Parturition and bed site selection of bighorn sheep at local and landscape scales

Abstract

Selection of parturition sites by wild ungulates involves trade-offs between maximizing forage quality or availability and minimizing predation risk. Previous studies documenting critical lambing habitat of bighorn sheep (Ovis canadensis) have relied on visual observations that can lead to biased results. We used vaginal implant transmitters (VITs) and intensely monitored radiocollared females to 1) accurately identify parturition events for bighorn sheep; 2) quantify habitat selection for parturition events at the macro- and microhabitat scales; and 3) quantify habitat selection of neonate lamb (≤24 hr old) bed sites at the microhabitat scale in the Black Hills, South Dakota. From 2010–2012, we documented 43 parturition and 47 lamb bed sites for microhabitat analysis, and incorporated an additional 28 capture sites where lambs were ≤24 hours old for macrohabitat analysis (n = 71). We found females equipped with VITs increased our ability to identify parturition events 2-fold (67%) over intensely monitored radiocollared ewes (33%), and 82% (58/71) of parturition events occurred outside of previously delineated lambing habitat. Results of model-averaged generalized estimating equations revealed bighorn sheep females selected for relatively flat spaces within rugged terrain, areas that were close to perennial streams, south and west facing slopes, and against anthropogenic disturbance. At the microhabitat scale, neonate lambs tended to select for greater cover in the uphill and downhill directions, and against north facing slopes. We hypothesize the patterns of selection we observed were related to predator-avoidance strategies and increased solar radiation. We recommend managers reassess designated critical lambing habitat previously defined by visual observations, or consider more broad-scale temporal closures to protect parturient habitat. © 2015 The Wildlife Society.