Some terrestrial chelonians, including Mohave desert tortoises Gopherus agassizii, reabsorb water from urine stored in their bladders, and thus they may experience an elevated risk of dehydration if they urinate in response to interactions with humans. Field biologists can use several methods to attempt to replace voided urine with hydrating fluids, but each has drawbacks or unknown efficacy. Here we evaluate the efficacy of offering juvenile Mohave desert tortoises water via needle-free syringe for ingestion through the nasal and oral passages. Only tortoises offered ≥ 12 mL of water, which equated to ≥ 40 mL of water/kg body weight, gained weight during the hydration attempt. We recommend that field biologists offer at least 40 mL of water/kg body weight when using the nasal–oral hydration method with a minimum of 15 mL offered regardless of body weight. The nasal–oral technique and minimum volume recommendations may be useful for other terrestrial chelonians, and we recommend attempting rehydration via this simple technique when alternate methods are not available to alleviate the potentially harmful effects of handling-induced loss of urine.

Field biologists can inadvertently harm wildlife during field studies through physical injuries or induction of stress responses. The Mohave desert tortoise Gopherus agassizii, a threatened species pursuant to the U.S. Endangered Species Act (ESA 1973, as amended; USFWS 1990) that inhabits the southwestern United States, may urinate during interactions with humans. Mohave desert tortoises are among the terrestrial chelonians that have large urinary bladders from which they reabsorb water from urine to regulate plasma osmolality and avoid or delay onset of dehydration (Dantzler and Schmidt-Nielson 1966; Minnich 1977; Nagy and Medica 1986; Peterson 1996). Because Mohave desert tortoises live in arid environments with infrequent opportunities to drink and replenish their bladders with dilute urine, inadvertently causing an individual to urinate can be detrimental and likely increases mortality risk as seen in the closely related Sonoran desert tortoise Gopherus morafkai (Averill-Murray 2002). Juvenile Mohave desert tortoises have the highest risk of voiding, followed by adult females, then adult males (Agha et al. 2015). Juvenile tortoises are highly vulnerable to dehydration when stored urine is voided, as their natural rate of water loss is greater than that of adults when expressed as percentage of body mass. Without initiating conservative behaviors or having environmental features available to help lessen natural water loss, juvenile Mohave desert tortoises can lethally dehydrate in less than 2 mo (Wilson et al. 2001).

Field biologists can strive to lessen the effects of handling-induced loss of urine by tortoises through attempts to replenish fluids. In order to handle Mohave desert tortoises, field biologists need to obtain permission from the U.S. Fish and Wildlife Service (USFWS) and the relevant state wildlife agencies. The agencies issue permits that contain procedures to follow and require permit holders to collect and submit data about size, health, and behavior of the animals that may be ancillary to the primary experiment or monitoring being conducted. The USFWS has approved three procedures for attempting to rehydrate Mohave desert tortoises that void bladder contents: injections of sterile saline into the epicoelomic region between the coelomic cavity's membrane and the shell (McArthur 2004; USFWS 2016), soaks in shallow baths of water (McArthur 2004; USFWS 2016), and offers of water via needle-free syringe for uptake through nasal and oral passages (USFWS 2016). Depending on individuals' qualifications, some or all of these procedures are included in the issued permits.

An advantage of epicoelomic fluid injection is the placement of a known volume of saline directly into the tortoise for absorption. The volume recommended for Mohave desert tortoises is 20 mL/kg body weight up to a maximum of 60 mL (USFWS 2016). This technique is not recommended for Mohave desert tortoises < 150 mm in straight midline carapace length (USFWS 2016), which excludes most juveniles as the species reaches sexual maturity at straight midline carapace lengths of approximately 180 mm. Additionally, field biologists need to be trained in proper administration to minimize risks of infection and organ damage.

More natural ingestion of water via drinking and cloacal absorption can occur when biologists soak tortoises in shallow baths of water. A previously published analysis showed that adult Mohave desert tortoises are capable of a weight gain (mean ± SD) of 13.2 ± 9.1% after a water bath, but may not gain weight if already well hydrated when offered the water (Field et al. 2007). Wilson et al. (2001) found that all 24 juveniles collected from an outdoor enclosure drank and gained weight when soaked in water baths. The value of water baths for juvenile Mohave desert tortoises in a wild setting still needs evaluation, but it is possible that tortoises could ingest significant volumes of water. Disadvantages of this method include the need for field biologists to carry bath containers that can be disinfected between individuals and large volumes of water.

