources
The plant they are feeding from in the photo above is known as Roosevelt Willow or Roosevelt Weed
Baccharis neglecta
. It's a tall shrub with many willow-like branches covered with very
dark green, linear leaves. After warm rains in late summer it produces a
profusion of creamy white flower clusters which are followed by silvery
plumed seeds that cover the plant with a white cloud. It grows from
North Carolina to Arizona, and throughout Texas. Roosevelt Willow/Weed
is one of the first plants to invade abandoned fields, roadsides and
disturbed habitats. It is extremely drought tolerant, accepting wet or
dry sites, and can grow in soils high in salt. The historical references
of its common names purportedly come from the fact that after the great
Dust Bowl, it was planted as a fast and easy way to revegetate the
severely damaged soil.
Monarch Migration South Through Texas
The Monarch migration usually starts around October each year, but can
start earlier if the weather turns cold sooner. They travel between
1,500 and 3,800 miles or more from Canada to central Mexican forests
where the climate is warm. If the monarch lives in the Eastern states,
usually east of the Rocky Mountains, it will migrate to Mexico and
hibernate in Oyamel fir trees. If the monarch butterfly lives west of
the Rocky Mountains, it will hibernate in and around Pacific Grove,
California in eucalyptus trees.
Monarch butterflies use the very same
trees each and every year when they migrate, which seems odd because
they aren’t the same butterflies that were there last year. How the
species manages to return to the same overwintering spots over a gap of
several generations is still a subject of research. Some believe the
flight pattern is inherited. Other researches indicate the butterflies
navigate using a combination of the position of the sun in the sky and
the earth's magnetic field for orientation.
The Monarch butterflies migrating through Texas all seem to focus and
funnel into a 50 mile gap between Del Rio and Eagle Pass along the
US-Mexico Border. Here they have a clear route through mountain passes
to the Mexican Interior and highlands.
When they
first arrive at their winter locations in November monarchs gather into
clusters in the trees. These butterflies congregate into colonies, clustering onto pine and
evergreen trees. In many cases, they are so thick that the trees turn
orange in color and branches sag from the weight. It’s a remarkable
sight that attracts scores of tourists.
By December and January, when the weather is at
its coldest, the monarchs will be tightly packed into dense clusters of
hundreds or even thousands of butterflies. By mid-February these
clusters of butterflies begin to break up and the monarchs will begin to
gather nectar. In the spring they will reproduce and their offspring
will make the return trip to the north.
Saving The Future Of Texas Monarchs
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| Master Naturalist Richard Grayson at Big Spring |
The race is on to save what native Texas plant species can be salvaged from current surface mining activities at the Texas Horse Park. The local chapter of North Texas Master Naturalists has been flagging and removing scores of milkweed plants from this area with the hopes of transplanting them at Big Spring in the Fall of 2015. A great article by Roy Appleton of the Dallas Morning News can be found here
http://www.dallasnews.com/news/metro/20140930-naturalists-dig-in-to-save-vegetation-in-the-great-trinity-forest.ece that chronicles the events to salvage what can be saved from that area.
