Foraging at the wildland–urban interface decouples weather as a driver of recruitment for desert bighorn sheep

Abstract

A growing number of ungulate populations are living within or near the wildland–urban interface. When resources at the interface are of greater quality than that of adjacent natural habitat, wildlife can be attracted to these developed areas. Little is known about how use of the wildland–urban interface by wildlife may affect vital rates. Under natural conditions, recruitment by desert bighorn sheep (Ovis canadensis nelsoni) correlates with variation in the timing and amount of rainfall that initiates and enhances growth of annual plant species. However, for populations that forage in developed areas, this relationship may become decoupled. In the River Mountains of Nevada, USA, desert bighorn sheep have been feeding in a municipal park at the wildland–urban interface since its establishment in 1985. Approximately one‐third of the population now uses the park during summer months when nutritional content of natural forage is low. We hypothesized that use of this municipal area, with its abundant vegetation and water resources, may have decoupled the previous relationship between precipitation and lamb recruitment. We assessed variables known to affect lamb recruitment before (1971–1986) and after (1987–2006) establishment of the park using linear regression models. Our top candidate model for the pre‐park period indicated that total November precipitation was the greatest driver of lamb recruitment in this population. After park establishment, this relationship became decoupled because lamb recruitment was no longer driven by weather variables. These results raise questions about the effects of decoupling drivers of population growth and maintaining natural populations near urban areas. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Using satellite‐derived estimates of plant phenological rhythms to predict sage‐grouse nesting chronology

“…Across years, we would expect these populations to exhibit boom and bust dynamics in nest success, reflecting the erratic conditions under which they live. Similar patterns have been described for desert ungulates, in which a highly variable growing season promotes a long birthing season with only a small portion of any cohort surviving in a given year (Bunnell, 1982; Longshore, Lowery, & Cummings, 2016; Stoner et al., 2016). Low‐elevation populations are more vulnerable to poor recruitment, with future changes likely to exacerbate current trends.…”

Artificial nightlight alters the predator–prey dynamics of an apex carnivore

“…Deer at the wildland–urban interface were primarily active at night when nightlight exposure is most perceptible. These areas with elevated nightlight exposure also contain watered lawns, city parks and agriculture which provide elevated levels of greenness, used for forage and cover (Longshore et al 2016).…”

Survival and cause‐specific mortality of desert bighorn sheep lambs

“…Neonates that are heavier at birth typically have higher survival rates that those born lighter (Thorne et al , Fairbanks , Keech et al , Cook et al , Heffelfinger et al ). Several studies have reported a positive relationship between fall lamb:adult female ratios in desert bighorn sheep and rainfall during the previous winter period (Douglas and Leslie , Wehausen et al , Douglas , Wehausen , Longshore et al ), suggesting a link between rainfall during late gestation and early post‐parturition, and juvenile recruitment. Rainfall during the second year of our study when we observed very low lamb survival (i.e., 20%) was 68% below average compared to the first year when lamb survival was around 70% and rainfall during late gestation was almost 3 times higher than normal.…”