Printing:
ASSESSING IMPACTS OF RADIOTRANSMITTERS ON
SNAKES WITH A FOCUS ON SURVIVORSHIP
Melanie Horne | Dr. Patrick Gregory | Department of Biology | University of Victoria
Problem
Broadly: Do methods used for monitoring wild
animals impact them in some way?
Specifically: Do radio transmitters attached to/
implanted into snakes cause increased mortality?
Hypothesis
Does usage of radiotelemetry affect survivorship of
snakes?
Background
•
Radiotelemetry is a valuable research tool used to track
wild animals
•
Radiotransmitters are either externally attached or
surgically implanted into snakes, allowing them to be
relocated
•
An assumption of telemetry is that transmitters do not
have any significant effects on the animal carrying them
•
Most researchers use transmitters that make up less than
5% of the body mass of the snake
Project Overview
Methods
Results
•
Snakes in telemetry studies had significantly higher survivorship than
those in natural, free-ranging populations
•
In telemetry studies, there was no significant correlation between
annual survivorship and transmitter length/snake SVL ratio,
transmitter mass/body mass ratio, number of recaptures/week,
post-surgery recovery period or study length
•
Higher survivorship in telemetry studies may be explained by a bias
for adult snakes with inherently higher survivorship, and large margins
of error in estimations of survivorship in free-ranging populations
Results
Next Steps/Future Research
Literature Cited
1.
Briefly summarize known effects of radiotransmitters on all
vertebrates
2.
Compare survivorship of snakes in telemetry studies to
snakes in natural populations (natural mortality rates)
3.
Determine causes of death for snakes carrying
radiotransmitters
4.
Synthesize evidence for effects/no effects of transmitters on
snakes from published literature
1)
Located: 1) studies using radiotelemetry to monitor snakes and 2) studies
estimating natural snake survivorship
•
Extracted information on the species characteristics, sample size, mortality of
snakes, types of transmitters used, surgical conditions, instances of infection, etc
•
Recorded evidence of impacts or no impacts of transmitters on snakes
2) Data analysis and interpretation
•
Compared survival in snakes with and without transmitters for two families of
snakes: Colubridae and Viperidae
•
Examined causes of death for snakes carrying transmitters and looked for
correlations between mortality and surgical conditions, size or weight of
transmitter, etc
Figure 2. Causes of death for snakes in selected radiotelemetry studies. Only studies
where causes of death were stated for all deceased snakes were used.
No effect
Effect
Transmitters did not significantly increase
snake corticosterone (stress) levels (Sperry et
al., 2009)
Transmitters lead to inflammation or infection
in snakes (Lentini et al., 2011; Jackson, 1999
unpublished comm.)
Transmitters usually do not weigh more than
a typical prey item and would not cost extra
energy to carry (Shine and Lambeck, 1985)
Transmitters may cause decreased feeding in
snakes (Lentini et al., 2011),
Most mortality in telemetry studies is due to
“natural” causes (See Figure 2)
Snakes with transmitters exhibit decreased
growth and reproduction (Weatherhead and
Blouin-Demers, 2004)
Table 1. Summary of evidence for effects and no effects of transmitters on snakes from
published literature
•
Future research should focus on other possible impacts of transmitters on
snakes (e.g.: reproduction, movement, growth, etc)
•
A similar analysis could be conducted for a specific species
•
I encourage researchers to report all animal mortalities and health
complications in their telemetry studies
Figure 1. Histograms displaying the spread of annual survivorship values in telemetry studies
and free-ranging populations for snake families Viperidae and Colubridae
Lentini, A.M., Crawshaw, G.J., Licht, L.E., & McLelland, D.J.(2011). Pathologic and hematologic responses to surgically
implanted transmitters in eastern massasauga rattlesnakes (Sistrurus catenus catenus). Journal of Wildlife Diseases, 47, 107-125.
Shine, R. & Lambeck, R. (1985). A radiotelemetric study of movements, thermoregulation and habitat utilization of arafura filesnakes (serpents: acrochordidae). Herpetologica, 41, 351-361.
Sperry, J.H., Butler, L.K., Romero, L.M., & Weatherhead, P.J. (2009). Effects of parasitic infection and radio-transmitters on condition, hematological characteristics and corticosterone concentrations in Texas ratsnakes. Journal of Zoology, 278, 100-107.
Weatherhead, P.J., & Blouin-Demers, J. (2004). Long-term effects of radiotelemetry on black ratsnakes. Wildlife Society Bulletin, 32, 900-906
[0.03, 0.23] [0.23, 0.42] [0.42, 0.61] [0.61, 0.81] [0.81, 1] 0.56, 0.64 0.64,0.73 0.73, 0.82 0.82, 0.91 0.91, 1
Annual Survivorship Annual Survivorship
1.1 1.1 6.2 6.8 7.9 14.1 15.8 19.2 27.7 0 5 10 15 20 25 30 Parasite Starvation Surgical complications Humans Transmitter leakage/exit Hibernation Roadkill Undetermined Predation Percentage of Deaths Cau se of De ath
