The effect of research activities and winter precipitation on voiding behaviour of Agassiz’s desert tortoises (Gopherus agassizii)
Mickey Agha A , Mason O. Murphy B , Jeffrey E. Lovich C , Joshua R. Ennen D , Christian R. Oldham A , Kathie Meyer E , Curtis Bjurlin F , Meaghan Austin C , Sheila Madrak G , Caleb Loughran H , Laura Tennant C and Steven J. Price A I
+ Author Affiliations
- Author Affiliations
A Department of Forestry, University of Kentucky, Lexington, KY 40546-0073, USA.
B Department of Biology, University of Kentucky, Lexington, KY 40546-0225, USA.
C US Geological Survey, Southwest Biological Science Center, MS-9394, Flagstaff, AZ 86001, USA.
D Tennessee Aquarium Conservation Institute, 201 Chestnut St, Chattanooga, TN 37402, USA.
E 19233 Stratford Way, Apple Valley, CA 92308, USA.
F Stantec Consulting, 2617 Chamberlain Avenue, Madison, WI 53705, USA.
G Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4614, USA.
H Central Washington University, Department of Biological Sciences, Ellensburg, WA 98926, USA.
I Corresponding author. Email: steven.price@uky.edu
Wildlife Research 41(8) 641-649 https://doi.org/10.1071/WR14196
Submitted: 26 June 2014 Accepted: 27 January 2015 Published: 14 April 2015
Abstract
Context: There is little information available on how research activities might cause stress responses in wildlife, especially responses of threatened species such as the desert tortoise (Gopherus agassizii).
Aims: The present study aims to detect behavioural effects of researcher handling and winter precipitation on a natural population of desert tortoises in the desert of Southwestern United States, over the period 1997 to 2014, through extensive assessments of capture events during multiple research studies, and capture–mark–recapture survivorship analysis.
Methods: Juvenile and adult desert tortoises were repeatedly handled with consistent methodology across 18 years during 10 study seasons. Using a generalised linear mixed-effects model, we assessed the effects of both research manipulation and abiotic conditions on probability of voiding. Additionally, we used a Cormack–Jolly–Seber model to assess the effects of winter precipitation and voiding on long-term apparent survivorship.
Key results: Of 1008 total capture events, voiding was recorded on 83 (8.2%) occasions in 42 different individuals. Our top models indicated that increases in handling time led to significantly higher probabilities of voiding for juveniles, females and males. Similarly, increases in precipitation resulted in significantly higher probabilities of voiding for juveniles and females, but not for males. Tortoise capture frequency was negatively correlated with voiding occurrence. Cormack–Jolly–Seber models demonstrated a weak effect of winter precipitation on survivorship, but a negligible effect for both voiding behaviour and sex.
Conclusions: Handling-induced voiding by desert tortoises may occur during common research activities and years of above average winter precipitation. Increased likelihood of voiding in individuals with relatively low numbers of recaptures suggested that tortoises may have perceived researchers initially as predators, and therefore voided as a defensive strategy. Voiding does not appear to impact long-term survivorship in desert tortoises at this site.
Implications: This study has demonstrated that common handling practices on desert tortoise may cause voiding behaviour. These results suggest that in order to minimise undesirable behavioural responses in studied desert tortoise populations, defined procedures or protocols must be followed by the investigators to reduce contact period to the extent feasible.
Additional keywords: conservation, research manipulation, Sonoran Desert, survival, wildlife handling.
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