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MONARCH
BUTTERFLIES ON THE MOVE
By Richard Julian, Director Education
Connecticut
Audubon Coastal Center at Milford Point
Late
summer is a time when many animals are migrating south. Changes
in the amount of daylight and other environmental cues trigger
animals to leave their summer grounds and move to their winter
grounds. One of the more remarkable migrations is that of
the Monarch butterfly, Danaus plexippus.
2,000+
Mile Migration Route
In
July, Monarch butterflies first appear on flowers at Milford
Point and throughout Connecticut. These adults will lay eggs
on milkweed plants. Larval caterpillars will hatch from these
eggs and continue to feed on the milkweed until they metamorphosize
into adult butterflies by late August and September. This
fall population, with luck, will then make the long migration
to Mexico. If they survive the winter in the mountains of
central Mexico, they will fly back north in the early spring.
This
population will then lay eggs on milkweed plants in the southern
mid-west (Texas, Kansas, and neighboring states). It is believed
that from these eggs the next generation of butterflies will
spread throughout the mid-west and eastern United States.
How
do we know this happens? Although Monarch butterflies do not
travel fast, they are difficult to track and their migration
patterns proved a mystery to researchers for years. The key
to our understanding has come from extensive tagging programs.
(see Tagging A Butterfly)
Many
Questions to Answer
In
the 1950’s researchers discovered large populations of Monarch
butterflies spending the winter in the mountains outside of
Mexico City, Mexico. In 1976 a butterfly tagged in Minnesota
confirmed that northern populations of Monarchs migrate to
Mexico. By the early 1990’s tagging efforts by researchers
alone could not generate the amount of data to answer important
questions regarding the population biology of Monarch butterflies.
How large is the overwintering population of Monarchs? Does
it vary from year to year? How do Monarchs navigate during
their migration? How are they affected by wind and weather
during their migration?
In
1992 Dr. Orley “Chip” Taylor of the University of Kansas began
Monarch Watch, a cooperative network of students, teachers,
volunteers and researchers to help answer these questions
regarding Monarch butterfly migration. Now with over 100,000
volunteers throughout the United States, they tag over 70,000
butterflies a year. In 1999, 689 butterflies were recovered
in Mexico, with an additional 62 recovered within the United
States. With this data they have estimated the 1999 overwintering
population to be between 105-110 million butterflies, compared
to the estimated 65-70 million in 1998. Monarch Watch
needs a higher number of recaptures within the United States
to better understand how these butterflies navigate the 2,000+
miles to their wintering grounds.
Monarch
Watch Program at Milford Point
We
began tagging Monarch butterflies at the Connecticut Audubon
Coastal Center in the fall of 1998 (see Tagging A Butterfly).
The previous year, I witnessed a large migration of Monarchs
through the sanctuary and was curious as to their fate. I
learned of Monarch Watch and decided to participate in their
tagging program to help answer some of my questions in addition
to those of the national study. What percentage of the population
from Connecticut actually makes it to their wintering grounds
in Mexico? How far do they travel in a day? Do they use Milford
Point as a staging area before crossing Long Island Sound
or are they following the coastline south?
At
this date, none of the butterflies tagged at Milford Point
have been recovered in Mexico, but other butterflies tagged
in Connecticut have made the journey. So, although Connecticut
is on the eastern edge of Monarchs’ territory, they do make
it to their overwintering site. Of the 216 butterflies tagged
at the Coastal Center in 2000, five have been recaptured,
all from Long Island, NY. In addition, we netted a Monarch
butterfly that was previously tagged in Quebec, released and
recaptured again on Long Island. This suggests that Monarchs
may in fact use Milford Point as a staging area, feeding and
resting before crossing Long Island Sound.
I
was also curious as to how the butterfly population utilizes
the sanctuary at Milford Point. Are there more males than
females? Do they mainly use the sanctuary as a foraging or
roosting site? Are the numbers observed at Milford Point related
to wind and weather patterns?
Having
tagged and released over 400 butterflies in the past two years,
I have discovered some trends.
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More
males than females (about 60/40) were captured.
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Butterflies
were mainly found feeding (about 80%), on Butterfly Bush
and Cosmos in the Coastal Centers butterfly garden, or
on Seaside Goldenrod and asters growing on the sanctuary.
There
is still so much more to do and learn about Monarch butterflies
here at Milford Point and throughout their range. I plan to
tag over 500 butterflies this season, with the hope that at
least one will be recovered in Mexico.
I
also plan to expand the volunteer base to help collect and
tag Monarch butterflies at Milford Point. On Saturday, September
1 at 2:00 PM, I will host a program, Magic of Monarch
Butterflies, at the Coastal Center. Come learn more
about the life history of this butterfly and about other local
butterflies, and learn how you can volunteer and support this
research and education program. Teachers can contact me (Richard
Julian) at 203-878-7440, about school programs that include
tagging Monarchs, incorporating hands-on research into the
education experience.
Tagging
A Butterfly
It is really quite easy!
Butterflies
are collected using a standard aerial sweep net.
They
are gently gathered from the net (holding them by their
closed wings).
A
small mylar tag (about the size of a hole punch) coated
with adhesive is placed on the lower surface of their hind
wing (visible when the butterfly is at rest).
The
animal is sexed and then released.
In
addition to recording the date and location of collection,
how the butterfly was collected (while feeding, while at
rest or while in flight) and the weather conditions (temperature,
wind direction) are noted.
Many
people ask if tagging affects the butterfly’s ability to fly.
After tagging them, I have observed no change in their flying
ability. Monarchs often show signs of wear, such as rips in
their wings and missing scales, yet they still have the ability
to fly. The tags are light and when placed properly in the
center of their hind wing appear not to effect their flight.
Finally, tagged butterflies have been found in Mexico, confirming
that they can complete their long distance migration with
the tag.
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