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Contents:

1) Status of the Population

2) Temperatures During the Migration

3) Tagging Data and Recoveries

4) Tell Us What You Think

5) About Our Update List

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Unless otherwise noted, all content was authored by Chip Taylor, edited by Jim Lovett and Sarah Schmidt, and published by Jim Lovett.

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1) Status of the Population

Written by Chip on 30 October 2005.

Well, it’s another end of the month Sunday and I still don’t have the update completed. I always promise myself I’ll get the update done before the weekend to give myself some time to catch on the work around the house but it just doesn’t happen. Mowing the lawn and cleaning the garage will just have to wait - again. It’s a beautiful day and though we had a killing frost last week, there are still many blooms on the butterfly bushes in the garden. The flowers are covered with late Painted Ladies, American Painted Ladies, Buckeyes, Orange sulfurs, Cloudless sulfurs, and a few skippers. Aside from the skippers, each of these species appears to be moving south. I saw a monarch, too – the first in two weeks. Imagine this – the first monarchs arrive in the vicinity of the overwintering sites during the last few days of October while others, as far as 1400 miles behind the leaders, are still on their way.

The fact is there just isn’t much to say this month. We all know that the monarch migration the past two months has been good. It was not outstanding, but it was quite good. I’m sticking with my earlier prediction that the overwintering population will be 7-9 hectares. Whatever the final numbers, the population has rebounded well from the all time low of 2.17 hectares last winter. If the population winters well and there are no major storms with freezing rain, there could be good numbers of monarchs moving north next spring. We are beginning to get some insights as to what determines the changes in numbers of monarchs from year to year. We expect to have something to say on this issue at the upcoming meeting at California Polytechnic State University (San Luis Obispo) in December.

The datasheets are arriving in our mailbox in good numbers suggesting that taggers did well. Last year the datasheets were just a trickle and a mere 25,000 or so monarchs were tagged, the lowest number since 1995-96:

http://www.monarchwatch.org/update/2005/0728.html#5

In addition, there were numerous reports from Texas, as relayed by Mike Quinn, of clusters and flights of thousands of monarchs. The majority of reports and correspondents extolled the improved migration this year with a number claiming this migration to be one of the best in their experience.

Both September and October have been warmer than usual for most of the central portion of the country. The warm weather may have delayed the migration slightly and warm conditions allowed late emerging monarchs to join the migration. It seems likely that a higher proportion of the late-tagged monarchs will reach the overwintering sites this fall than occurs during most years. The number of late monarchs in Lawrence was extraordinary and they had trouble moving on because of unfavorable winds and low temperatures. At one point, it appeared that these late monarchs had been held up as long as 9 days. Monarchs are usually scarce in the Lawrence area after 4 October with collectable numbers only on big patches of fall asters. This year, monarchs were quite conspicuous, and one might even say abundant, on the flowers around our building well into mid October. In fact, I collected 33 monarchs around the lab on 16-17 October. I saw three monarchs in Washington, D.C. the following week. However, I hadn’t spotted any since my return, even though we’ve had some favorable conditions, until the one I spotted this afternoon.

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2) Temperatures During the Migration

The delayed monarchs I mentioned above led me to ask – what are the average temperature conditions the monarchs encounter during the migration? I don’t have time to explore this question in detail this month, but here are some tidbits to start the discussion. The window for the migration in Lawrence is from the 11th of September to the 4th of October. The mean temperature for this period is 65F. As monarchs move south, they can encounter higher temperatures. Because diapause in monarchs is sensitive to high temperatures, monarchs minimize their activity and seek shade when temperatures high. Some monarchs exposed to prolonged high temperatures become reproductive. These late season reproductives account for some of the egg laying seen in October and November and these butterflies appear to drop out of the migration.

