Fall Monarch Population and Migration

Although the number of monarchs at the overwintering sites in Mexico last winter was the lowest yet to be recorded (28.3 million) and the number of females that survived to reproduce this spring in the southern states was quite low, the monarch population appears to have made a remarkable recovery over the last 5 months. Reports from throughout the breeding range indicate the migratory population this fall will be much larger than that of 2000 and it may exceed the population in 1999 and perhaps even the population in 1997. In recent days large numbers of clustered monarchs have been reported from Winnipeg, northern Michigan and west central Wisconsin. The butterflies in Winnipeg should have already begun moving southward and the migration will begin in areas north of 45 degrees in the next week.

If you want to determine the approximate time for the migration to begin in your area, visit

susdesign.com/sunangle/
binary-options-demo.org

Follow the instructions on the site and enter your latitude, date, time (12:01PM), and time zone (for the central time zone use “F” (GMT+6:00)) and time basis (solar). If you don’t know your latitude, go to www.indo.com/distance/ and type in the name of the nearest city. For example, for Winnipeg (49:54 N) the altitude angle for today (17 August) is 53.76 degrees.

Generally, the migration starts close to when the AA reaches 56 degrees and peaks when the AA reaches 52 degrees. Most monarchs leave a particular latitude by the time the AA of the receding fall sun has reached 47 degrees. The interval, or migration window, defined by 56-47 is about 3.5 weeks. For example, in Lawrence, KS the first wave of the migration usually arrives on the 10-11th of September and the peak is near the 20th (AA = 52.39) with all but the last few migrants gone by the 4th of October (AA = 46.95).

Dana Leaving Monarch Watch

If you have had any contact with Monarch Watch over the last 4 years, odds are you know who Dana is (or at least recognize the name ;-). This is Dana’s final week at Monarch Watch as she will be attending her first semester of Veterinary School this fall. Dana’s “formal” farewell will appear in the 2000 Season Summary which will be published later this summer. We’ll all miss Dana but wish her well in her studies.

Monarch Watch Funding

Monarch Watch continues to be financially challenged. We are just scraping by and are still searching for corporate or foundation support. Due to a shortfall in income we are attempting to enlarge our base of support through collaborative arrangements with other organizations. Any leads for potential sources of funding you can provide will be greatly appreciated!

Late Summer Monarchs

Please report all sightings of monarchs seen in August and mid September at latitudes of 38 degrees or less to Monarch Watch. A recent paper by Bill Calvert, personal observations, and numerous previous reports to Dplex-L suggest that reproductive monarchs begin moving south in early August – effectively recolonizing areas devoid of monarchs from mid May to late summer. We need locations and dates of any sightings below 38 degrees (areas south of a “line” from mid KS east to the coast). These data will be used to test a new theory concerning the migration.

Monarch Meeting a Success!

The Monarch Population Dynamics Meeting hosted by Monarch Watch at the University of Kansas from 20-23 May was a great success. We anticipated a meeting with 20 speakers and perhaps 40-50 attendees. Instead, there were 31 speakers (about 11 hours of talks in total), 8 posters (seven of which were presented by students), and a total of 90 attendees.

A detailed account of this meeting will appear in the 2000 Season Summary which will be published later this summer.

Sad News

On the 13th of May, 23 year-old KU senior Shannon Martin was murdered while in Golfito, Costa Rica doing research. Shannon had worked in the Monarch Watch lab for 6 months and and was about to graduate with honors. She spent a semester in Costa Rica last year with KU’s Study Abroad Program and returned for a week last month to collect additional plant samples for her research. Shannon’s work will be completed by her advisor, Dr. Craig Martin (no relation). Shannon was a very positive and responsible person with a promising future in plant biology. She will be missed by all of us.

Lawrence Journal-World articles

Obituary in the Topeka Capital-Journal

Monarch Population Down?

The overwintering monarch population in Mexico was the lowest (2.83 hectares) yet recorded by Eligio Garcia for all overwintering colonies combined. If we use the number of monarchs per hectare suggested by Bill Calvert at the recent meeting in Lawrence (10 million) this means the overwintering population numbered roughly 28 million. Given that approximately half of the monarchs die during the winter and many more die on the way north before they have an opportunity to lay eggs, the number of female monarchs entering the US in March may have been in the range of 5-6 million.

The question is: Is this a sufficient number of females to result in a recovery of the population to normal levels (roughly 60 million) this breeding season? The answer is: Maybe! It depends on how successful the monarchs are in reproducing over the next three months.

