Geology topics

Rebekah C. Karsch

Publications and source records attributed to Rebekah C. Karsch.

3 recordsLinked to original sources

USGS2024

Neonate morphometrics and lambing season characteristics of desert bighorn sheep

Desert bighorn sheep ( Ovis canadensis ) populations often occur in remote areas at low densities, leading to gaps in knowledge of life history. In November 2011, we translocated 11 female desert bighorn sheep from the Fra Cristobal Mountains and 9 from Red Rock Wildlife Management Area (RRWMA) to the Peloncillo Mountains in southwestern New Mexico. In December 2012, we captured 21 adult females in the Peloncillo Mountains, 14 of which were recaptured from 2011. We fitted each animal with a very high frequency (VHF) collar and vaginal implant transmitter (VIT) to monitor for parturition. We captured 26 lambs (5 females, 7 males in 2012; 7 males, 7 females in 2013), recorded morphometric measurements and fitted lambs with VHF collars to monitor survival. Over the study, 14 lambs died, with 12 mortalities from predation, one from abandonment, and one from unknown causes. Lambing season was protracted over 3–4 months and survival was unrelated to birth timing. Body mass differences between sex varied by year, suggesting a connection to annual climate. Because most studies focus on captive animals with access to supplemental food, captive lambs may not be representative of free-ranging populations. Thus, we investigated morphological trends in a free-ranging population.

Mammalia↗

USGS2016

Desert bighorn sheep lambing habitat: Parturition, nursery, and predation sites

Fitness of female ungulates is determined by neonate survival and lifetime reproductive success. Therefore, adult female ungulates should adopt behaviors and habitat selection patterns that enhance survival of neonates during parturition and lactation. Parturition site location may play an important role in neonatal mortality of desert bighorn sheep ( Ovis canadensis mexicana ) when lambs are especially vulnerable to predation, but parturition sites are rarely documented for this species. Our objectives were to assess environmental characteristics at desert bighorn parturition, lamb nursery, and predation sites and to assess differences in habitat characteristics between parturition sites and nursery group sites, and predation sites and nursery group sites. We used vaginal implant transmitters (VITs) to identify parturition sites and capture neonates. We then compared elevation, slope, terrain ruggedness, and visibility at parturition, nursery, and lamb predation sites with paired random sites and compared characteristics of parturition sites and lamb predation sites to those of nursery sites. When compared to random sites, odds of a site being a parturition site were highest at intermediate slopes and decreased with increasing female visibility. Odds of a site being a predation site increased with decreasing visibility. When compared to nursery group sites, odds of a site being a parturition site had a quadratic relationship with elevation and slope, with odds being highest at intermediate elevations and intermediate slopes. When we compared predation sites to nursery sites, odds of a site being a predation were highest at low elevation areas with high visibility and high elevation areas with low visibility likely because of differences in hunting strategies of coyote ( Canis latrans ) and puma ( Puma concolor ). Parturition sites were lower in elevation and slope than nursery sites. Understanding selection of parturition sites by adult females and how habitat characteristics at these sites differ from those at predation and nursery sites can provide insight into strategies employed by female desert bighorn sheep and other species during and after parturition to promote neonate survival.

Journal of Wildlife Management↗

USGS2013

Techniques for capturing bighorn sheep lambs

Low lamb recruitment is a major challenge facing managers attempting to mitigate the decline of bighorn sheep ( Ovis canadensis ), and investigations into the underlying mechanisms are limited because of the inability to readily capture and monitor bighorn sheep lambs. We evaluated 4 capture techniques for bighorn sheep lambs: 1) hand-capture of lambs from radiocollared adult females fitted with vaginal implant transmitters (VITs), 2) hand-capture of lambs of intensively monitored radiocollared adult females, 3) helicopter net-gunning, and 4) hand-capture of lambs from helicopters. During 2010–2012, we successfully captured 90% of lambs from females that retained VITs to ≤1 day of parturition, although we noted differences in capture rates between an area of high road density in the Black Hills (92–100%) of South Dakota, USA, and less accessible areas of New Mexico (71%), USA. Retention of VITs was 78% with pre-partum expulsion the main cause of failure. We were less likely to capture lambs from females that expelled VITs ≥1 day of parturition (range = 80–83%) or females that were collared without VITs (range = 60–78%). We used helicopter net-gunning at several sites in 1999, 2001–2002, and 2011, and it proved a useful technique; however, at one site, attempts to capture lambs led to lamb predation by golden eagles ( Aquila chrysaetos ). We attempted helicopter hand-captures at one site in 1999, and they also were successful in certain circumstances and avoided risk of physical trauma from net-gunning; however, application was limited. In areas of low accessibility or if personnel lack the ability to monitor females and/or VITs for extended periods, helicopter capture may provide a viable option for lamb capture.

Colorado;New Mexico;South Dakota↗