Monarch butterfly populations markedly down

Here's the sad news reported in Canada's Globe and Mail several weeks ago:

The number of monarch butterflies in the Mexican colonies where the colourful orange and black migratory insects spend their winters has declined to the lowest on record.

The colony size totals only 1.92 hectares this winter, the equivalent of about 2½ soccer fields, compared with the previous low in 2004 of 2.19 hectares, according to the latest Mexican census.

Although the slippage between the two years is slight and is being attributed mainly to weather-related factors last year, biologists and butterfly watchers have been alarmed by the trend to significantly smaller colonies. In the 1990s, monarchs occupied an average of about nine hectares of forests each winter, but for the 10 years ended in 2009 the size had fallen to less than five hectares, according to figures issued by researchers at the University of Kansas.

One problem is that the Mexican overwintering site has been subjected to deforestation, both illegal and also necessitated by a bark beetle infestation.

A second problem this past year was unusually bad (cold, wet) weather in the United States.  This is discussed in an article at MonarchWatch.

But the largest long-term problem is loss of host plants (milkweed) for the caterpillars and food plants (flowering nectar-producing wildflowers) for the adults.

Rural land is also being converted to urban development, and once-idled farmland that may have hosted milkweed plants is being returning to production to take advantage of the demand for corn and soybean biofuel...

TYWKIWDBI encourages the planting of "butterfly gardens" and the protection of wild milkweed wherever possible.  Those interested in monarchs or butterflies in general are encouraged to join the Butterfly Garden forum at GardenWeb (or just read the forum posts there).