Reproductive output and clutch phenology of female Agassiz's desert tortoises (Gopherus agassizii) in the Sonoran Desert region of Joshua Tree National Park

Current Herpetology
By: , and 

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Abstract

Agassiz's desert tortoise (Gopherus agassizii) reaches the southern edge of its range in the Sonoran Desert of California. The reproductive ecology of this wideranging species is understudied here compared to populations in the adjacent Mojave Desert. Understanding potential geographic variation in reproductive ecology is important for effective management of conservation-reliant species like G. agassizii. We studied the fecundity and clutch phenology of female G. agassizii at two study sites in the Sonoran Desert region of Joshua Tree National Park over five years (1997–1999, 2015–2016) spanning two of the strongest El Niño events on record and an epic drought. Across all years, mean clutch size was 4.3±1.5 eggs, mean clutch frequency was 1.78 clutches/female/year, and mean X-ray egg width was 36.51±1.56 mm, all of which are comparable to other published studies both in the Sonoran and Mojave deserts of California. Our results generally support earlier published findings that G. agassizii utilize a bet-hedging strategy of consistently producing small clutches almost every year, even during times of low annual primary productivity. A regionally warmer climate in the Sonoran Desert of California appears to have an effect on the timing of egg production, as the earliest dates of egg visibility in our study (April 6) were approximately two weeks earlier than the earliest dates reported for G. agassizii in the Mojave Desert. Shelled eggs were no longer visible in tortoises after mid-June in all years but the El Niño year 1998, when eggs were visible until mid-July.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Reproductive output and clutch phenology of female Agassiz's desert tortoises (Gopherus agassizii) in the Sonoran Desert region of Joshua Tree National Park
Series title Current Herpetology
DOI 10.5358/hsj.37.40
Volume 37
Issue 1
Year Published 2018
Language English
Publisher BioOne
Contributing office(s) Western Ecological Research Center, Southwest Biological Science Center
Description 18 p.
First page 40
Last page 57
Country United States
State California
Other Geospatial Joshua Tree National Park, Sonoran Desert