How to Record Date And Time Of Observations
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.