DOI: 10.5061/dryad.4xgxd2581
title: Data from: Greater sage-grouse survival varies with breeding season events in West Nile virus non-outbreak years

description: Greater Sage-Grouse (Centrocercus urophasianus) are a species of
 conservation concern and are highly susceptible to mortality from West
 Nile virus (WNV). Culex tarsalis, a mosquito species, is the suspected
 primary vector for transmitting WNV to sage-grouse. We captured,
 radio-tagged, and monitored female sage-grouse to estimate breeding season
 (April 15‒September 15) survival 2016-2017. Deceased sage-grouse were
 tested for active WNV; live captured and hunter harvested sage-grouse were
 tested for WNV antibody titers. Additionally, we trapped mosquitoes with
 CO2 baited traps 4 nights per week (542 trap nights) to estimate WNV
 minimum infection rate (MIR). Eight sage-grouse mortalities occurred
 during the WNV seasons of 2016 and 2017; 5 had recoverable tissue, and one
 of 5 tested positive for WNV infection. Survival varied temporally with
 sage-grouse biological seasons, not WNV seasonality. Survival was 0.68
 (95% CI= 0.56–0.78; n=74) during the reproductive season (April
 1−September 15). Mammalian predators were the leading suspected cause of
 mortality (40%), followed by unknown cause (25%), avian predation (15%),
 unknown predation (15%), and WNV (5%). These results indicate WNV was not
 a significant driver of adult sage-grouse survival during this study.
 Three sage-grouse (1.9%; 95% CI=0.5−5.9%) contained WNV antibodies. We
 captured 12,472 mosquitoes of which 3,933 (32%) were Culex tarsalis.
 Estimated WNV MIR of Culex tarsalis during 2016 and 2017 was 3.3 and 1.6,
 respectively. Our results suggest sage-grouse in South Dakota have limited
 exposure to WNV, and WNV was not a significant source of sage-grouse
 mortality in South Dakota during 2016 and 2017. Based on our finding that
 a majority of sage-grouse in South Dakota are susceptible to WNV
 infection, WNV could potentially have an impact on the population during
 an epizootic event; however, when WNV is at or near endemic levels, it
 appears to have little impact on sage-grouse
 survival.      
description: We annually captured breeding-age male and female sage-grouse
 near active leks March−May, as well as at high sage-grouse use areas in
 August and September using nocturnal spotlighting and a long-handled net
 (Giesen et al. 1982, Wakkinen et al. 1992). We aged and sexed captured
 sage-grouse based on plumage and morphological characteristics (Crunden
 1963, Beck et al. 1975, Bihrle 1993). We fit female sage-grouse with a
 21.6 g necklace-type Very High Frequency (VHF) radio-tag with an 8-hour
 mortality switch (model A4060, Advanced Telemetry Systems, Isanti, MN,
 USA). We weighed all birds at the time of capture to ensure that
 radio-tags were less than 3% of body weight (Kenward 2001). Both male and
 female sage-grouse were fit with a uniquely numbered aluminum butt-end leg
 band (National Band & Tag Company). All animal handling procedures
 were approved by the Institutional Animal Care and Use Committee at South
 Dakota State University (IACUC approval # 15-074A). We
 monitored VHF signals of all radio-tagged females twice weekly from April
 15– June 14 and daily from June 15- September 15. Daily monitoring allowed
 us to reduce bias associated with lag-time in recovery of corpses in
 determining true cause-specific mortality (Bumann and Stauffer 2002,
 Stevens et al. 2011) as well as increase our probability of finding fresh
 tissue for WNV testing. If a sage-grouse radio-tag signal was detected on
 mortality mode, the sage-grouse and VHF radio-tag were recovered
 immediately, and cause of death was investigated. To
 test for previous WNV infection in sage-grouse, we used a 22-gauge needle
 to collect 1 ml of blood from the brachial vein (Gregg et al. 2006) of
 captured sage-grouse. In addition to captured sage-grouse, we
 opportunistically collected blood from the hearts of harvested sage-grouse
 during a limited hunting season in 2016. Whole blood was placed in a 2 ml
 blood tube with a clot activator, then centrifuged within 12 hours of
 collection. Serum was decanted, frozen, and maintained at -20°C until
 shipped for testing (Walker et al. 2007). Serum samples were tested for
 WNV antibodies using a Plaque-reduction neutralization assay at Cornell
 University’s Animal Health Diagnostic Center (Naugle et al. 2004, 2005,
 Walker et al. 2007). Samples were considered negative for WNV antibodies
 if titers were not detected at the minimum serum dilution (1:10).
 Radio-tagged sage-grouse were recaptured at the conclusion of the study.
 Blood samples were collected and tested for WNV antibodies again;
 radio-tags were removed. This allowed us to document any radio-tagged
 sage-grouse that had become infected with WNV, developed antibodies, and
 survived the duration of the study. To test for active
 WNV infection in dead sage-grouse, we recovered any available tissues
 (intestines, proventriculus, liver, kidney, lung, heart and brain) from
 mortalities that occurred from June 1 ‒ September 15. Recovered tissues
 were frozen until testing for presence of WNV using a Reverse
 Transcriptase-PCR Assay at Cornell University’s Animal Health Diagnostic
 Center (Porter et al. 1993, Shi 2001). Adult mosquitoes
 were trapped June 1‒September 15 using standard miniature light traps with
 photocell-controlled CO₂ release (John W. Hock Company; Model 1012.CO2) 4
 nights per week. CO₂ traps were set to deliver 0.5L CO₂/min (Vincent et
 al. 2020). Captured mosquitoes were frozen and sorted to species. Female
 mosquitoes contribute to the transmission of WNV due to their requirement
 to consume blood meals prior to oviposition (Hubert et al. 1954) and
 although there are examples of male mosquitoes infected with WNV (Anderson
 et al. 2006, Unlu et al. 2010), they are typically not of interest when
 researching WNV (US EPA 2017). Therefore, we identified female mosquitoes
 and sorted each to species based on morphological characteristics using a
 dichotomous identification key (Darsie and Ward 2005). Female Culex
 tarsalis were placed in vials of up to 50 individuals, homogenized, and
 tested for WNV using a TaqMan Reverse Transcriptase-PCR Assay, as
 described in Lanciotti et al. (2000) with slight modifications.
description: Readme files are included for each sub dataset.