Temporal dynamics of sagebrush songbird abundance in relation to energy development

Spatial aspects of wildlife responses to human-induced habitat change have been examined frequently, yet the temporal dynamics of responses remain less understood. We tested alternative hypotheses for how the abundance of a suite of declining songbirds in relation to energy development changed over time. We conducted point counts at two natural gas fields during two periods spanning a decade (2008–2009 and 2018–2019), and compared the abundance of sagebrush songbirds across a gradient of surface disturbance between study periods (trend-by-time). We also assessed changes in the abundance of birds between study periods relative to additional development that had occurred (trend-over-time). We predicted that abundance responses to surface disturbance would be more negative during the second period, regardless of additional disturbance that had occurred, because of previously observed inverse relationships between surface disturbance and nest survival at our sites. Contrary to our predictions, abundance responses attenuated by the second time period for two of three species, Brewer's sparrow and sage thrasher (the latter at one energy field only). Sagebrush sparrow abundance, however, consistently decreased with surface disturbance within and between periods. Sage thrasher abundance consistently decreased with surface disturbance at one of the gas fields, and the probability of colonization by thrashers between study periods was lower where additional surface disturbance had occurred. Our results highlight the importance of revisiting wildlife responses to anthropogenic habitat changes over time, to clarify the severity and longevity of effects.