[Pollinator] Western Monarch Population Hanging On

Thu Feb 20 11:20:34 PST 2014

From: Bay Nature

http://baynature.org/articles/monarch-butterfly-populations-hanging/

Western Monarch Population Hanging On

by Alessandra Bergamin <http://baynature.org/author/alessandra/>  on
February 18, 2014

Monarch butterfly populations in California's coastal overwintering sites
showed a slight - and surprising - rebound in 2013 after more than a decade
of dwindling numbers.

The 2013 Western Monarch Thanksgiving Count
<http://www.xerces.org/butterfly-conservation/western-monarch-thanksgiving-c
ount/>  tallied 211,275 monarchs at 162 sites from Sonoma County to San
Diego County, up from 144,812 the year before.

Over the past two decades, the Western Monarch population has dramatically
declined in California and the slight increase in this year's count is an
encouraging sign that the population is hanging on.

"We were bracing ourselves for that downward trend to continue this year,"
said Mia Monroe, a Xerces Society volunteer who coordinates the yearly
count. "So to have the population be a little higher and to have some sites
really holding onto the monarchs is encouraging."

For the Western Monarch Thanksgiving Count, volunteers across the state
meticulously count scores of butterflies for a three-week period around
Thanksgiving. In the Bay Area, about 20 volunteers participated in the 2013
count, Monroe said. The count focuses on the western monarch population,
those west of the Rocky Mountains that overwinter in coastal California. In
the spring, these monarchs will fly east to the Central Valley and the
Sierra Nevada foothills, as well as north to Oregon and Washington, in
search of milkweed on which to lay their eggs.

For the past few years, overwintering sites at the San Leandro Golf course
and Ardenwood Historic Farm <http://www.ebparks.org/parks/ardenwood>  in
Fremont have had relatively stable numbers, with around 5,000 at the golf
course and 1,032 at the farm.

Natural Bridges State Beach <http://www.parks.ca.gov/?page_id=541>  in Santa
Cruz showed the most surprising results this year: In 2012, the number of
monarchs overwintering at Natural Bridges dropped to an all time low of just
500, but this year the number rose to 4,600 monarchs overwintering at the
seaside eucalyptus grove.

"With all the fire and the drought I was really worried that we wouldn't see
so many monarchs this year," said Martha Nitzberg, an interpretive
specialist at Natural Bridges. "We were very pleased that it was a better
population than last year."

Nitzberg said that several changes at the park may have contributed to the
higher number of monarchs overwintering at the grove. In 2012, the park's
scrub-jay population disrupted the monarchs, so much so that few butterflies
stayed for the duration of winter. Since then, staff have re-landscaped
various areas of the park to remove much of the lawn and watering systems,
and perhaps make it less favorable to nesting scrub-jays. Several crows and
an owl, were also seen at the park and may have contributed to the absence
of the jays this year.

While populations at some overwintering sites were up and others were down,
monarchs overall are at a fraction of their historic number. In 1997, the
count's inaugural year, more than 1.2 million monarchs were counted at 101
coastal California sites. By the following year the number had dropped to
just 564,349 butterflies recorded.

Sarina Jepsen, the Xerces Society endangered species program director says
that researchers are still trying to explain the decline, but issues such as
loss of overwintering sites, loss of breeding habitat, the use of
herbicides, and drought have contributed.

"I think that drought is the big one," Jepsen said. "The most research to
date has been done on that, and with climate change models predicting
drought to worsen in the coming decades, that's really concerning."

A study
<http://www.monarch.org.nz/monarch/wp-content/uploads/2010/08/StevensandFrey
.pdf>  by biologists Shawna Stevens and Dennis Frey in 2010 hypothesized
that the increasing severity of drought across the West was correlated with
the decline of monarch populations. Milkweed, the monarch's host plant, is
the only plant a female will lay eggs on and the only plant caterpillars
will eat. A lack of rain has been shown to reduce milkweed biomass and
shorten its summer availability, meaning if it is a particularly dry season
there may be little milkweed available on which a female can lay her eggs.

In the West, monarchs typically migrate around Valentine's Day, Monroe said,
but this year there have been sightings of monarchs mating a month earlier
than usual. This has raised concerns as to whether pregnant females will
find milkweed available in the Santa Clara Valley or the Diablo foothills so
early in the season. While the recent rain has been encouraging, it is too
early to tell whether it will have made any difference for early mating
monarchs.

"To be honest with you, we're in our hold-our-breath mode," Monroe said.
"One of the things about monarchs is they breed not only monarchs, but hope
- and with this rain the hope is that maybe the milkweed will emerge and
maybe we'll luck out."

While the majority of the data for the annual count is collected during the
Thanksgiving period, Monroe encourages volunteers to regularly visit
overwintering sites and track changes - as they did, for example, during the
cold snap in early December.

"Many people went out after the counts and we were reassured that most of
the monarchs had made it through the freeze," she said. "So the protective
quality of the forest did the job."

While California's monarchs may be holding on, a new report
<https://www.dropbox.com/s/8u39useesogel5m/Monarch%20Butterfly%20colonies%20
2013-2014%20Alianza%20WWF-Telcel.docx>  from the World Wildlife Fund
<http://www.wwf.org.mx/>  in Mexico, has found that the number of monarchs
overwintering in Mexico's Oyamel fir forest has reached an all-time low. The
reports suggest that factors such as loss of habitat, climate change and use
of insecticides have contributed to the decline.

While it is largely the eastern population of monarchs - those east of the
Rocky Mountains - that migrates to Mexico, new evidence suggests that
clusters from the western population may also make the long migration. In
Arizona, a group of volunteers <http://www.swmonarchs.org/>  have been
tagging monarchs during the summer to track their migration. While some of
these butterflies have been documented in California, others have been found
in Mexico. Biologists and volunteers are now trying to determine what
factors may cause one monarch to migrate to California and another to
Mexico, Monroe said.

"It shows you just how complex nature is," she said. "The big lesson is,
it's not a simple story."

________

Matthew Shepherd

Communications Director

The Xerces Society for Invertebrate Conservation

Protecting the Life that Sustains Us

628 NE Broadway, Ste 200, Portland, OR 97232-1324, USA

 <mailto:mdshepherd at xerces.org> mdshepherd at xerces.org 

Tel: (503) 232-6639 ext. 110

Toll free: 1-855-232 6639 ext. 110

Cell: (503) 807-1577

Fax: (503) 233-6794

Stay in touch:

 <http://www.xerces.org/> xerces.org
<http://www.facebook.com/pages/The-Xerces-Society/193182577358618> Facebook
<http://www.xerces.org/enewsletters/> E-newsletter
<https://twitter.com/xerces_society> Twitter

The Xerces Society for Invertebrate Conservation is an international
nonprofit organization that protects wildlife through the conservation of
invertebrates and their habitat.

To join the Society, make a donation, or read about our work, please visit
<http://www.xerces.org/> www.xerces.org.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sonic.net/pipermail/pollinator/attachments/20140220/2f012ee3/attachment.html>