>Monarch Watch Update - February 21, 2002
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>    1) Welcome!
>    2) Adopt-a-Classroom Trip
>    3) Status of the Population
>    4) "Genetic Memory" of the Overwintering Sites?
>    5) Monarch Population Crashes and Recoveries
>    6) How to Unsubscribe from this Update
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>2) Adopt-a-Classroom Trip
>This month's update is short and sweet as we are frantically trying
>to finalize our trip to Mexico. There are still lots of hoops to jump
>through but if all goes well, we should be able to give you a
>preliminary report of the Adopt-a-Classroom / Tag Recovery trip in
>the March update.
>We would like to thank all of you who have made contributions to our
>Adopt-a-Classroom program to aid the schools in Mexico and to those
>of you who have contributed to the Tag Recovery Fund.
>Wish us luck and stay tuned! ;-)
>3) Status of the Population - by Chip Taylor
>Last month I emphasized that all dire predictions about the size of
>the overwintering population were wrong and that preliminary
>indications were that the population was neither as low as the all
>time low (2.83 hectares) nor as high as the population measured last
>winter (9.35 hectares). This year Marco Bernal, Bill Calvert, Isabel
>Ramirez, Jose Maria Suarez, and Lincoln Brower measured the colonies.
>Marco Bernal is the new director of the Monarch Reserve. The total
>area for all colonies was 7.54 hectares. This is lower than the
>average of 9.6 hectares for all sites from 1993-2001 and is the
>fourth lowest population observed over the last 10 years, other low
>populations being 97-98 (5.77), 98-99 (5.56) and 00-01 (2.83). (The
>total for 93-94 was 6.23 but adjusting for the colonies not measured
>that year gives a total of 7.75 hectares. The rational for this
>adjustment is given in the upcoming Season Summary).
>Location / Trees per Hectare / Basal Area / Hectares with Monarchs
>San Andres / 331.44 / 3.08 / .1116
>El Rosario / 63.53* / 4.72 / 4.3313
>Chincua / 580.20 / 43.31 / 1.5908
>La Mesa / -- / -- / .0921
>Pelon - G / -- / -- / .2578
>Pelon - D / -- / -- / .6177
>Oxtotilpan / 302.69 / 19.80 / .0838
>Palomas / 504.90 / 38.61 / .1116
>Piedra Herrada / 226.77 / 14.49 / .1672
>Mil Cumbres / -- / -- / .1747
>Total hectares with monarchs: 7.54 ha**
>*This figure appears to be in error. At the time of measurement, the
>colony at El Rosario was located in a relatively mature but thin
>stand of oyamel fir trees but the figure given here is too low to be
>representative of this forest.
>** In a statement released to the press on February 12th by the
>Mexican Commission for Protected Areas, The World Wildlife Fund
>Mexico, and the Monarch Sanctuary Foundation, the total is given as 8
>hectares. No explanation is provided for the increase but El Rosario
>has been difficult to measure this year due to the structure of the
>forest and the scattered nature of the colony. This would appear to
>make the final number for El Rosario to be 4.89 hectares. If 8
>hectares is accepted as the final number, this years' overwintering
>population is the 5th lowest in the last 10 years.
>Last year after the massive winter kill I tried to reconcile the
>differences in the apparent densities of monarchs at Chincua with
>those of El Rosario by comparing the tree densities at each location.
>However, when I converted the number of trees with monarchs at each
>site to the number of trees per hectare, I came up with about 350
>trees per hectare for both sites. This was true of all other
>locations as well and I concluded that the numbers of trees covered
>with monarchs recorded for each site had been estimated based on the
>assumption that the average tree density was 350 per hectare. The
>forests differ substantially among the sites (see Table above) and if
>the sites are to be compared, tree density and mean size of the trees
>has to be established. This year an attempt has been made to count
>the trees and to calculate the mean basal area of the trees at the
>most important sites. The tree measurement used was the diameter at
>breast height (dbh), a standard measure of tree size used in
>forestry. The mean dbh was multiplied by the tree count per hectare
>to give an estimate of the cover provided by the forest. For example,
>a forest with a density of 500 trees per hectare and mean dbh of .4
>meters per tree yields a basal area coverage of 20.0. Young forests
>have high tree densities and low basal areas and mature forests have
>fewer trees with higher basal coverage. A priori, we might speculate
>that mature forests would provide more cover and protection for
>monarchs and that the monarch densities at such sites might be
>higher. However, this relationship has yet to be established.
