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Texas Shrews (Blarina hylophaga) Lacking External Eye Openings
Melissa C. Jones, Thomas R. Simpson, Richard W. Manning, and Michael R.J. Forstner

Southeastern Naturalist, Volume 6, Number 4 (2007): 752–754

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2006 NORTHEASTERN NATURALIST 13(1):39–42 Texas Shrews (Blarina hylophaga) Lacking External Eye Openings Melissa C. Jones1,2,*, Thomas R. Simpson1, Richard W. Manning1, and Michael R.J. Forstner1 Abstract - Shrews are insectivorous opportunistic foragers occupying moist habitats characterized by high vegetative composition. Shrews characteristically have poorly developed eyesight and rely on olfactory and auditory senses for efficient foraging. Two Blarina hylophaga (Elliot’s short-tailed shrew) recently trapped in East Texas did not have externally visible eyes. Further examination during specimen preparation revealed both had developed eyes, but lacked developed, opened, or functional eyelids. A third shrew, collected in Bastrop County, TX, had developed eyes and eyelids, however, the external openings were abnormally small. All three shrews were adults and alive in traps, suggesting no ill effects due to the reduction or absence of eye openings and further suggesting little or no effect on the survival of these individuals. Shrews are insectivorous opportunistic foragers with high metabolic rates (Martinsen 1969) requiring constant foraging day and night (Whittaker and Feldhamer 2005). Shrews characteristically have poorly developed eyesight (Churchfield 1990), but still hunt efficiently due to their well developed olfactory and auditory senses. Branis (1981) observed that shrews did not exhibit a significant response to light stimulus, and Churchfield (1990) concluded that although sight might record light intensity, it is not a prime sense used in foraging (Rood 1958). Their sense of smell, however, allowed shrews to recover 50% of prey buried under 120 mm of soil (Churchfield 1990). Shrews further enhance their foraging efficiency through the use of auditory cues to investigate the source of rustling sounds (Pernetta 1977). Additionally, a poorly developed form of echolocation has been recorded in various species of Blarina, Sorex, and Cryptotis (Churchfield 1990, Gould et al. 1964) and is used for navigation and possibly for prey location. Through the use of low-intensity and high-frequency pulses (Gillihan and Foresman 2004), shrews can supplement their olfactory and auditory abilities to adjust to their surroundings (Buchler 1976). Therefore, successful detection of prey depends on the combined use of many senses, including sight, sound, and smell, with sight being the least-effective sensory tool. In this report, we describe three individual Blarina hylophaga Elliot (Elliot’s short-tailed shrew) that appeared to lack externally visible eyes. Further examination during specimen preparation revealed two shrews had developed eyes, but lacked developed, opened, or functional eyelids. The third shrew had developed and opened eyes, but their functionality was questionable due to their extremely small size. This note is the first published report of this phenomenon in Elliot’s short-tailed shrew or any species of shrew. Methods. Trapping was conducted in Aransas County during summer and autumn of 2003 and in Bastrop County 2001–2003 and May 2005–April 2006. Shrews were captured in pitfall traps (18.93 liter) on 400-m linear drift fences or 100-m radius Y-shaped drift fence arrays (Reilly et al. 2005) and in Sherman traps (50.8 x 63.5 x 165.1 mm). Data collection included species identification, sex, total length, tail length, hind-foot length, ear length, and weight. Animals were categorized as adult or juvenile by comparison with limits of adult total length and pelage description given by Schmidly (2004). Individuals of the genus Blarina were identified based on morphological features described by Reilly et al. (2005). Observations. On 2 February 2003 in Bastrop County, a male Elliot’s shorttailed shrew was collected 32 km west of Smithville, TX. Upon capture, it was Notes of the Southeastern Nat u ral ist, Issue 6/4, 2007 752 2007 Southeastern Naturalist Notes 753 noted that no external eyes were visible. However, further examination during specimen preparation exposed developed eyes beneath undeveloped eyelids and external eye openings (Fig. 1). This specimen had a total length of 92 mm, a tailvertebrae length of 19 mm, a hind-foot length of 12 mm, and a weight of 7.0 g. This specimen (TTU-M 100806), and the others, were deposited in the mammal collection of the Natural Science Research Laboratory (NSRL) at Texas Tech University. The second Elliot’s short-tailed shrew was collected on 12 June 2003 in Aransas County, on Aransas National Wildlife Refuge on Walker Mill Road. This female specimen (TTU-M 100815) also lacked external eye openings (Fig. 2). The