Tactics and Vectors 98/99
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How to Record Date And Time Of Observations

calander and clock

Record the date and time on the cover sheet of the data sheets just before you start to make observations.  Record the identification number, species and and time for each observation on the data sheets.  It is usually best to record number, species, and time data before recording the rest of the data (altitude, type of flight,   vanishing bearings, etc.).  Be sure to record the time for any additional  measurements and/or observations that you make, particularly if the migration is light.  Record the time that you finish on the cover sheet. 

Two common mistakes to avoid when recording time data are: (1) recording the time as daylight savings time instead of standard time, and (2) failing to record the time for some of the observations.  I avoid the first mistake by not relying on my wristwatch and instead having a separate timepiece set for standard time that is part of the field kit. The second common mistake, failure to record the time for some observations, usually happens when the butterflies are abundant and I get distracted by other migrants before entering the time data for the current observation. The only method I have found to minimize this problem is to practicing good technique and to resist the temptation to work faster just because the butterflies happen to be numerous. Of course, this cautionary note applies to all data entries, not just time data. I hae found that I that can most easily keep pace with the workload when migrating butterflies pass by at the rate of about one every three minutes.

Try to make each observation periods last at least 30 minutes. Maximum time is what ever you can stand. However, a series of one hour observations spread over the 6 - 8 week migration period will provide more complete picture of migratory behavior than eight hours of continuous observations made on a single day, even a day in which the butterflies are passing through in vast numbers. In general, 2 hours per observation period works well. If you go longer, be sure to take a break once an hour, especially during good migration days. Otherwise, your accuracy in record keeping will probably deteriorate and you may even see strange things in the clouds. Try to make observations at different starting times. It has been my experience that most species migrate from morning to at least late afternoon, and monarchs until evening, when ever temperature and wind conditions are favorable.

One rule that I often follow is that when no migrants have been seen for about 30 minutes, and there is no reason to expect conditions to change, it's time to quit, or at least take a break. On the other hand, if there is good reason to believe that migrants will begin flying past shortly, it is a good idea to wait for as long as seems reasonable. Here are several situations in which waiting is often rewarded with interesting data: (1) The sky is clear, and temperatures unfavorable, but increasing steadily. This scenario is often encountered in the morning. When the trigger temperature for migration is reached, anything from one or two migrants to a mass exodus may be observed. (2) Immediately after passage of a cold front when skies are clearing and if temperature and wind direction are favorable, butterflies that waited out the storm may suddenly start migrating, perhaps joining others that appear to have been following the front. (3) As sunset approaches on a day in which there has been abundant thermal activity (lots of fair weather cumulus clouds) and very favorable wind and temperature conditions, butterflies that may have been taking advantage of the excellent soaring conditions and spent most of the day at high altitudes will soon begin descending as thermal activity dies out and to continue migrating for awhile within 10 - 30 m of the ground, using the warm air rising from trees, buildings, etc. If favorable conditions persist thorough the night, see (1). Although each of these approaches work best for studying monarch butterflies, I have had some of them work for other species (e.g. buckeyes, Gulf fritillaries, and pipevine swallowtails).

If you can only afford to make observations one or two times during the migration season don't hesitate to do so because all observations are of equal value. The advantage of the approach of Tactics and Vectors approach is that individual observations gain power by being incorporated to the data base. Over the years, as the data accumulates, a clear picture will emerge of the migratory behavior of the butterflies in each region of the continent. Finally, remember that negative the data is very important for these studies, is essential for hypothesis testing, and should be preserved. Documenting conditions for which migration occurs will provide insight into how the butterflies exploit, or fail to exploit, local weather conditions as they make their way across the continent.