Changes in reptile populations in the Snake River Birds of Prey Area, Idaho between 1978--1979 and 1997--1998: The effects of weather, habitat and wildfire

Southwestern Idaho has the highest state reptile diversity, yet there are indications that reptile declines may have occurred there. To assess this possibility, I determined if temporal changes in reptile populations had occurred in the Snake River Birds of Prey Area (SRBPA). Drift fence trapping arrays were used to measure reptile status during the summers of 1997–98, and these data were compared to an historic data set collected in 1978–79 at the same 24 study sites. Habitat variables were also measured in 1998 and correlated with reptile status. I made comparisons of habitat and reptile status between shrub sites and sites that had burned and were converted to exotic annual dominated sites (burn-conversion sites). Contrasts between shrub sites and burn-conversion sites revealed that the abundance of lizards and a lizard-eating snake was significantly less at bum-conversion sites, suggesting that ground foraging lizards and at least one of their reptile predators ( Masticophis taeniatus) may have declined in other areas throughout the SRBPA where comparable changes have occurred. In addition, lizards were negatively correlated with a number of habitat variables indicative of disturbance, such as increased herbaceous plant cover, greater abundance of cheatgrass and other exotic annuals, and decreases in shrub cover, open soil and cryptogamic crusts. Snakes demonstrated few habitat correlations with the exception of Coluber constrictor, which in contrast to lizards, was positively correlated with some of the same “disturbance” variables. Although there was little change in species occurrence for the SRBPA, significant differences existed between 1998 and the other two periods (1978–79 and 1997), and were likely due to the effects of weather. Awareness of wildfire-induced changes is important, as knowledge of the status of reptiles in southwestern Idaho and their response to large-scale losses of native vegetation was previously nonexistent. In addition, if biodiversity and species abundance continue to decline, it will become increasingly important to understand the factors that result in negative impacts. Knowledge of these factors may foster increased monitoring of populations that were formerly assumed stable, and may add impetus to efforts aimed at minimizing additional habitat loss.