Effects of Marking Uta stansburiana (Sauria: Phrynosomatidae) with Xylene-based Paint.

James L. Boone
Nevada State Museum, 700 Twin Lakes Drive, Las Vegas, NV 89107

Elizabeth A. LaRue
Nevada State Museum, 700 Twin Lakes Drive, Las Vegas, NV 89107

Population biologists often rely on marks to identify individual animals (Nietfeld et al. 1994). For many years, herpetologists have marked reptiles with toe-clips, scale-clips, and paint (Ferner 1979), and although any marks potentially affect animals, these generally have been shown not to affect survival or other biological processes (e.g., Brown and Parker 1976; Jones and Ferguson 1980; Weatherhead et al. 1995). As technologies change, new methods of marking appear. Some new methods obviously require testing before one can be sure that the method does not adversely affect the target animal (e.g., glass beads, Fisher and Muth 1989; radioactive tags, Pendleton 1956; PIT tags, Prior and Weatherhead 1996).

One example of a new method entering use without being tested was a modification of standard painting techniques. Herpetologists have long used model paint (e.g., Testor Corporation paints) to mark lizards and snakes without adverse effects (e.g., Jones and Ferguson 1980). However, using model paint in the field can be messy and may require researchers to carry and use paint thinner, leading one to look for more convenient methods. Some researchers have used fingernail polish, while others have found quick-drying Faber-Castel(tm) paint-pens more convenient for marking reptiles than either model paint or fingernail polish. The carrier in these paint-pens, however, is xylene, and xylene has well-known toxic affects on animals (d'Azevedo et al. 1996; Rana and Kumar 1997). One might assume that marking a reptile with a small amount of paint would result in a negligible dose of xylene, especially in hot, arid environments where the paint dries almost immediately. Based on this assumption, one might conclude that using paint-pens would not affect lizard behavior, survival, or other demographic parameters. However, no one has tested this assumption.

We conducted a pilot study to test the null hypothesis that xylene-based paint-pens have no adverse affect on the survival of side-blotched lizards (Uta stansburiana), a small insectivorous lizard that is common in the western U.S.A. and northern Mexico. We captured 35 Uta (18 female; 17 male; 19 adults, snout-vent length, SVL > 39 mm; 16 juveniles, SVL < 39 mm) from five locations around southern Nevada (October, 1996 through October, 1997). We held the lizards in a lab and housed them on sand and gravel in individual 2-liter jars. We exposed the lizards to ambient light and provided full-spectrum lamps for heat during daylight hours. Daily ambient temperatures in the lab ranged from about 13-27C. Before marking the lizards, we kept them in captivity for 2-3 days to ensure that no animals died immediately after capture.

We painted 21 lizards and used 14 as unpainted controls. We painted lizards in a manner similar to how Uta had been marked during a mark-recapture study (Boone et al. 1998). We placed a spot of paint on the dorsum (diameter < 1 cm, less than the width of the dorsal surface) generally every 3-4 days until each lizard had been painted four times. This simulated four capture-recapture events over two weeks using a day-specific color of paint on each day of sampling. In the field, large spots (i.e., the width of the dorsum) were used so that the paint color could be seen from a distance, presumably reducing stress on the lizards by limiting the number of times that observers had to closely approach the animals during exhaustive searches of 1-ha plots on each day of sampling. Each successive spot of paint was placed on top of the previous spots. We recorded mortality and sleeping behavior (i.e., spending the night above or below ground) for two weeks.

Of the 21 painted lizards, 5 died (4 juveniles, 1 adult; 24%), all of which had been painted at least twice. No unpainted lizards died. While the sample size was small, the result was statistically significant (Gadj = 5.408, P = 0.02). Sleeping behavior also changed. When first brought into the lab, all lizards burrowed into the substrate and spent every night underground. During the remainder of the study, most unmarked lizards continued to burrow underground almost every night (TABLE 1). By contrast, 8 of 11 (73%; P = 0.06) painted juveniles, and 2 of 10 painted adults (20%; P = 0.62), switched sleeping location and spent almost every night aboveground (TABLE 1).

