Golf Courses are major Monarch Butterfly Overwintering Sites

[Paul Cherubini]

In recent years monarch butterfly researchers in California have been
finding a surprizing number of overwintering sites on golf courses in
two of the most heavily urbanized parts of the California coast--the San
Francisco Bay Area and Los Angeles Basin.

The phenomenon isn't new, it's just that researchers didn't realize
monarchs would be "attracted" to urban landscapes much less how they
would survive in a polluted environment dominated by asphalt, concrete,
rooftops, cars, buses and airplanes instead of lush rural forests and
meadows.  Researchers also didn't  know exactly where to find monarchs
overwintering in cities. It turns out that ordinary city parks and golf
courses provide sometimes skimpy, but sufficient tree cover to support
substantial overwintering colonies.  Some of these colonies are as large
and persistent as those found in the more rural, densely forested parts
of the coast.

In the San Francisco Bay Area, for example, two large colonies are
located on golf courses in Hayward and San Leandro (between Oakland and
San Jose).  The Sky West Golf Course in Hayward had 60,000 monarchs this
past winter--as large as the world famous colony in Pacific Grove,
Calif.  The San Leandro Marina Golf Course had 30,000 monarchs.Video
footage of the butterflies with golfers teeing off in the background was
broadcast on the CBS evening news with Dan Rather last December. At both
golf courses the butterflies cluster on planted rows of exotic
eucalyptus trees that separate the different fairways (eucalyptus trees
are native to Australia and were introduced to California around 1860).

The lawn of the golf courses is occasionally treated with a tank mixture
of organophosphorous insecticide, a broadleaf herbicide, a high nitrogen
chemical fertilizer and sometimes a lawn fungicide. No one has ever
noticed any adverse effect on the butterflies, but it does raise
questions.

Indeed, the knowledge that monarchs find suitable habitats in urban
locations has prompted researchers to investigate how well the
butterflies survive as compared to monarchs overwintering in more rural
locations.  Last fall, Bobby Gendron and Cassie Smith tagged 1300
monarchs at the San Leandro Golf Course between Sept. 27 and Nov. 2. All
three of us monitored the size of the colony all winter and videotaped
the clusters on several site visits.  We found the colony remained large
and stable up to the third week of February, when the inland spring
migration normally begins. Hundreds of tagged butterflies could be
viewed in the trees throughout the winter and many were involved in the
mass mating "ceremony" that is typical in late February.  These
observations suggested the tagged butterflies had remained healthy
through the winter.

At this point, we wondered how long into the spring the tagged
butterflies would survive.  Over 200,000 monarchs have been tagged at
various colonies up and down the California coast over the past 43
years.  In all these years of research, the latest date that an
overwintered female monarch had ever been recaptured alive was in late
April. The latest date that an overwintered male had ever been
recaptured alive was in early May.

It came as a shock to us to find out the tagged monarchs at the San
Leandro Golf Course monarchs would end up beating all previous records
of longevity.  The first important recapture was made on April 28 when a
tagged female from San Leandro (tagged on Nov. 2) was recaptured alive
while laying eggs on milkweed growing in the backyard of a home in
Paradise, California (110 miles to the NE). This was one of the latest
dates that a tagged, overwintered female monarch had ever been
recaptured.

An even more amazing recovery of another live female (tagged Sept. 27)
was made on May 14 in Sebastopol, California (50 miles to the NNW). 
This butterfly was so old she could barely fly. This is the latest date
(that I am aware of) that a tagged, overwintered female from either
California or Mexico has ever been recaptured alive. And that's after 45
years of tagging around a million monarchs across North America.

Still another surprise recapture was made on June 2, when a male monarch
which had been tagged at the golf course on Sept. 27 was recaptured in
Cloverdale, California, (80 miles to the NNW).  This butterfly was found
dead, but its wings and body parts were still flexible at the time,
suggesting it had died within the past day.  This recapture broke all
previous records too--it is the latest date (that I am aware of) that a
tagged overwintered male monarch from either California or Mexico has
ever been recaptured alive (or nearly alive in this case).

The record late recaptures on April 28, May 14 and June 2 of butterflies
tagged at 
the San Leadro Golf Course, taking together with the videotaped
observations of a stable butterfly population  size through the winter,
has provided the first direct evidence that monarchs have no significant
problems overwintering at this sparsely vegetated, insecticide,
herbicide and chemical fertilizer treated, man made urban overwintering
site, with no understory vegetation, no surrounding forest "buffer" zone
and no nearby nectar filled meadows.

This finding contrasts sharply with the widespread public perception
that overwintering monarchs need a large, dense forest of trees in a
rural setting and a dense and diverse layer of understory vegetation in
order to protect them from winter storm winds, too much light and sun,
freezing temperatures, drying out, bird predators and to conserve their
fat reserves.

Folks reading this may be wondering why the golf course pesticides and
urban air pollution doesn't  seem to harm the butterflies.

With regard to the lawn insecticide, one should consider the target
pest  that the chemical is being directed against--ironically it is
chiefly leps--i.e. lawn moths (in the larval stage). Each insecticide
application kills only about 25-50% of the existing moth larvae
population because only this percentage get a truly  lethal thorough
soaking with the insecticide and there is hardly any residual killing
effect.  Thus, the moth larval population rebuilds after a period of
weeks or months which necessitates re-treatments.  Non-target insects
(like monarchs resting in the trees), not directly hit with the spray
are not noticably affected. And monarchs, like other insects and mammals
have metabolic enzymes that can often quickly detoxify sublethal doses
of harmful man made and natural chemicals they encounter. But
ironically, if well intentioned activists succeeded in banning golf
course pesticides and chemical fertilizers, the golf course would have a
hard time maintaining the grounds and might have to close up shop---and
without golf courses, we would lose some of our best  monarch urban
overwintering habitats.

With regard to air pollution, it appears that monarchs are much like
other butterflies and insects (mourning cloaks, tiger swallowtains,
certain sulfurs, whites and heliconids,  red admirals, etc.) that thrive
in the smoggiest cities (including the parks in Mexico City).

Paul Cherubini, entomologist, El Dorado, California
paulcher at concentric.net