High temperatures in October, especially if accompanied by drought conditions, could certainly contribute to mortality during the migration, but what about cold temperatures? Monarchs migrate through Texas in late September and October. The mean temperatures for October are shown for selected Texas cities in Table 1. The mean temperatures for the northern and western cities, e.g. Abilene, Midland, and San Angelo are similar to those of Lawrence; the others are higher. In general, high temperatures in Texas during the migration would appear to be more of a threat to monarchs than cool temperatures but what happened in 1976? The temperatures in October of 1976 (Table 1) were the lowest recorded from 1895 to the present. In Austin, there were 25 days in which the high temperatures were less than 60 degrees while in an average year, e.g. 2000, there are typically 12 days with temperatures below 60. The mean low in 1976 was 50F and 60 F in 2000. Although monarchs can fly at temperatures in the mid 50s, in unobstructed sunlight and low wind speeds, it appears that most of the long distance movements are achieved when the temperatures are 60F or better. In Austin in 1976, it appears that monarchs only had 5 days in October with favorable conditions. A similar pattern applies to the other cities raising the possibility that a substantial portion of the fall monarch population passing through Texas in 1976 did not reach Mexico. Or did they?

While the fall temperatures in 1976 are a curiosity, they are also of historical interest. In early January and February of 1975, Ken and Cathy Brugger were led to two distinct monarch colonies, Cerro Pelon and Sierra Chincua. These were the first monarch colonies to become known to scientists and Sierra Chincua was circumspectly described by Dr. Fred Urquhart in an article in the August 1976 (Volume 150 No. 2) issue of National Geographic Magazine. The first attempt to measure the size of the overwintering monarch colony was made in 1976 by Calvert and Brower (1986). The total area was estimated to be 1.5 hectares. Since 1993, the size of the colony(ies) at Sierra Chincua has ranged from .24 to 6.85 hectares with a mean of 2.50 hectares. There is no suggestion in the data over the last 12 years that the colonies at Chincua have consistently increased or decreased in total. Thus, it would appear that the number of butterflies at Chincua was lower than normal in 1976. Could this low number have been due to the cold October in Texas? Maybe, but only in part since there are certainly other factors that determine the numbers of overwintering monarchs.

Table 1. Mean October temperatures for selected cities located along the main monarch corridor through Texas. The temperatures in October of 1976, the lowest recorded from 1895-2004, may have restricted the movement of monarchs through the state on their way to Mexico. Data assembled by Janis Lentz.

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3) Tagging Data and Recoveries

As mentioned above, we are receiving a steady stream of datasheets in the mail - if you haven't made copies of your sheets and sent us the originals yet please do so soon. All data will be entered into a database so that it will be at our fingertips once we start retrieve the tag data from recoveries in Mexico next year.

Just as a reminder, we will not receive the bulk of the recoveries until March so there won't be many additions to the Online Recovery Database until we have processed them (by April or May). In the meantime though please feel free to take the existing Database search (10,000+ tag recoveries) for a spin and let us know what you think:

http://www.monarchwatch.org/tagmig/recoveries.htm

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4) Tell Us What You Think

We'd love to get more feedback from the 1,000s (tens of 1,000s?) of Monarch Watchers out there - on any aspect of our program that you'd like to address (web site, forums, email lists, rearing program, tagging program, Monarch Waystation program, Monarch Watch Shop, whatever! You can of course always drop us a line via email (monarch@ku.edu) but if you haven't already checked out our online community forums I'll invite you to provide your feedback there. It only takes a few minutes to register and you can begin posting immediately (there is a forum specifically for your Suggestions and Comments).

There are currently 467 registered users of the Monarch Watch Forums, representing at least 9 countries - they come from all walks of life and are anxious to share their experiences and hear from other Monarch Watchers around the globe. This is YOUR space so we need to know what we can do to improve it and make it a wonderful place to visit. Browse the forum messages at your leisure and post your comments at

http://www.MonarchWatch.org/forums/

If you have any questions about this please feel free to drop us a line anytime - thanks!

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5) About Our Update List

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