GenevaDear Jerry,
Here is my response to your email. I also saw your recent post to the
listserver "BEE-L" and thought I'd take the opportunity to respond to
both at the same time.
I don't think the weight of the transponders is as serious of an issue
as you indicated. We used transponders that weigh either 3 or 12 mg,
which includes the weight of the bee tags that are used for attaching
them to the bees. We mainly used the 12 mg variety for our study. These
weights are within the range of the weights that the bees carry in
nectar (12-40 mg, 70 mg maximum recorded weight) and pollen (8-30 mg).
Aside from these general considerations, we also published data in the
paper to support the idea that tracked bees showed normal flight.
First, we reported that bees fitted with transponders began their
orientation flights with a brief period of hovering facing the colony
entrance before departure, just as has been previously reported in the
scientific literature. Second, we compared tracked and untracked bees
for hints of a transponder effect and found none. There were no
differences between the duration of the orientation flights of bees
with and without transponders [with: mean ± s.e., 331.6 sec ± 59.2 (n
= 29) vs. without: 340.1 sec ± 26.4 (n = 219), Wilcoxon test, P >
0.05, n.s.].
I can also share with you anecdotal evidence, not formally described in
the paper. We repeatedly saw foraging bees (wearing the transponder)
return to the nest after foraging - they returned to the hive with
pollen on their legs or engorged with nectar. These were not the bees
that were used for analysis of orientation, but we tracked some
foragers just to get a feel for their flight activity. We did present
one track of a successful forager in the paper to illustrate how
different forager flights are than orientation flights.
You're right that the system does have some limitations. We could only
track the movements of one bee at a time. It would be nice to look at
several for the sake of efficiency and to see whether bees that orient
at the same time also fly to the same places. However, the other side
of that coin is that there is no way we could have confused the flight
of one bee with the flight of another bee because there was only one
transponder tracked at a time. Also, Riley's harmonic radar system
does not pick up 'pings' or signals from other kinds of diodes in the
area, as you suggested it might, because of the specificity of the
transponder. Riley has worked very hard on this issue and is quite
confident of the specificity of the transponder, but I'm sorry I am not
liberty to share with you the details. I can tell you first-hand that
the presence of two-way radios at the hive, well within the range of
the radar, created no ambiguities in radar data.
The transponder is too big to allow bees to wear it inside the hive
without altering their behavior. That's why we carefully attached it
and then removed it prior to and after each flight. The transponder-no
transponder comparison mentioned above suggests no ill effects of
transponder application. And since each bee was tracked only once (we
worked only with tagged bees, so we know the identity of each tracked
bee), transponder removal is not an issue. Having to attach and remove
the transponder means that it will be difficult (but not impossible) to
get repeated measures of the same individual, which would really be
nice to go beyond the correlations we report. So we agree that it will
be nice to further miniaturize the transponders, something Joe and his
colleagues are working on.
Finally, you indicated that the harmonic system we used was similar to
that developed to track avalanche victims; this isn't the case. The two
types of harmonic systems are quite different. The harmonic radar
system uses a real scanning radar (which is an acronym for radio
detection/direction and ranging) system that detects both position and
range; the avalanche stuff only provides directional information
(unfortunately for the avalanche victim!)
In summary, while the system is not perfect for every application, we
believe that it did not produce any artifacts in the data we collected.
Best of luck to you with the development of your "RF" system.
Elizabeth Capaldi
Elizabeth A. Capaldi, PhD
Dept of Entomology
505 S. Goodwin Avenue
320 Morrill Hall
University of Illinois at Urbana Champaign
Urbana IL 61801 USA