RPT-Monarch butterfly numbers flutter up, but still off recent highs -study

(Repeating with no changes to the text.)
By Jon Herskovitz
AUSTIN, Texas, Feb 18 (Reuters) - Favorable weather
conditions at breeding grounds for monarch butterflies in Mexico
are expected to help raise their numbers to possibly more than
100 million this year, about triple of a few years ago, a study
released on Thursday said.
But the overall number of the majestic orange and black
butterflies that travel thousands of miles (km) on a migration
into the United States and Canada is still well below the 1
billion range of two decades ago, the study from a Texas A&M
University researcher said.
"It seems conditions have been successful for monarchs
overwintering - not too wet or cold, which can be a lethal
combination for them," said Craig Wilson, a senior research
associate at the university in the Center for Mathematics and
Education.
The butterflies have suffered from the expansion of
farmland, sprawling housing developments and the clear-cutting
of natural landscapes along their migration path.
Monarchs lay eggs only on milkweed plants, which grow wild
throughout the United States. But the milkweed, on which their
larvae feed, can cause stomach problems for cattle that eat it,
so ranchers and farmers destroy it.
The butterflies breed in Mexico and then have three more
generations as they travel north to Canada.
Millions of butterflies fly en masse, often alighting on the
same trees their grandparents used.
"There are new programs to establish milkweed planting, and
the public is urged very much to do so. The monarch's survival
depends on it," Wilson said.
The insects' plight has become an international issue. In
February 2014, the United States, Mexico and Canada agreed to
set up a joint task force to protect the butterflies.
While an estimated 1 billion monarchs migrated in 1996, only
about 35 million made the trip in 2013, according to Marcus
Kronforst, a professor of ecology and evolution at the
University of Chicago who has studied monarchs.