Mona Miller wrote:http://www.monarchwatch.org/tagmig/tag.htm
This webpage has more on tagging.
The peak migration date chart from what I can see is a bit out of date. It hasn't seemed to account for changes in weather patterns over the past few years. I used to go by that chart, but couldn't figure out why I was NOT getting significant numbers of butterflies..and each year got worse and worse. Then I heard from people that work with Purple Martins.. the birds migration patterns have shifted over the last several years to account for changes in the weather patterns.... they have been arriving to their breeding grounds earlier and earlier. I think they are now at about 2-3 weeks earlier than what is historically known for them. So going on that information I changed how I hunted monarchs and started earlier than what I normally should expect to begin. Bingo- success. The following year, again, started just a bit earlier than the previous year and got even better success. This year - started at the end of July and finally seemed to have found my new starting point and the actual peak for hunting seems to be the first/second week of August. Migrating wild adults seemed to be peaking about mid- to late-August - not mid- to late- Sept as per the chart. If I were to have continued to use the existing chart to plan when I collect eggs/pillars to raise I would have NO monarchs to tag as they would be long gone and done with. From what I can see from my experience for at least in my area I would say the chart is off by about 3 weeks... very similar to how the purple martins patterns have changed.