When first applied, the paint sometimes appeared to irritate the lizards: they sometimes gaped, some exhibited dorso-ventral flattening as if a weight had been placed on their back, and a few flexed their bodies 45-60 degrees backwards lifting their front legs off the ground or pressing their front legs against the side of their jar. Some of the painted lizards became lethargic. There seemed to be a dose-response relationship. More smaller lizards than larger lizards showed negative responses to the paint, and the lizards that showed a negative response often did so after their second paint treatment.

Not all samples gave the same result. A group of five lizards (SVL = 42-47 mm) captured south of Las Vegas never exhibited any negative reactions (3 marked, 2 unmarked). In contrast, from a group of nine lizards caught west of Las Vegas, four (SVL = 37-45 mm) of five painted lizards exhibited negative reactions, and the lizard that didn't show a response (SVL = 52 mm) was the largest of these five.

The xylene-based paint used in this study was associated with the death of some lizards; it was also associated with altered behavior in others that could affect survival. If lizards in the field failed to seek cover at night, they may be subjected to increased predation or stressed by exposure to low temperatures at night.

The results of this pilot study suggest that Uta stansburiana experiences a dose-related, adverse effect from this marking technique. While small amounts of paint may not affect these lizards, it appears that xylene-based paints can introduce unnecessary bias into field experiments, and therefore field biologists should avoid using these paints for marking lizards or other animals. An important point is to beware of new methods in the guise of old ones, and to carefully examine new techniques and procedures before assuming they are the same as the old favorites.

Acknowledgments.-We thank D. Beck, J. Freilich, A. Heindl, and G. Austin for helpful comments on the manuscript.

LITERATURE CITED

BOONE, J. L., C. L. SOWELL, M. COX, AND R. A. GREEN. 1998. Species composition and abundance of reptile populations at Yucca Mountain, NV, with Annotated Checklist. U.S. Department of Energy, Civilian Radioactive Waste Management System, Management & Operating Contractor, Report B00000-01717-5705-00038.

BROWN, W. S., AND W. S. PARKER. 1976. A ventral scale clipping system for permanently marking snakes (Reptilia, Serpentes). J. Herpetol. 10:247-249.

d'AZEVEDO, P. A., M. TANNHAUSER, S. L. TANNHAUSER, AND H. M. T. BARROS. 1996. Hematological alterations in rats from xylene and benzene. Vet. Human Toxicol. 38:340-344.

FERNER, J. W. 1979. A review of marking techniques for amphibians and reptiles. Soc. Study Amph. Rept., Circular 9:1-42.

FISHER, M., AND A. MUTH. 1989. A technique for permanently marking lizards. Herpetol. Rev. 20:45-46.

JONES, S. M., AND G. W. FERGUSON. 1980. The effect of paint marking on mortality in a Texas population of Sceloporus undulatus. Copeia 1980:850-854.

NIETFELD, M. T., M. W. BARRETT, AND N. SILVY. 1994. Wildlife marking techniques. In T. A. Bookhout (ed.), Research and Management Techniques for Wildlife and Habitats, pp. 140-168. Allen Press, Lawrence, Kansas.

PENDLETON, R. C. 1956. Uses of marking animals in ecological studies: labeling animals with radioisotopes. Ecology 37:687-689.

PRIOR, K. A., AND P. J. WEATHERHEAD. 1996. Habitat features of black rat snake hibernacula in Ontario. J. Herpetol. 30:211-218.

RANA, S. V. S., AND S. KUMAR. 1997. Histopathological studies on the liver of rats treated individually and with a combination of xylene, toluene and methyl alcohol. J. Env. Biol. 18:185-190.

WEATHERHEAD, P. J., F. E. BARRY, G. P. BROWN, AND M. R. L. FORBES. 1995. Sex ratios, mating behavior and sexual size dimorphism of the northern water snake, Nerodia sipidon. Behav. Ecol. Sociobiol. 36:301-311.

TABLES

TABLE 1. Frequency at which 35 Uta stansburiana from the southern Nevada region spent the night above or below ground after having been marked, or not-marked, with xylene-based paint-pens. Data were summarized for all lizards, for juveniles (SVL ≤ 39 mm), and for adults (SVL > 39 mm).

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                       All Lizards     Juvenile       Adult 
                       -----------   -----------    ----------- 
Sleeping Position      Marked Not     Marked Not    Marked Not
-----------------      ------ ---     ------ ---    ------ ---
  Above Ground          10     2        8     1       2     1
  Below Ground          11    12        3     4       8     8
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