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Date of birth, litter and neonate size of a diamondback water snake, Nerodia rhombifer, from southernmost Texas.

Reports of the time of birth of the diamondback water snake, Nerodia rhombifer, place the beginning of litter production in August (Wright & Wright 1957; Collins 1974; Tennant 1985; Dundee & Rossman 1989). Ford et al. (1990) report litters from northeastern Texas on 17, 20 and 23 August. During the course of live-trapping N. rhombifer for a study of pesticide contamination at Santa Ana National Wildlife Refuge, Hidalgo County, Texas, a female (SVL 1.15 m, wt 2.3 kg) was captured during the night of 20 July 1995 and held in the laboratory for blood sampling. This female gave birth to a litter of 39 offspring on 21 July 1995. This date of birth is the earliest known record for the species. During the night of 20 July 1995 neonates were observed at Willow Lake within the Santa Ana National Wildlife Refuge, so the birth in captivity is not considered an isolated event.

Three of the 39 neonates were either born dead or died before they were measured. Mean snout-vent length (SVL) of all 39 neonates was 228 mm (range 202-240, SD = 9.6, CV = 4.2). This is significantly smaller (P < .01, 523 df) than the mean of 246.1 mm (SE = 0.6) reported by Plummer (1992) for 486 neonates from Arkansas. Ford et al. (1990) reported a mean SVL of 214.8 mm for 55 neonates (two litters) from northeastern Texas. The neonates from southernmost Texas were significantly larger (t=8.57, 92 df, P<.001) than the neonates from northeastern Texas. Aldridge et al. (1995) reported a mean SVL of 213 mm (range 204-221) for neonates from Veracruz, Mexico, but did not give a sample size or a measure of variance. Consequently, a statistical comparison of neonate SVL of these specimens is not possible.

The data reported here are the first available for a subtropical population of N. rhombifer. The information on geographic variation in litter size suggests that there is no clinal latitudinal variation in neonate size in N. rhombifer.

The litter size (39) observed in this study is beyond the range (8-36) reported for N. rhombifer from Veracruz, Mexico, (Aldridge et al. 1995) and it is larger than the litter sizes of 26, 33, and 37 reported by Ford et al. (1990) for three litters from northeastern Texas. Conversely, it is within the ranges reported by Cagle (1937) for Tennessee (13-42) and Plummer (1992) for Arkansas (12-48). Aldridge et al. (1995) reported that clutch size was significantly smaller in the tropical Veracruz, Mexico, population than in temperate populations. While caution should be used in drawing inferences based on the meager data currently available for Texas populations, it appears that litter size in N. rhombifer from southernmost Texas may be typical of that of temperate populations and significantly larger than that of tropical populations.


We are grateful to B. Autry, T. Hyde and J. Gable for assistance in the field and laboratory.


Aldridge, R. D., W. P. Flanagan & J. T. Swarthout. 1995. Reproductive biology of the water snake Nerodia rhombifer from Veracruz, Mexico, with comparisons of tropical and temperate snakes. Herpetologica, 51:182-192.

Cagle, F. R. 1937. Notes on Natrix rhombifera as observed at Reelfoot Lake. J. Tennessee Acad. Sci., 12:179-185.

Collins, J. T. 1974. Amphibians and reptiles in Kansas. Univ. Kansas Mus. Nat. Hist. Public Education Series No. 1. ix + 283 pp.

Dundee, H. A., & D. A. Rossman. 1989. The amphibians and reptiles of Louisiana. Louisiana State Univ. Press, Baton Rouge. xi + 300 pp.

Ford, N. B., V. A. Cobb & W. W. Lamar. 1990. Reproductive data on snakes from northeastern Texas. Texas J. Sci., 42(4):355-368.

Plummer, M. V. 1992. Relationships among mothers, litters, and neonates in diamondback water snakes (Nerodia rhombifer). Copeia, 1992:1096-1098.

Tennant, A. 1985. A field guide to Texas snakes. Texas Monthly Press, Austin, Texas. 1-260 pp.

Wright, A. H. & A. A. Wright. 1957. Handbook of snakes of the United States and Canada. Vol.I. Comstock Publ. Associates, Ithaca, New York. xviii + 564 pp.

Frank W. Judd and Martin Bray

Department of Biology, University of Texas-Pan American, Edinburg, Texas 78539 and U.S. Fish and Wildlife Service, Rt. 2 Box 202A, Alamo, Texas 78516
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Title Annotation:GENERAL NOTE
Author:Judd, Frank W.; Bray, Martin
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Feb 1, 1996
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