Monitoring population productivity in the saiga antelope

Abstract

Effective conservation requires a good understanding of factors causing variation in population growth rate. We here analyse the relationship between female age and fecundity in the saiga antelope Saiga tatarica tatarica, a critically endangered ungulate of the Eurasian steppes and semideserts, at both individual and population levels. Annual variation in age structure and twinning rates was investigated using long-term datasets, sampling a total of 3308 females in four populations over more than 40 years. Further, a new non-invasive method is presented, estimating twinning rates from both calves and placentas encountered during calving aggregation transects. At an individual level, the most parsimonious model for twinning rates included three age classes (1, 2 and Z3 years); however, the model with only two classes (1 and Z2 years) was competitive and particularly useful for monitoring because these two age classes can reliably be determined by direct observation in the field. Among yearlings, 77.4% were fecund and 11.7% twinned, whereas among older females 94.6% were fecund and 72.6% twinned. At a population level, annual variation in age structure (proportion Z2 years) correlated well with annual variation in twinning rate except in the north-west PreCaspian population. Our results suggest that the recent poaching-driven collapse in saiga numbers has potentially resulted in reductions in fecundity, which will have an impact on population growth rate. Our results highlight the potential for monitoring of twinning rate using non-invasive calving aggregation transects as a cost-effective additional tool to population counts for monitoring the status of this critically endangered species. These monitoring methods are also potentially transferable to other ungulate species.

Conserving a moving target: planning protection for a migratory species as its distribution changes

“…Recent studies based on analysis of time series satellite data also predict a decline in productivity across the saiga range (de Beurs, Wright & Henebry 2009; Zhao & Running 2010). Kazakhstan is currently undergoing rapid development, including new infrastructure, urban growth and human population increases, which are likely to change patterns of human disturbance, and together with increasing wealth, may affect poaching pressure (Kühl et al. 2009).…”

Fecal hormones as a non‐invasive population monitoring method for reindeer

“…Management and conservation of wild animals requires knowledge of demographic and population parameters, including sex ratio, age structure, and reproductive status of the individuals (Mysterud and Østbye 2006, Kuhl et al 2009). Age structure varies within populations over time, and knowledge of these differences is critical for exploring trends in recruitment, population growth, survival, senescence, and reproductive status (Reilly 2002, Festa‐Bianchet et al 2003).…”

“…Age structure varies within populations over time, and knowledge of these differences is critical for exploring trends in recruitment, population growth, survival, senescence, and reproductive status (Reilly 2002, Festa‐Bianchet et al 2003). Age‐specific reproduction alone could aid our understanding of population performance and dynamics and could help predict future trends in population size (Gaillard et al 2000, DelGiudice et al 2007, Kuhl et al 2009). Often, the techniques involved in gathering such information are stressful for the study animal (Côté et al 1998, Cattet et al 2008, Omsjoe et al 2009) and can be extremely costly (Haigh 1979, Valkenburg et al 1983).…”

Factors affecting survival and cause-specific mortality of saiga calves in Mongolia

“…First-year females of saiga tend to give birth to 1 calf, whereas older females generally give birth to twins (Fadeev and Sludskii 1982), and when modeled, female age and year helped explain twinning rates in the saiga population in the Pre-Caspian region (Kühl et al 2009). Unfortunately, we did not know ages of adult females our study.…”