We studied a Desert Tortoise (Gopherus agassizii) population at a large wind energy generation facility near Palm Springs, California over six field seasons from 1997 to 2010. We compared growth and demographic parameters to populations living in less disturbed areas; as well as populations of the closely-related and newly-described G. morafkai elsewhere in the Sonoran Desert of Arizona. We marked 69 individuals of all size classes and estimated a population size of 96 tortoises, or about 15.4/km2. Growth rates for males were lower than reported elsewhere, although maximum body size was larger. The smallest female with shelled eggs was 221 mm and males mature at over 200 mm. Mean male size was greater than that of females. The adult sex ratio was not significantly different from unity. Size frequency histograms were similar over time and when compared to most, but not all, G. morafkai populations in the Sonoran Desert. For a cohort of adult females, we estimated mortality at 8.4% annually due, in part, to site operations. This value was low in comparison to many other populations during the same time period. Other than possible differences in growth rate of males and the high survivorship of females, there appear to be few differences between this population and those in more natural areas. The high productivity of food plants at the site and its limited public access may contribute to the overall stability of the population. However, the effects of utility-scale renewable energy development on tortoises in other, less productive, areas are unknown. Additional research (especially controlled and replicated before and after studies) is urgently needed to address this deficiency because of forecasted expansion of utility-scale renewable energy development in the future.
Effects of wind energy production on growth, demography, and survivorship of a desert tortoise population in Southern California with comparisons to natural populations
Title: Effects of wind energy production on growth, demography, and survivorship of a desert tortoise population in Southern California with comparisons to natural populations
June 16, 2011
Journal: Herpetological Conservation and Biology
Publisher: United States Geological Survey
Lovich, J.; Ennen, J.; Madrak, S.; Meyer, K.; Loughran, C.; Bjurlin, C.; Adundel, T.; Turner, W.; Jones, C.; Groenendaal, G. (2011). Effects of wind energy production on growth, demography, and survivorship of a desert tortoise population in Southern California with comparisons to natural populations. Herpetological Conservation and Biology, 6(2), 161-174.