Nasal–oral fluid administration is a simple technique that involves gently dripping or spraying water out of a needle-free syringe that is held close to the tortoise's nares or mouth (Figure 1). Biologists do not inject water into the nares or mouth by force but rather the tortoise must actively accept and ingest the water (USFWS 2016). Although not specified in the instructions for Mohave desert tortoises (USFWS 2016), it has been common practice to cease offering water if the tortoise shows no interest and to continue offering water while the tortoise appears to be ingesting it, regardless of how much water has been offered. Despite being implemented in the field, the efficacy of the nasal–oral technique for introducing a meaningful amount of water into a Mohave desert tortoise was unknown. Our objective was to investigate the usefulness of this method and evaluate the existing recommendation of offering 20 mL water/kg body weight (i.e., the standard fluid replacement volume used by veterinarians experienced in working with reptiles).

Figure 1.

Author (K.J.F.) demonstrates the overhead orientation of offering water via needle-free syringe (nasal–oral fluid administration) to an adult Mohave desert tortoise Gopherus agassizii at the Desert Tortoise Conservation Center in Las Vegas, Nevada, during a training session in April of 2014. The tortoise remains unrestrained and must actively accept water through the oral and nasal passages. Photo by Terry E. Christopher.

Figure 1.

Author (K.J.F.) demonstrates the overhead orientation of offering water via needle-free syringe (nasal–oral fluid administration) to an adult Mohave desert tortoise Gopherus agassizii at the Desert Tortoise Conservation Center in Las Vegas, Nevada, during a training session in April of 2014. The tortoise remains unrestrained and must actively accept water through the oral and nasal passages. Photo by Terry E. Christopher.

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For field projects that involve the translocation of Mohave desert tortoises, the USFWS requires field biologists to conduct assessments of the individuals' health using protocols described in their most recent health assessment handbook (USFWS 2016). During these assessments, field biologists handle tortoises for up to 30 min and often collect biological samples. Despite the use of proper handling techniques, some tortoises void a portion of their bladder contents. When this happens, field biologists attempt to rehydrate tortoises using epicoelomic injection, water bath, or nasal–oral fluid administration. They present hydrating fluids regardless of the volume voided. Prior to 2016, the USFWS required permit holders to record and submit data on initial weight, postvoid weight, and posthydration weight. The type and accuracy of scales to be used was not specified. Access to these data allowed us to assess the efficacy of nasal–oral fluid administration through changes in body mass.

We reviewed data collected from May 2011 through September 2014 at sites associated with the translocation of wild Mohave desert tortoises in southern California for occurrences of tortoises < 600 g that voided any portion of bladder contents during health assessments and subsequently were offered water via the nasal–oral method. We found 20 occurrences that included complete data for body weights and volumes of water offered (Table S1, Supplemental Material). These 20 occurrences involved 18 individual tortoises; two individuals (tortoise no. 354 and no. 633) had occurrences in 2013 and 2014. The tortoises ranged in weight from 99 to 475 g and in straight midline carapace length from 77 to 127 mm. Biologists had offered the tortoises 2–45 ml of water or 10–164 mL/kg of body weight. We restricted our analysis to juveniles with initial weights of < 600 g because field biologists predominately used spring scales, which rendered changes in mass less detectable for large size-classes of tortoises that were weighed using scales with divisions as large as 50 g. Biologists used 100-g (1-g divisions, precision ± 0.3%) or 600-g (5-g divisions, precision ± 0.3%) Pesola spring scales (Pesola Präzisionswaagen AG, Schindellegi, Switzerland) to weigh small tortoises and interpolated to the nearest gram. We were more likely to detect the potentially small amounts of water ingested via the nasal–oral method due to the readability of the scales used for tortoises of this size than would have been possible for larger tortoises. Additionally, we were specifically interested in this size class because the minimum body size for hydration of Mohave desert tortoises via epicoelomic injection was increased from 100 to 150 mm straight midline carapace length in 2016 (USFWS 2016), making understanding the efficacy of nasal–oral administration a priority in order to minimize dehydration risks to juveniles. This was the only revision to the hydration protocols that the USFWS made since 2011, so we reference their 2016 health assessment protocols (USFWS 2016) throughout this paper for clarity.

