==========================================

Contents:

1) Status of the Population

2) Degree Days Again!

3) Monarch Waystation Update

4) Monarch Tag Recoveries

5) Monarch Rearing Containers

6) Milkweed Blooming Peak

7) Butterfly Photos

8) In the Shop

9) About Our Update List

==========================================

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

==========================================

1) Status of the Population

Each year in mid June we have a decision to make – how many tags should we order this year? The decision is always difficult because by that time we have minimal information on the size and potential growth of the monarch population and don’t know whether the fall migration will be strong or weak. Two years ago we had 300,000 tags manufactured and distributed all of them before the end of the season. Last year we weren’t following the population closely and, being more optimistic than realistic, we ordered up another 300,000 tags. That was a big, expensive mistake. As the summer progressed, we assessed the developing population more carefully and downplayed our expectations for the fall migration with each “Status” report in the monthly Updates. Further, it was clear to many taggers that they had seen few monarchs during the summer. The result was that the tag orders declined and we distributed only about half the 300,000 tags. We’d rather not repeat this experience, so we decided to follow the spring reports more closely. Janis Lentz, who teaches at Weslaco East High School in Weslaco, Texas, has been very helpful in this regard. Janis has carefully assembled the monarch sightings reported to Journey North throughout the spring. These data (Table 1) have been helpful but are also a bit confusing. Ideally, good data yields good patterns and provides insights into the future. Unfortunately, all the population data sets for monarchs to date have not been predictive – the exception being when all indicators are that the population is low – then it is low, at least in the near term. What, if anything, do the numbers in Table 1 tell us about the size of the fall migration and the number of tags to order? As you will see from the analysis below, the signals are mixed and while it is clear that the fall migration this year will be larger than that of last year, it is still too early to declare that the monarch population has recovered. Given that the numbers of observations reported each week has been only slightly better than the low numbers reported in the spring of 2004, we decided to be conservative this year and we have only ordered 200,000 tags. This number sounds like a lot but the tags will be gone in a flash if the monarch population increases substantially in the next two months. So, fair warning – if you want to tag monarchs this fall, order your tags early.

When looking at Table 1, one of the first things that jumps out is the number of sightings for June 2005. This number is considerably higher than for all other June periods. Does this mean that the reproductive success of the first generation, born mostly in Texas, was exceptionally high? Does this mean that the first generation monarchs from Texas arrived late in the northern states and Canada? Do these arrivals in the northern breeding grounds signal the potential for a large fall migration? How this number should be interpreted is not clear. What we can say is that monarchs have been reported from the entire summer breeding range in the United States and from Saskatchewan to Nova Scotia in Canada. The numbers reported are modest but the potential for successful reproduction seems to be good. On the other hand, sightings in June - and the total number of sightings from March through mid June - do not appear to be associated in a consistent manner with population size the following winter. For example, 80 sightings were reported for June of 2004 (the second highest in this six year period) but the resulting overwintering population turned out to be the lowest ever recorded. The low reproduction that followed these relatively high June numbers appeared to be due to cold weather that prevailed in the breeding area from late June through August (see the “Teaching with Monarchs” section in the January Update). Similarly, but conversely, the second and third lowest number of sightings in June (2001 and 2002) were followed by modestly large winter populations. Further, the third highest total (402 in 2000) for the six-year interval was followed by the second lowest overwintering population (2.83 hectares).


Table 1. Number of monarch sightings reported to Journey North from 1 March through 18 June in 2005-2000 exclusive of states west of the Rockies and Florida. In the Totals column the numbers in parentheses are observations in Texas. The second to last column gives the percentage of the total observations that were from Texas and the last column shows the number of hectares of monarchs measured at the overwintering sites the following winter.

* Years with relatively low numbers of butterflies returning from Mexico.
** Two small colonies not included in total.
*** Sometimes erroneously reported as 3.83 hectares.

The three springs with the highest number of monarch sightings in TX (2001-2003) were followed by overwintering populations of average to near average size (7.54 – 11.12 hectares). In years with the lowest number of sightings reported for Texas (2000 and 2004), the overwintering populations were low (2.19 and 2.83 hectares). This pattern in the data supports my long held view that the number of monarchs reaching Texas in March and April, and the conditions (host plants, nectar sources, fire ants, and weather) they encounter, is one of the most important factors that determines the size of the fall migration and the overwintering population.

As I’ve pointed out previously, an analysis of observed sightings such as these rests on the assumption that similar numbers of observers are motivated to report their sightings each year and that weather patterns or other events do not increase or decrease the numbers of observations reported. In this connection it is interesting to note that for the last three years the proportion of the total observations from Texas ranged from 24-26% – a remarkably narrow range. In fact, the outlier in these data, at 11% for 2000, may be due to exceptionally poor spring conditions. The spring of 2000 was extremely dry in Texas and only 43 monarchs were reported that season. Since monarchs appeared early (or on time and in good numbers) in states neighboring Texas that spring, it is possible that monarchs kept moving because of the poor conditions rather than lingering in Texas to reproduce.

==========================================

2) Degree Days Again!

By Chip Taylor and Janis Lentz

Last summer took us by surprise. It was cool and pleasant in eastern Kansas, a welcome change from the typical hot and dry summers that often appear to be precursors of the next dust bowl. However, cool in Kansas translates to even colder further north and last summer proved to be the coldest summer in the main monarch breeding area of the upper Midwest since the volcanic dust cloud from Mt Pinatubo reduced summer temperatures in 1992. In the January Update we explored the impact of the cold temperatures on monarch development. To do so we calculated the total degree days during the summers of 2003 and 2004 for Lawrence, KS and Minneapolis, MN. Monarchs require 720 degree days to complete development from egg to egg, that is, from the time an egg is laid until a female has mated and laid her first egg. At high temperatures these degree days accumulate rapidly and development can be completed in as little as 24 days. At cooler temperatures, degree days accumulate over a longer interval and generation lengths can increase to 40 and even 50 days, thus reducing the potential number of generations per season. Further, an increase in generation length has the effect of exposing the larvae for longer periods to predators, parasites and other environmental hazards that could reduce the proportion of the larvae reaching the adult stage. The formula used to calculate degree days is presented in the “Teaching with Monarchs” article in the January 2005 Update. The formula is quite easy to use. Give it a try.

Since degree day accumulation appears to be one of the ways we can assess the potential development of the monarch population we thought it might be useful to provide the running totals of degree days for a range of cities in the middle of the continent. Each of the data sets starts with the average day of first arrival of monarchs at the latitude of the city. At a later date we will explore the fate of the progeny of monarchs that arrive too early or too late at select latitudes. Data are presented for 2003 (a warm year), 2004 (a cooler year) and 2005.

You can see the impact of cooler temperatures in 2004 in the data for Winnipeg, Canada. If an egg was laid on the 7 of June in each of the three years, the monarch would have completed 19% of its development by the 18th of June (135/720=.19), 11% in 2004, and 16% this year. As you can see for Lawrence, KS, if a monarch laid an egg on the 28th of April, the first egg laying by the next generation would be expected to have occurred (at the earliest) on 18 June for 2003, 10 June for 2004 and 13 June for 2005. If you wish to estimate the fate of eggs laid later, just create a running total starting from that date. Assuming that the temperatures measured at the nearest weather station are representative of your site, a female monarch should begin laying eggs when the total reaches 720.

We will add to the tables below through the September Update.

Winnipeg, Canada:

Minneapolis, MN:

Des Moines, IA:

Lawence, KS:

Dallas, TX: