Loudoun Wildlife Conservancy

I thought it would be interesting to do a monthly posting on Monarch butterflies: where they are and how they’re doing throughout the year. I’ll apologize in advance for the news in this post because it’s a bit of a downer but hopefully the news of the Monarch populations will improve as we move through the year.

For those who attended my program on Monarchs this past year, you know that they have a pretty interesting lifecycle that takes them through 4 generations of butterflies over the course of the year with the fall generation being the one that makes the epic journey all the way to Mexico! They rely on habitat here and in Mexico and both are under threats of different sorts. That, combined with the usual challenges of weather that they face make the great Monarch migration an endangered phenomenon.

But let’s kick off with catching up with our Monarch friends - those Monarch butterflies that you saw in late August, September and into October flew 2,000 miles to a very special mountain area near the town of Angangueo, Mexico. That is where they are right now: in a tiny mountain forest area outside of Mexico City, at an altitude of around 8,000 feet, clinging to branches of Oyamel pine trees, resting and awaiting the change in season so they can breed and begin the migration back.

Unfortunately, the numbers this year are at an all-time low. The World Wildlife Fund’s Mexico staff have been monitoring the number of monarchs and I saw this report from them posted by Monarch Watch. The places I visited last February and showed in my program were the three colony sanctuaries mentioned in the report below:

“The news is not good. The total area occupied by monarchs at the overwintering sites in December was 1.92 hectares. Only 7 colonies were found. The three largest colonies El Capulin (Cerro Pelon) 0.53ha, El Rosario 0.50ha, and Cerro Prieto (Chincua) 0.47ha constitute 78% of the total area. The totals for both hectares and numbers of colonies are at an all time low.

Good records of the numbers of colonies and area occupied go back to 1992 and there is less complete data for most years going back to the late 1970s and numbers this year appear to be lower than observed for any year since the overwintering colonies became known to science in 1975. The lowest previous total, 2.19 hectares, was reported in 2004.

This decline continues a trend that started in the late 1990s. In the decade of the 90s the mean area occupied by monarch colonies was close to 9 hectares. The mean for the last 10 years, through the 09 migration, is now below 5 hectares per year and the three lowest monarch overwintering populations were reported in this decade.”

Chip Taylor of Monarch Watch offers explanations for the low numbers:

“Without going into great detail and wishing not to repeat the October report, here is a brief summary of the reasons for the low overwintering numbers.

1.) High temperatures in Texas in March and early April limited production of first generation monarchs. It is these monarchs that recolonize the northern breeding range and fewer monarchs moving north/northeast out of Texas from late April to June impacts the rest of the breeding season.

2.) Conditions were less than ideal for the first generation monarchs as they moved north in May and early June.

3.) Upon arrival in Minnesota monarchs encountered drought conditions that limited reproductive success of first generation in that area.

4.) As the summer progressed, cool and cool, rainy conditions prevailed in many areas, limiting reproduction and slowing development of larvae.

5.) Colder than normal condition prevailed for most of the western two thirds of the northern breeding area from mid June into early September.

In many respects the conditions during the monarch breeding season in 2009 were a repeat of the conditions seen in 2004 that contributed to the previous low overwintering population number of 2.19 hectares.

In spite of the recent cold snap that reached into Mexico, there have been no indications of weather related mortality at the overwintering sites. Let’s hope that normal winter conditions prevail during the next 7-8  weeks. Even if there should be some mortality, our experience with the disaster of 2002, in which an estimated 80% of the population died as the result of a January storm, showed that, if at least 1 hectare of monarchs survives to move north and, IF they encounter normal conditions as they move north through Mexico and in Texas, the population can recover.”

Ok, so the news isn’t great this month but there’s the glimmer of hope that Chip offers that the population can recover if they don’t encounter further setbacks. Let’s hope there aren’t any bad cold snaps in Mexico over the next few weeks.

If there is enough interest, I’d be happy to do my program on Monarchs and their lifecycle again this Spring – just let me know.