We conducted analyses using Real Statistics 5.4.2 (Zaiontz 2018). After checking data normality with a Shapiro–Wilk test, we used simple linear regression to compare changes in body weights after hydration (expressed as percentage of postvoid weight) with amounts of water offered.

Although most records in the large data set that we reviewed did not qualify for our analysis (e.g., incomplete body weight and water volume data, nasal–oral not chosen as rehydration method), we found that juvenile tortoises up to 500 g in body weight voided some portion of bladder contents in 24% of health assessment–related handling events (N = 968), whereas adults (i.e., ≥ 180 mm in straight midline carapace length) voided in 6% of health assessment–related handling events (N = 2,086). Of the voiding occurrences that qualified for our analyses, juvenile tortoises had detectable weight loss, up to 6% of body weight, in 15 of the 20 occurrences (Table 1; Table S1, Supplemental Material). In 40% (6/15) of these occurrences of weight loss, tortoises gained weight following nasal–oral administration of fluids (Table 1; Table S1, Supplemental Material). No tortoises gained detectable weight during hydration attempts that had not lost detectable weight after voiding (Table S1, Supplemental Material). Additionally, none of the tortoises offered ≤ 10 mL of water gained weight (Figure 2), regardless of whether or not volume offered was several times the recommended amount of 20 mL/kg (Table 1). The tortoises offered > 10 mL of water did not increase in weight linearly as the amount of water offered increased (actual no. of milliliters offered: R2 = 0.02, F1,8 = 0.14, P = 0.72; mL/kg offered: R2 = 0.11, F1,8 = 0.86, P = 0.38) even when only considering those that had initial detectable weight loss (actual no. of milliliters offered: R2 < 0.01, F1,6 < 0.01, P = 0.99; mL/kg offered: R2 = 0.54, F1,6 = 5.86, P = 0.06). When evaluating the possibility of increasing the recommended hydration volume, we found that tortoises offered less than 40 mL/kg did not gain weight while some of the tortoises offered equal to or more than that volume did gain weight (Figure 3). One tortoise regained all of the weight it had lost and ended a few grams heavier than its initial weight (Table S1, Supplemental Material).

Table 1.

Changes in body weight of wild juvenile Mohave desert tortoises Gopherus agassizii from southern California from 2011 through 2014 after observation of handling induced voiding of urine and subsequent changes in body weight after rehydration was attempted by field biologists using the nasal–oral fluid administration technique. Sizes of tortoises (straight midline carapace length) and volumes of water offered are also shown.

Changes in body weight of wild juvenile Mohave desert tortoises Gopherus agassizii from southern California from 2011 through 2014 after observation of handling induced voiding of urine and subsequent changes in body weight after rehydration was attempted by field biologists using the nasal–oral fluid administration technique. Sizes of tortoises (straight midline carapace length) and volumes of water offered are also shown.
Changes in body weight of wild juvenile Mohave desert tortoises Gopherus agassizii from southern California from 2011 through 2014 after observation of handling induced voiding of urine and subsequent changes in body weight after rehydration was attempted by field biologists using the nasal–oral fluid administration technique. Sizes of tortoises (straight midline carapace length) and volumes of water offered are also shown.
Figure 2.

Percentages of body weight regained by wild juvenile Mohave desert tortoises Gopherus agassizii in southern California in relation to actual number of milliliters of water offered via the nasal–oral fluid administration technique in attempt to alleviate the effects of stored urine lost during handling that occurred in 2011 through 2014.

Figure 2.

Percentages of body weight regained by wild juvenile Mohave desert tortoises Gopherus agassizii in southern California in relation to actual number of milliliters of water offered via the nasal–oral fluid administration technique in attempt to alleviate the effects of stored urine lost during handling that occurred in 2011 through 2014.

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Figure 3.

Percentages of body weight regained by wild juvenile Mohave desert tortoises Gopherus agassizii in southern California in relation to the mL/kg of body weight of water offered via the nasal–oral fluid administration technique in attempt to alleviate the effects of stored urine lost during handling that occurred in 2011 through 2014. Open circles identify those tortoises that voided small unmeasurable amounts prior to the rehydration attempt.