>Winter is the dry season in central Mexico, but this has been a
>wetter winter than usual. The high moisture levels should be
>beneficial to the monarchs, as they should keep the dust down on the
>trails in the sanctuaries and should allow the farmers in the
>mountains to plant earlier than usual. It may even keep some of the
>loggers out of the forests. Rainfall is only a concern if soaking
>rains are followed by periods of freezing weather. This was the
>scenario that produced the massive winter kill in January of 2002.
>Valentine's Day was just last week, and (coincidentally I'm sure)
>this signals the time that mating activity increases in the colonies.
>Generally, it is the small, worn, males with little fat body that
>begin to mate first. These males tend to mate with some of the
>largest females, but, as I pointed out in the 2000 Season Summary,
>this seems to be due to the lower maneuverability of the large
>females rather than some manifestation of mate selection.
>A portion of the overwintering population should begin to head north
>in the third week of February (weather permitting) with a few of them
>reaching Texas in the first week of March. The major portion of the
>overwintering population leaves the colonies in the first two weeks
>of March.
>I wish to thank Bill Calvert for explaining the procedures used for
>measuring colonies this year.
>4) "Genetic Memory" of the Overwintering Sites?  - by Chip Taylor
>Do monarchs have a "genetic memory" of the overwintering sites in Mexico?
>One of the ongoing debates among some honey bee biologists is whether
>honey bees have a cognitive memory (i.e. a spatial memory) of two or
>more sites that allows them to fly to a new location, to take short
>cuts, or, to take a new route to a familiar site. As humans, we are
>able to visualize images of sites we have visited and to recall the
>routes taken to reach these sites. In addition, we can estimate the
>spatial relationship of several sites to each other and to plot
>courses along routes we've never traveled to reach particular sites
>and even to reach sites we have never visited. We do this often as we
>move about our cities to shop. It isn't possible for monarchs to have
>a cognitive memory of the overwintering sites, or the route to reach
>them, since they have never been there. Each of the monarchs making
>the fall journey is three to five generations removed from the
>population of monarchs that made the trip the previous fall. If there
>is no individual or collective memory, how do monarchs arrive at the
>specific overwintering area - indeed frequently the same sites on
>mountains - in Mexico year after year? One of the ideas offered to
>explain this phenomenon is "genetic memory" - but, what is that? Can
>DNA contain a code for the migration route and the overwintering
>locations in Mexico? No, it can't. DNA codes for the production of
>proteins; so, if the term genetic memory is used, we have to explain
>how the production of proteins could lead to the complex set of
>behaviors that result in specific flight paths and the choice of
>overwintering sites. I'd rather not use the term - I don't think it
>applies and even if it can be used in a more inclusive sense, the use
>of the word "memory" is misleading.
>So, how might we explain how monarchs reach the overwintering sites?
>What sort of default system is involved and what is the role of DNA?
>The production of proteins coded by the DNA results in complex
>behaviors and sensory systems that can detect a large number of
>environmental parameters. The latter include celestial information
>such as the position of the sun, day length, wind speed and
>direction, temperature, humidity, odors, the ability to detect
>longitude and perhaps latitude, and many more. In the fall, newly
>emerged adults acquire environmental information for some
>indeterminate period (an induction period). The information acquired
>through the sensory system results in a multitude of behavioral
>changes that culminate in directional migratory behavior that is
>appropriate for the monarchs' region of origin. The implication here
>is that the environmental signals induce a cascade of reactions
>through the sensory system that activates and inactivates numerous
>genes and that these genes produce the proteins and subsequent
>biosynthesis that give rise to the appropriate behavioral changes.
>This is the simple version, but it leads to the view that if we knew
>what the butterflies perceived and which signals served as triggers
>that resulted in changes in behavior, we could predict the general
>path of a fall migration and the regions in which they would
>overwinter. In other words, if monarchs were introduced to a new
>continent, and we knew their requirements, we could predict the
>direction they would fly and where they would overwinter. This
>applies to Australia and the introduced monarchs in that country show
>patterns of migratory behavior and overwintering similar to that seen
>in the western states and California. But, this is another story;
>let's get back to the default system.
