DO YOU WANT TO KNOW ABOUT TORTOISES?
loves tortoises. And a new book has lots of advice about how we can
protect these engaging reptiles. "Biology and Conservation of North
American Tortoises" edited by David C. Rostal, Earl D. McCoy, and
Henry R. Mushinsky (Johns Hopkins University Press, 2014) answers myriad
questions about tortoises. In fact, the 33 experts who wrote the 18
chapters of the book answer more questions about the conservation and
ecology of tortoises than the general public has even thought of.
have a pretty clear picture of this distinctive group of turtles when
they think of the giant Galapagos tortoises. In the southeastern United
States, particularly parts of Alabama, Georgia, Florida, and South Carolina,
many folks are familiar with the native gopher tortoises, which dig
long underground burrows that are often used for shelter by other animals.
Out West, in arid regions of southern California, Nevada, Utah, and
Arizona, desert tortoises are natural inhabitants with which many people
are familiar. A less well known U.S. species is the Texas tortoise,
aka Berlandier's tortoise, found in southern Texas. Desert tortoises
and Texas tortoises also extend south of the border into the Mexican
deserts. As indicated in the title, the book covers North America, hence
the inclusion of the Bolson tortoise, which is restricted to the Chihuahuan
Desert in Mexico.
work addresses topics of interest to research biologists who study tortoises:
the fossil record, reproductive traits, growth rates, movement patterns,
and general life history. A chapter on social behavior of these captivating
creatures is of particular interest. The authors consider in what ways
the communication patterns of these "highly social vertebrates"
affect how they distribute themselves within a tortoise colony, what
the mating structure will be, and what strategies they use for avoiding
predators. The final chapter, "Threats and Conservation Needs for
North American Tortoises," addresses tough questions about what
must be done to ensure the survival of these marvelous animals.
facts noted in the book make for some interesting speculation. One is
related to the incubation period of eggs of desert and gopher tortoises.
Both have been studied extensively enough for scientists to know that
the eggs can incubate and hatch in as few as 10 weeks if temperatures
are high. Eggs incubating at cooler temperatures can take more than
four months to hatch. Another set of data for North American tortoises
confirms that eggs incubating at high temperatures are more likely to
produce females whereas hatchlings from eggs experiencing low temperatures
are more likely to be males. Thus the actual sex ratio in a tortoise
population could become highly skewed because of changes in environmental
temperatures. Extensive variation can occur with such biological phenomena.
However, the implications of how tortoise populations might respond
to climate change scenarios that could result in higher temperatures
during incubation are worth considering.
consider global warming a major danger to wildlife in North America
and throughout the world. But the most serious threats to tortoises
- and indeed animals everywhere - are much more imminent and clearly
identifiable as a result of habitat destruction. As the chapter on habitat
characteristics of tortoises points out, "Most threats to tortoise
habitat generally can be attributed directly to human causes that include
urbanization, agriculture, and the building of highways." Another
less tangible detrimental impact on natural populations of tortoises
is the release into wild areas of pet tortoises. These discarded pets
may carry contagious diseases, including an upper respiratory tract
infection that can be passed on to wild tortoises.
give unquestionable proof that North American tortoises are declining
at an alarming rate. Ironically, most "are protected in whole or
in part by international, federal, and state regulations." However,
as the authors note, these official designations have not "resulted
in the regulations and enforcement essential" to actually protect
the tortoises. The book is to be commended for providing evidence that
more stringent conservation measures are needed on behalf of U.S. and
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