Figure 3.

Percentages of body weight regained by wild juvenile Mohave desert tortoises Gopherus agassizii in southern California in relation to the mL/kg of body weight of water offered via the nasal–oral fluid administration technique in attempt to alleviate the effects of stored urine lost during handling that occurred in 2011 through 2014. Open circles identify those tortoises that voided small unmeasurable amounts prior to the rehydration attempt.

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We found that juvenile Mohave desert tortoises are able to ingest water that is offered via the nasal–oral hydration method. While the volumes ingested by tortoises in our study were small and most tortoises did not regain the full amounts of body weight lost during voiding, we propose that the technique is beneficial in situations where other methods of rehydration are unavailable. Urine lost by tortoises is heavier than equivalent volumes of fresh water, thus we do not expect that tortoises need to regain amounts of body mass equivalent to that lost to alleviate the effects of handling-induced voiding. We interpret with caution the fact that none of the tortoises offered ≤ 10 mL gained weight, yet err in being liberal with water when making recommendations on volumes to offer. Biologists were not required to record the behaviors of tortoises during rehydration attempts. If tortoises showed no interest in ingesting water, biologists may have offered ≤ 10 mL. Regardless, the recommendation to offer 20 mL/kg in total (USFWS 2016) would have resulted in all tortoises being offered 9.5 mL or less, thus reducing the potential benefit of attempted rehydration.

Interestingly, the tortoises that had no detectable change in weight after voiding did not gain any weight after rehydration was attempted. Because biologists attempted rehydration regardless of volume voided (including a few drops of urine), the tortoises may have recognized that their hydration states had not been compromised and had no interest in ingesting the offered water—a similar behavior to well-hydrated tortoises in a previous study (Field et al. 2007). It is also possible that tortoises did ingest some water, but voided during the rehydration attempt. Mohave desert tortoises tend to void bladder contents during or after drinking water (Medica et al. 1980). Thus, we may not have detected positive changes in weight; however, tortoises may have ingested fresh water and affected their hydration status. Another possibility is that biologists caused additional stress by attempting to rehydrate individuals that had no need to be rehydrated. For example, one tortoise in the present study lost 3 g between the postvoid and posthydration weight measurements (Table S1, Supplemental Material), indicating that additional voiding occurred, yet we could not confirm intake of water.

Mohave desert tortoises have increased incidence of voiding as handling time increases (Agha et al. 2015). In the data set that we examined, juveniles voided in 24% of health assessment–related handling events, which is nearly twice the risk predicted by Agha et al. (2015) for a 30-min handling event. We suspect that void risk is affected by type of handling in addition to duration. During health assessments of the Mohave desert tortoise, biologists frequently collect biological samples (e.g., blood via venipuncture and swabs of the oral cavity), which is more invasive than the handling involved to weigh, measure, mark, and attach data loggers or tracking devices. Although mortality rates of juveniles in relation to voiding occurrence remain unknown, any increase in water loss through interaction with humans is undesirable and likely detrimental given their rates of natural water loss, unless fresh drinking water is available shortly thereafter. Because the USFWS's health assessment protocols for the Mohave desert tortoise (USFWS 2016) limit interaction time to 30 min (not including hydration attempts after the assessment) and require attempts to rehydrate after voiding, we do not recommend changes to the maximum interaction time.

We recommend an increase in the volume of fluids to be offered via the nasal–oral technique from 20 mL/kg to a minimum of 40 mL/kg with an absolute minimum of 15 mL regardless of the Mohave desert tortoise's size. This would result in biologists offering a minimum of 15 mL of water to all tortoises ≤ 375 g and a minimum of 40 mL/kg for all tortoises > 375 g, which always computes to more than 15 mL. If water is accepted by the tortoise, there is little risk in continuing to offer water until the tortoise loses interest. Biologists do not risk introducing too much water into the tortoise when using this method, as the tortoise is unrestrained and must actively intake the water. Additionally, most of the water offered is not ingested and runs down the tortoise's face to the ground (Table 1). We recommend further evaluation with larger sample sizes to determine if attempting to rehydrate tortoises that void very small amounts (i.e., droplets) could be more detrimental than beneficial by causing additional stress to animals that are not in need of rehydration and potentially inducing additional voiding. If a tortoise shows strong aversion to the water being offered, we recommend ceasing the hydration attempt. Evaluation of the technique for larger tortoises is needed, but until that time we recommend adopting the 40-mL/kg minimum, if lack of equipment or trained personnel does not allow for administration of epicoelomic injections or water baths.

