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radio-telemetry at the Redbank Reserve
near Macraes Flat, Central Otago. She
tracked 13 skinks from December
2003–April 2004 for 26–111 days.
Neither distances moved nor frequencies
of movements differed significantly
between males and females. Home range

estimates (using the 100% minimum
convex polygon method) ranged from
200–5,400 m2, with male home ranges
significantly larger than those of females,
and those of non-gravid females signifi-
cantly larger than those of gravid females.
Home range overlap was substantive and

interactions between individuals
occurred frequently. Capturing animals
increased frequency of movements, espe-
cially on days immediately following cap-
ture. Data generated by this study will be
incorporated into a management plan for
the species.

IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 197NATURAL HISTORY RESEARCH REPORTS

Desert Tortoise 
Hibernation

NUSSEAR ET AL. (2007. Copeia 2007:
378–386) examined the onset, duration,
and termination of hibernation in Desert
Tortoises (Gopherus agassizii) over several
years at multiple sites in the northeastern
part of their geographic range in Utah,
Arizona, and Nevada, and recorded the
temperatures experienced by tortoises
during winter hibernation. The timing of
hibernation by Desert Tortoises differed
among sites and years. Environmental
cues acting over the short-term did not
appear to influence the timing of the
hibernation period. Different individual
tortoises entered hibernation over as
many as 44 days in the fall and emerged
from hibernation over as many as 49
days in the spring. This range of variation
in the timing of hibernation indicated a
weak influence at best of exogenous cues
hypothesized to trigger and terminate
hibernation. Regional trends do appear,
as hibernation tended to begin earlier
and continue longer at sites that were
higher in elevation and generally cooler.
The emergence date was generally more
similar among study sites than the date of
onset. While the climate and the subse-

quent timing of hibernation differed
among sites, the average temperatures
experienced by tortoises while hibernat-
ing differed by only about five degrees
from the coldest to the warmest site.

Feeding Ecology of 
Rattleless Rattlesnakes

Crotalus catalinensis is a rattleless rat-
tlesnake endemic to Santa Catalina
Island, in the Gulf of California, Mexico.
Some authorities have hypothesized that
the lack of a rattle in this species is a
stealth adaptation for hunting birds in
vegetation. AVILA-VILLEGAS ET AL.
(2007. Copeia 2007: 80–84) provided

detailed data on the diet of these snakes
from samples obtained during nine trips
to the island in 2002–2004. Over two-
thirds (70%) of the diet was composed of
the Santa Catalina Deer Mouse
(Peromyscus slevini). The remaining prey
were lizards (Dipsosaurus catalinensis, Uta
squamata, and Sceloporus lineatulus). The
diet shifted ontogenetically, and feeding
activity was greater during the dry sea-
son. The diet of this species is only a
small subset of the diet of its supposed
closest relative, C. ruber, probably as a

result of limited prey diversity on the
island. The lack of birds in the diet
argues against the hypothesis relating the
lack of a rattle with a stealth hunting
technique for birds in vegetation.
However, because P. slevini is partially
arboreal, the lack of a rattle might be an
adaptation for stealth hunting for mice in
vegetation.

Habitat Affects 
Predator Attack Frequencies

Predators use characteristics such as pat-
tern and shape in forming search images
of prey, thereby influencing the evolution
of prey morphology. In lizards, sit-and-
wait foraging species are thought to have
body shapes that enhance their ability to
remain cryptic to predators. Structurally
complex habitats provide more opportu-
nities for prey to avoid detection, thus
predator foraging efficiency is predicted
to be higher in structurally simple habi-
tats. SHEPARD (2007. Herpetologica 63:
193–202) used clay lizard models to test
whether predation varies among lizards
with different body shapes and whether
predation varies among habitats in the
Brazilian Cerrado with different struc-
tural characteristics. Predator attack fre-
quency was highest in the most struc-
turally complex habitat, but the
probability of being attacked was higher
in more open microhabitats. Attack fre-
quencies did not differ significantly
among the four lizard model shapes.
Lizards and birds were the main attackers
of models, and attacks were primarily
directed toward the models’ heads.
Results demonstrated that predator-prey
interactions are largely influenced by the
environmental context and scale, and
that body shape alone does not efficiently
promote crypsis.

N A T U R A L  H I S T O R Y  R E S E A R C H  R E P O R T S

Local climate affected timing of hibernation,
but average temperatures experienced by
hibernating Desert Tortoises (Gopherus agas-
sizii) differed very little.

TH
O

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W

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T,
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Rattleless Santa Catalina Island Rattlesnakes
(Crotalus catalinensis) feed primarily on mice
and lizards, arguing against the hypothesis
that the lack of a rattle facilitates stealthy
hunting for birds in vegetation.

L.
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M
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