[Pollinator] Size of Overwintering Monarch Population in Mexico

[ladadams at aol.com]

Last evening I received the WWFMexico report on the number and sizes 
of  the monarch overwintering colonies in Mexcio. I wish to thank 
Eduardo Rendon  for providing this information. The report (in 
Spanish) can be found at:  
http://www.wwf.org.mx/wwfmex/publicaciones.php?tipo=reps&p=bm.

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.

In a posting to the Monarch Watch Blog on the 20th of October  
(http://monarchwatch.org/blog/2009/10/monarch-population-status-5/) I  
summarized the conditions monarchs confronted during the breeding 
season  and predicted that: "the total hectares will be in the range 
of 2 to 3.5  when all colonies are measured in December." More 
recently, based on the  relative success of taggers this fall, I was 
anticipating that the total  hectares would be closer to 3 hectares. 
Unfortunately, the final number is  below my most pessimistic 
expectation.

As many of you know my  predictions are based on a combination of 
interpretations of the effects of  temperature on monarch populations, 
observations reported to us throughout  the breeding season and early 
in the migration and experience. Of these,  temperatures are the best 
predictor.

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.

I have a pdf of the WWFMx report and will be glad to send it  to those 
who are interested.





-- 
Monarch  Watch
monarch at ku.edu
http://www.MonarchWatch.org/
Dplex-L:  send  message "info Dplex-L" to Listproc at ku.edu
1-888-TAGGING (toll-free!) -or-  1-785-864 4441
University of Kansas
1200 Sunnyside Avenue
Lawrence, KS  66045-7534
Create, Conserve and Protect Monarch Habitats
 





Laurie Davies Adams
Executive  Director
Pollinator Partnership 
423 Washington Street, 5th  floor
San Francisco, CA  94111
415-362-1137
LDA at pollinator.org

_www.pollinator.org_ (http://www.pollinator.org/) 

_www.nappc.org_ (http://www.nappc.org/) 

National Pollinator Week is June 21-27, 2010. 
Beecome  involved at _www.pollinator.org_ (http://www.pollinator.org/) 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sonic.net/pipermail/pollinator/attachments/20100119/08b735e1/attachment.html>