Mohave desert tortoises are not unique among terrestrial chelonians in their voiding of urine in response to handling (Hernandez-Divers 2005; Ernst and Lovich 2009), nor in their ability to retain urine in reservoir-type bladders for use in osmoregulation. Multiple species of tortoises, including the closely related Sonoran desert tortoise, benefit from field biologists being prepared to rehydrate individuals that void in response to interaction with humans. While use of the nasal–oral fluid administration method is uncommonly reported, there is evidence that species in addition to the two desert tortoises may be receptive to water offered in this manner. Wild-caught spider tortoises Pyxis arachnoides in a temporary captive environment exhibited specific postures when offered drops of water from a pipette overhead and were observed to intake water through their nares and mouth (Currylow 2012). For any species of tortoise, we recommend epicoelomic injection as the first choice among rehydration methods when the tortoises are large enough and properly trained personnel are available. Our next choice is a soak in a water bath, which is applicable to any size of terrestrial chelonian, when appropriate bath containers and volumes of water are available. We suggest that nasal–oral fluid administration with our minimum volume recommendations is worthwhile as a last-resort effort to rehydrate terrestrial chelonians and recommend that field biologists attempt rehydration via this simple method when other options are not available to alleviate the potentially harmful effects of voided urine.

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental materials. Queries should be directed to the corresponding author for the article.

Table S1. Body size and weight measurements of wild juvenile Mohave desert tortoises Gopherus agassizii in southern California that voided urine when handled by field biologists for assessments of their health during 2011 through 2014. Also included are volumes of water offered via the nasal–oral fluid administration technique and calculations of changes in body weight expressed both in grams and percentage of change.

Found at DOI: https://doi.org/10.3996//042017-JFWM-034.S1 (13 KB XLSX).

Reference S1. [USFWS] U.S. Fish and Wildlife Service. 2016. Health assessment procedures for the Mohave desert tortoise Gopherus agassizii: a handbook pertinent to translocation. Desert Tortoise Recovery Office, U.S. Fish and Wildlife Service, Reno, Nevada.

Found at DOI: https://doi.org/10.3996/042017-JFWM-034.S2 (2.58 MB PDF); also available at https://www.fws.gov/Nevada/desert_tortoise/documents/reports/2016/may-2016-desert-tortoise-health-eval-handbook.pdf.

P. Woodman provided a video of the nasal-oral hydration technique being implemented in the field that convinced us that tortoises could be receptive to water offered in this manner. L. Backus, W. Ball, A. Currylow, S. DiRuzzo, C. Furman, M. Havelka, K. Herbinson, C. Himmelwright, T.G. Jackson, G. Keyes, S. Lindey, C. Llewellyn, R. McGuire, J. Meyers, L. Pavliscak, B. Reiley, A. Scheib, J. Smith, N. Stephens, J. Valentine, and B. Weise collected the data on the juveniles used in the analyses. C. Grouios and the WildFauna Inc. team proofed data and assisted with data queries. A. Fesnock, A. Scheib, and D. Davis assisted with acquiring the proofed data set. Field data were collected under the USFWS's Biological Opinion for BrightSource Energy's Ivanpah Solar Electric Generating System Project (8-8-10-F-24) and funded by NRG Energy Services, Google Inc., and BrightSource Energy through three limited liability companies: Solar Partners I, Solar Partners II, and Solar Partners VIII. Two anonymous reviewers, the Associate Editor, and L. Allison provided comments and suggestions that improved this manuscript. R. Averill-Murray supported our efforts to investigate the dataset.

Any use of trade names of specific products is for descriptive purposes only and does not imply endorsement of the U.S. Government. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service, Arizona Exotic Animal Hospital, or San Diego Zoo Global.

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Author notes

Citation: Field KJ, Johnson JD, Lamberski N. 2018. Nasal–oral water administration for rehydration of juvenile Mohave desert tortoises. Journal of Fish and Wildlife Management 9(2):591–597; e1944-687X. doi:10.3996/042017-JFWM-034

Supplemental Material