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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
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
100815, an adult
in Aransas National
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.
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
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
Rood, J.P. 1958. Habits of the short-tailed shrew in captivity. Journal of Mammalogy 39:499–
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
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