>In the broadest sense, the DNA of the monarchs is interacting with
>the changing environmental signals (the proximate climatic signals,
>biotic signals and even physiography of the landscape) in a manner
>that has the effect of leading or guiding them to the general region
>of the overwintering sites in the fall and back to the breeding
>habitats in the spring. There is no genetic memory for the
>overwintering sites per se. The migration stalls at the overwintering
>sites (19.4 N) because the rate of change of the environmental
>signals cueing the migration becomes exceedingly small at this
>latitude in November. Of course, all these responses to environmental
>signals have been selected for, so, in a general sense, the DNA has
>been fine-tuned and might be said to have a "memory" for the
>environments encountered throughout the migration. However, this is a
>stretch and I would prefer to leave the term genetic memory out of
>the discussion because it doesn't add to our understanding. To
>understand the migration, we need to focus on the process questions.
>What are the environmental signals, how does the butterfly perceive
>and process this information and how do the perceived signals lead to
>physiological, biochemical and behavioral changes which initiate,
>maintain, stop, and then (months later) restart the migration in the
>opposite direction?
>5) Monarch Population Crashes and Recoveries - by Chip Taylor
>The monarch population has crashed and recovered in dramatic fashion
>several times in the last 4 years. The size of the overwintering
>population in 1999-2000, 9.05 hectares, was near normal. In the
>following winter, 2000-2001, the total area was only 2.83 hectares,
>the all-time low for the wintering population early in the season.
>This was an unprecedented crash and it occurred during the summer.
>The explanation appears to be drought. In the spring a drought
>extended from central Mexico into Texas, and later, in early and mid
>summer, it included the mid-west. These conditions were followed by
>extremely dry weather and reduced flowering along much of the
>migratory route in September and October. Overall, this was the
>driest year in the last 11 seasons and monarchs did not do well under
>these conditions.
>During the winter of 2000-2001, there were two events that resulted
>in significant mortality. Early in the winter, the colony at San
>Andres, a severely degraded and poorly protected site, experienced
>temperatures low enough to kill most of the monarchs in that colony.
>Similarly, in the first week of March, high winds, rain, snow, and
>ice reportedly killed most of the monarchs at Cerro Pelon and some of
>the other eastern colonies. The numbers of monarchs killed at Chincua
>and El Rosario at this time were reported to be relatively modest
>(7%). (The mortality of the monarchs at San Andres was originally
>attributed to pesticides used by loggers, but this was subsequently
>shown not to be the case). As a result of these episodes of
>catastrophic mortality, the initial population of 2.83 hectares was
>much diminished by the end of the winter. Unfortunately, there was no
>late winter measurement of the colonies. However, it is likely that
>no more than 2 hectares of butterflies, remained. We had never seen
>such a low population, so the prospects for the next season did not
>look good.
>The monarchs bounced back the following summer and in the winter of
>2001-2002 the population measured 9.35 hectares. This was an
>extraordinary recovery, one that demonstrated the remarkable ability
>of the monarch population to increase under favorable conditions. All
>was well with the wintering population until the storm of 12-16
>January 2002. This storm, which is described in detail on the web
>site, the Season Summary and in press accounts, contributed to the
>deaths of 75-80% of the monarchs at Chincua and El Rosario. The storm
>was widespread, and, if this level of mortality occurred at all
>colonies, the population was once again reduced to approximately 2
>hectares of surviving butterflies. Once again the monarch population
>recovered in the breeding season and this winter the population has
>been estimated to be 8 hectares. The monarchs have been fortunate.
>Two bad winters have been followed by two reasonably good breeding
>seasons in which the populations have been able to increase to nearly
>average numbers. Imagine the outcome if the low overwintering
>populations of the last two years encountered spring, summer, and
>fall conditions similar to those in 2000. The subsequent
>overwintering population would be extremely small.
>We haven't been tracking monarchs long enough to be able to estimate
>the likelihood of low overwintering populations being followed by
>harsh, unfavorable, summers, but this will happen; the question is
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Kent P. McFarland
Conservation Biology Dept.
Vermont Institute of Natural Science
27023 Church Hill Road
Woodstock, VT   05091   USA
802-457-2779 x124