Fortunately, even though the arrival of the monarchs was delayed in Texas and throughout the country, the rains of the previous fall, winter and early spring in Texas provided excellent conditions for milkweed and nectar resources for the breeding monarchs. Each year the key to the rest of the season often seems to be the reproductive success of the first generation. This year the reproduction seems to have been better than usual. Good numbers of monarchs have been seen moving northward through eastern Kansas since mid May and this movement has continued into June. More importantly monarchs arrived in the northern states in mid May and good numbers of eggs have been reported in a number of locations. At this point, the prospects are good for a fall population that will be larger than that of the drought-plagued 2000 season.

A chance meeting and perhaps some insights on the spring migration

Note: the following posting was originally sent by Chip Taylor via Monarch Watch’s Dplex-L email discussion list on 1 May 2000.

Yesterday (Sunday 30 April 2000), while visiting the Baker Wetlands in south Lawrence with David Gibo, I stopped to chat with Lexie Powell, an avid birder who has tagged with Monarch Watch. I asked Lexie if he had seen any monarchs and he replied that he had seen 20-30 the previous day. We were astounded. I had only seen one monarch this year (12 April) and had yet to find eggs even though Steve Case had found eggs on his milkweeds a few miles to the NW of Lawrence.

Naturally, we wanted to know where Lexie had seen these monarchs and he directed us to a hilltop cemetery south of Lone Star Lake (SW of Lawrence). Lexie reported seeing monarchs roosting in the tall pines and junipers at the cemetery. This sounded plausible so we obtained directions and reached the location in mid-morning. Sure enough, the monarchs were there. We managed to collect 4, three males and one female while they visited dandelions for nectar. The monarchs appeared to be moving through the area in mid-day. Photos of each of the monarchs can be viewed at the link below.

One question I have raised in the past concerns the sex ratio of the monarchs that reach the limits of the northward migration for the overwintering generation. I knew that males reached KS but I had never seen enough of the worn and tattered migrants to get a sense of the proportion of males that reach this latitude (39N). During two visits at the cemetery yesterday, we observed 15-20 monarchs. Two of these were females but, judging by their flight behavior and coloration, the majority appeared to be males. Clearly, males are dispersing northward in significant numbers along with females.

Although, one or two of the monarchs appeared to be “bright”, including the last one in the picture series below, all had the appearance of the “brownish orange” that typifies overwintering monarchs. If you look closely at this last monarch, you will see many scratches on the wings typical of older monarchs – even though this specimen appears to be in relatively good condition. It wouldn’t be surprising to see new monarchs from Texas by this date but doesn’t seem likely that any of the monarchs we saw originated in the US this spring. (The images are not quite color true. There is more blue in these images than in real life and the oranges are browner than they appear here).

As we left the site, I spotted some milkweeds growing up through the gravel of the roadbed. We stopped to check for eggs and larvae and were surprised to find large numbers of small larvae in the whorled leaves of the meristem at the top of many plants. One shoot had 8 larvae and another had five. Judging by the size of the larvae, some had just entered the third instar, and, given the recent temperatures and consequent developmental rates for eggs and larvae, most of the oviposition to produce these larvae occurred 9-15 days earlier (15-20 April).

I decided to collect a few of the larvae and quickly discovered that I wasn’t the only collector. Ants and lady bird beetle larvae were busy feeding themselves on the monarch larvae and green aphids on the milkweeds. An ant with a young third instar larva is shown in two of the photos. The ants were beginning to patrol many of the milkweeds and it quickly became clear that if I didn’t harvest the larvae, the ants would do so shortly. It appeared that they had already removed larvae from a number of the plants. I collected approximately 50 larvae.

The lesson in all of this might be the hill. The monarchs appeared to be hilltopping and orienting to the tall pines and junipers in the cemetery. The trees formed an arc to the west in a manner that allowed the butterflies to sun themselves late in the day. In spite of being at the top of the hill, there were several areas that were relatively protected from the sweep of the wind. We visited the site again this evening and there were at least 4 worn monarchs – probably all males – sunning themselves in the trees at heights of 12-35′. David pointed out that hilltopping is consistent with migratory behavior in the fall. In fact, Lexie mentioned that the concentrations of monarchs in these same trees in the fall exceeds anything he has seen elsewhere in eastern KS. Although hilltops appear to be risky sites from the standpoint of storms and high winds, they would have the effect of protecting the monarchs from frosts in the fall as well as the spring. Perhaps when looking for early fall and spring concentrations of monarchs, we should give more consideration to hilltops.

Chip

MALE MONARCH, 56 mm
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FEMALE MONARCH, 52 mm
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MALE MONARCH, 57-58 mm
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MALE MONARCH, 54 mm
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Larvae in whorled leaves of meristem
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An ant with young 3rd instar monarch larva
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All Photos: monarchwatch.org/chip/monarchs