By Krista Ruppert, Texas A&M WFSC
‘16
Radiotelemetry
has been an integral part of wildlife research for many years now, but recently
questions regarding increased mortality due to the impact of the extra weight
of these radio transmitters on the survivability of animals, particularly
regarding bobwhites, have been raised. Several studies on the survivability of
bobwhites conducted with attached radio transmitters have concluded that with
the observed survivorship the species should have long been extinct, but
clearly that is not the case. Is it possible that radio transmitters handicap
quail, making them less likely to survive and thus skewing the results of
survivability studies? Despite the research completed on the topic, there have
not been consistent results. Regardless of this, radiotelemetry is a vital tool
for estimating population abundance, survivorship, determining habitat use, and
quail management as a whole.
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A female
bobwhite wearing a bib-style radio transmitter (neck feathers have not been
pulled through neck loop to show transmitter). She also has a leg band, which can
provide information only if she is recaptured, but may cause fewer problems for
the bird than a radio transmitter.
Photo from Texas A&M Wildlife and Fisheries.
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In
1997, Osborne et al. completed a study of captive northern bobwhite in which they
compared the body condition and survival of northern bobwhite with attached backpack-style
radio transmitters, bib-style radio transmitters with neck loops, and quail
with no radio transmitters. They found that birds with radio transmitters had
lower survival and body weight than those without transmitters, with bib-style
transmitters resulting in birds fairing somewhat worse than those with backpack-style
transmitters. Additionally, many of the tagged birds had harness problems,
particularly with the backpack loop, in which they became entangled or needed
repositioning. This is an effect that would likely lead to mortality by
predation in the wild.
Independent of the effects of
radio-transmitters, potential damage to bobwhites during capture, handling, and
restraint also occur, thus reducing survival, as noted by Abbott et al. in
2005. They found that quail frequently overexerted themselves during capture and
handling, an occurrence that could potentially lead to muscle tissue damage,
making them more vulnerable to predation due to a reduced ability to flee. For
more information about bobwhite predation, see the blog post Potential
Predators Associated with Northern Bobwhite Nesting. Abbott et al. (2005)
also found that a treatment with vitamin E and selenium (a well-accepted
treatment for avian muscle damage) greatly improved survival of captured and
radio-tagged bobwhites. Perhaps the most well-known study regarding bobwhite
and radio-handicapping, however, is by Guthery and Lusk in 2004. After
analyzing a large variety of modeling reports on quail survivability, they
found that only 17% of studies on bobwhite survival revealed survival rates that
could reasonably sustain the populations. By their calculations, most of the
data seemed to suggest bobwhites should have gone extinct long ago, as they
simply did not appear to have survival rates sufficient to maintain their
populations. They determined the observed low survival rates were probably due
to radio-handicapping of the tagged quail.
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Some example
radio-transmitters used on northern bobwhite. These are comparable in size to a
penny and typically weigh about 6 grams.
Photo from Texas A&M AgriLife Today. |
A study by Folk et al. in 2007 in response to Guthery and Lusk (2004) identified potential biases in their study, calling for more empirical research to be completed on the subject rather than relying on the imprecise samples of the past. Hernandez et al. in 2007 attempted to replicate the study of Osborne et al. (1997) by evaluating the effects of radio-transmitters on captive bobwhites, but they found no change in the body size or energy expenditure between quail wearing necklace-style tags and quail without tags. However, because it was a captive study, the potential effects on locomotion, foraging, and thermoregulation were not evaluated. Studies with wild bobwhites have also been completed and are considered more relevant to wildlife management than those of captive birds. A study by Palmer and Wellendorf in 2007 compared survival rates between necklace-style radio-tagged and banded bobwhites over 5 years, finding no difference in mortality between the two. A similar study by Terhune et al. in 2007 yielded similar results regarding necklace-style transmitters measured over an 8 year period, but recommended taking care to reduce stress during trapping and handling.
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A female
bobwhite wearing a radio-transmitter. Note the antennae extending behind her.
Photo from Texas A&M AgriLife Today. |
With so
many conflicting results, how is it possible to know whether radio-handicapping
is something to be concerned about? As stated before, there is not a definitive
answer. The effects of radio-transmitters on northern bobwhite have yet to be
fully determined and further studies will be necessary to truly determine the
potential of radio-handicapping quail. In the meantime, it is important to take
bobwhite survivability calculations based on radiotelemetry data with a grain
of salt, keeping in mind that a bias could be present.
Call counts, discussed in the blog
post Calling
All Quail, can be used to estimate norther bobwhite population abundance,
but variability within this method makes precise estimates difficult. Banding
can provide estimates, but the process of catching and banding birds can also
lead to lower survival, and information can only be obtained if the bird is
recaptured. As for what can be done to improve the reliability of radiotelemetry
data, it is important to reduce stress of the quail while capturing and tagging
them. Minimal handling time and reduced exertion during restraint can help
greatly, and treatments of vitamin E and selenium (at a cost of less than $0.01
per bird) could be useful for treating muscle damage occurring during
restraint. Additionally, the use of necklace-style transmitters appears to be
the ideal choice for reducing entanglement and potential predation due to
restricted movement. Though there is not a clear answer regarding the effects
of radio transmitters on northern bobwhites, they are still a useful tool and
the strategies detailed above can be used to optimize their efficiency to
acquire valuable data.
Literature Cited
Abbott, C. W., C.
B. Dabbert, D. R. Lucia, and R. B. Mitchell. 2005. “Does muscular damage during
capture and handling handicap radiomarked northern bobwhites?” Journal of Wildlife Management
69(2):664-670.
Folk, T. H., J.
B. Grand, W. E. Palmer, J. P. Carroll, T. M. Terhune, S. D. Wellendorf, and H.
L. Stribling. 2007. “Estimates of survival from radiotelemetry: a response to
Guthery and Lusk.” Journal of Wildlife
Management 71(4):1027-1033.
Guthery, F. S.
and J. J. Lusk. 2004. “Radiotelemetry studies: are we radio-handicapping
northern bobwhites?” Wildlife Society
Bulletin 32(1):194-201.
Hernández, F., J.
A. Arredondo, F. Hernandez, D. G. Hewitt, S. J. DeMaso, and R. L. Bingham.
2004. “Effects of radiotransmitters on body mass, feed consumption, and energy
expenditure of northern bobwhites.”
Wildlife Society Bulletin 32(2):394-400.
Osborne, D. A.,
B. J. Frawley, and H. P. Weeks. 1997. "Effects of radio tags on captive
northern bobwhite (Colinus virginianus)
Body Composition and Survival." American Midland Naturalist
137(2):213.
Palmer, W. E. and
S. D. Wellendorf. 2007. “Effect of radiotransmitters on northern bobwhite
annual survival.” Journal of Wildlife
Management 71(4):1281-1287.
Terhune, T. M.,
D. C. Sisson, J. B. Grand, and H. L. Stribling. 2007. “Factors influencing
survival of radiotagged and banded northern bobwhites in Georgia.” Journal of Wildlife Management 71(4):1288-1297.