shrew had a total length of 88 mm, a tail-vertebrae length of 18 mm, a hind-foot length of 13 mm, and a weight of 6.8 grams. A third specimen of B. hylophaga (RWM 3834), collected in Bastrop County on 22 January 2006, exhibited developed eyes and eyelids. However, the external eye openings were abnormally small, and were probably not functional. This male specimen had a total length of 88 mm, a tail-vertebrae length of 20 mm, a hind-foot length of 11 mm, and a weight of 7.0 grams. Discussion. Shrews and other semifossorial mammals have reduced eyes and poor eye sight (Burda et al. 1990, Pearson 1984, Stein 2000). Borghi et al. (2002) suggest habitat, diet, and burrowing activities may influence the size of eyes in small mammals, concluding that eye size was negatively related to the amount of digging and positively related to the availability of above-ground food resources. Other Figure 1. Photograph taken during preparation of TTU-M 100806, an adult Blarina hylophaga plumbea (Elliott’s short-tailed shrew) collected 32 km west of Smithville, TX, on 2 February 2003. Figure 2. Photograph taken during preparation of TTU-M 100815, an adult Blarina hylophaga plumbea (Elliot’s short-tailed shrew) collected in Aransas National Wildlife Refuge, Aransas County, TX, on 12 June 2003. 754 Southeastern Naturalist Notes Vol. 6, No. 4 morphological adaptations likely to protect the eyes while burrowing, such as eye retraction, hyperactivity of lacrimal glands, and thickened cornea, have also been observed in fossorial and semifossorial mammals (Burda et al.1990, Stein 2000). Morphological eye adaptations in subterranean small mammals have been commonly documented. This note is the first published report of under-developed and non-functional eyes in shrews. Because all three animals were adults and alive in traps, we conclude that there were no negative consequences due to the reduction or absence of eye openings in these individuals. We suggest that the absence of eye openings would have little direct effect on the survival of these individuals because sight plays a minor role in the foraging of shrews. Acknowledgments. Funding was provided by Texas Parks and Wildlife Department, Bastrop State Park and Texas State University-San Marcos. We thank Sue Reilly for providing the Aransas County, TX, specimen. The use of traps and trapping for research was sanctioned by Texas Parks and Wildlife permit TE814933-3, TE039544-0, and 03FE018D78-03 from the Texas State University-San Marcos Institutional Animal Care and Use Committee. Literature Cited Borghi, C.E., S.M. Giannoni, and V.G. Roig. 2002. Eye reduction in subterranean mammals and eye protective behavior in Ctenomys. Journal of Neotropical Mammalogy 9:123–134. Branis, M. 1981. Morphology of the eye of shrews (Soricidae, Insectivora). Acta Universitas Carolinae-Biologica 11:409–445. Buchler, E.R. 1976. Experimental demonstration of echolocation by the wandering shrew (Sorex vagrans). Animal Behavior 24:858–873. Burda, H., V. Bruns, and M. Muller. 1990. Sensory adaptations in subterranean mammals. Pp. 269–293, In E. Nevo and O. Reig (Eds.). Evolution of Subterranean Mammals at the Organismal and Molecular Levels. Alan R. Liss, Inc. New York, NY. 422 pp. Churchfield, S. 1990. Natural History of Shrews. Comstock Publishing Associates, Ithaca, NY. Gillihan, S.W., and K.R. Foresman. 2004. Sorex vagrans. Mammalian Species 744:1–5. Gould, E., A. Negus, and A. Novick. 1964. Evidence for echolocation in shrews. Journal of Experimental Zoology A 154:19–38. Martinsen, D.L. 1969. Energetics and activity patterns of short-tailed shrews (Blarina) on restricted diets. Ecology 50:505–510. Pearson, O.P. 1984. Taxonomy and natural history of some fossorial rodents of Patagonia, southern Argentina. Journal of Zoology (London) 202:225–237. Pernetta, J.C. 1977. Anatomical and behavioral specializations of shrews in relation to their diet. Canadian Journal of Zoology 55:1442–1453. Reilly, S.M., R.W. Manning, C.C. Nice, and M.R.J. Forstner. 2005. Systematics of isolated populations of short-tailed shrews (Soricidae: Blarina) in Texas. Journal of Mammalogy 86:887–894. Rood, J.P. 1958. Habits of the short-tailed shrew in captivity. Journal of Mammalogy 39:499– 507. Schmidly, D.J. 2004. The Mammals of Texas. Texas Park and Wildlife Department, Austin, TX. 338 pp. Stein, B. 2000. Morphology of subterranean rodents. Pp. 19–61, In E.A. Lacey, J.L. Patton, and G.N. Cameron (Eds.). Life Underground: The Biology of Subterranean Rodents. The University of Chicago Press, Chicago, IL. 449 pp. Whittaker, J.C., and G.A. Feldhamer. 2005. Population dynamics and activity of southern short-tailed shrews (Blarina carolinensis) in southern Illinois. Journal of Mammalogy 86(2):294–301. 1Department of Biology, Texas State University-San Marcos, San Marcos, TX 78666. 2Current address – 4304 St. Martin Court, Virginia Beach, VA 23455. *Corresponding author - scafi re03_melj@yahoo.com.