White‐tailed deer neonate survival in the absence of predators

White-tailed deer detection rates increase when coyotes are present

Predator species can indirectly affect prey species through the cost of anti-predator behavior responses, which may involve shifts in occupancy, space use, or movement. Quantifying the various strategies implemented by prey species to avoid adverse interactions with predators can lead to a better understanding of potential population-level repercussions. Therefore, the purpose of this study was to examine predator-prey interactions by quantifying the effect of predator species presence on detection rates of prey species, using coyotes (Canis latrans) and white-tailed deer (Odocoileus virginianus) in Central Appalachian forests of the eastern United States as a model predator-prey system. To test two competing hypotheses related to interspecific interactions, we modeled species detections from 319 camera traps with a two-species occupancy model that incorporated a continuous-time detection process. We found that white-tailed deer occupancy was independent of coyote occupancy, but white-tailed deer were more frequently detectable and had greater detection intensity at sites where coyotes were present, regardless of vegetation-related covariates. In addition, white-tailed deer detection rates at sites with coyotes were highest when presumed forage availability was relatively low. These findings suggest that white-tailed deer may be exhibiting an active avoidance behavioral response to predators by increasing movement rates when coyotes are present in an area, perhaps due to reactive evasive maneuvers and/or proactive attempts to reduce adverse encounters with them. Concurrently, coyotes could be occupying sites with higher white-tailed deer densities. Because white-tailed deer did not exhibit significant shifts in daily activity patterns based on coyote occupancy, we further suggest that white-tailed deer in our study system generally do not use temporal partitioning as their primary strategy for avoiding encounters with coyotes. Overall, our study implements a recently developed analytical approach for modeling multi-species occupancy from camera traps and provides novel ecological insight into the complex relationships between predator and prey species.

A PRELIMINARY INVESTIGATION OF PATHOGEN EXPOSURE OF ADULT FEMALE WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS) AND SURVIVAL OF ASSOCIATED FAWNS IN THE WESTERN DAKOTAS, USA

Exposure of a dam to pathogens may potentially affect her fawns positively or negatively. Mammalian females transfer immunologic protection to their offspring via colostrum obtained while nursing. Conversely, chronic diseases in dams may potentially result in small and weak neonates, reduced milk production or quality, or infection. Little is known about how pathogen exposure in adult female white-tailed deer (Odocoileus virginianus) affects offspring survival. Our objective was to assess pathogen exposure for female white-tailed deer and subsequent survival rates of fawns in Dunn and Grant counties, North Dakota, and Perkins County, South Dakota, USA. We collected blood serum from 150 adult female deer during 2014. We compared survival of 49 fawns to maternal exposure to 10 pathogens from 37 of 150 adult females. There was no difference in fawn mass between dams based on antibody status and no difference in fawn survival for nine pathogens. The 12-wk survival for fawns born to mothers with antibodies against bovine herpesvirus 1 (BoHV-1, causing infectious bovine rhinotracheitis) was lower than for fawns born from mothers without antibodies against BoHV-1; however, the indirect or direct impacts of BoHV-1 exposure in mothers on fawn survival are unclear. Although our findings suggest that the cost of exposure to previous diseases may have minimal impact on short-term fawn survival for most pathogens, additional research with increased sample sizes is needed to confirm our findings.

Birth date determines early calf survival in migratory caribou

The decline of most caribou (Rangifer tarandus) populations underlines the need to understand the determinants of key demographic parameters. In migratory caribou, we have limited information on rates and drivers of pre-weaning mortality. We fitted 60 pregnant females of the Rivière-aux-Feuilles caribou herd with GPS camera collars to track the survival of calves from birth to weaning in 2016-2018. Over the three years, calf survival rate before weaning, i.e. to 01-Sep, approximately three months of age, was 0.63 (CI 0.50-0.77). Summer mortality risk was mainly influenced by calf birth date, with calves born earlier in the calving season having a lower mortality risk than those born later. Mortality also increased when calves experienced low or high temperature during calving. This study provides the first estimates of pre-weaning survival of migratory caribou calves in this herd, illustrating the value of new technologies to collect data otherwise difficult to obtain in widely distributed migratory populations. This approach can easily be extended to other large herbivores and predators. Our study brings new insights on how climate change may affect summer juvenile survival given the increased temperatures and faster changes in plant phenology expected in the future.

Patterns of white-tailed deer movements in suburban Maryland: implications for zoonotic disease mitigation

Understanding the ecology of the often dense white-tailed deer populations in urban and suburban landscapes is important for mitigating a variety of conflicts that arise with dense human populations, such as issues surrounding zoonotic disease mitigation. We collared white-tailed deer in highly suburban areas of Howard County, Maryland with high-resolution GPS collars. Then, we created autocorrelated kernel density home ranges for broader land use analyses and concurrently used general additive models to characterize fine-scale hourly measures of speed, activity, and proximity to residential buildings. Suburban deer home ranges encompassed approximately 35% direct residential land, and an average of 71 and 129 residential properties were found within female and male core ranges, respectively. Sex, time of day, and day of year all influenced fine-scale speeds, activity levels, and proximity to residential property buildings. Deer moved into residential areas nightly, especially in winter, and exhibited bouts of increased speed and activity shortly after sunrise and sunset, with distinctive seasonal changes. We discuss how variation in home ranges and movements may influence population management success and explore year-round periods of increased risk of deer transporting ticks to residential areas. These findings focus our broad understanding of deer movements in suburban and urban landscapes to improve deer population management and to mitigate the spread of ticks into residential areas.

Capture method affects survival estimates and subsequent interpretation of ecological covariates for a long-lived cervid

Understanding what variables affect ungulate neonate survival is imperative to successful conservation and management of the species. Predation is commonly cited as a cause-specific source of mortality, and ecological covariates often influence neonate survival. However, variation in survival estimates related to capture methodology has been documented with opportunistically captured neonates generally displaying greater survival than those captured via aid of vaginal implant transmitters (VITs), likely because of increased left truncation observed in the opportunistically captured datasets. Our goal was to assess whether 3- and 6-month survival estimates varied by capture method while simultaneously assessing whether capture method affected model selection and interpretation of ecological covariates for white-tailed deer neonates captured from three study sites from 2014 to 2015 in North Dakota and South Dakota, USA. We found survival varied by capture method for 3-month neonate survival with opportunistically captured neonates displaying up to 26% greater survival than their counterparts captured via VITs; however, this relationship was not present for 6-month survival. We also found model selection and subsequent interpretation of ecological covariates varied when analyzing datasets comprised of neonates captured via VITs, neonates captured opportunistically, and all neonates combined regardless of capture method. When interpreting results from our VIT-only analysis for 3-month survival, we found survival varied by three time intervals and was lowest in the first two weeks of life. Capture method did not affect 6-month survival, which was most influenced by total precipitation occurring during 3 - 8 weeks of a neonate's life and percent canopy cover found at a neonate's capture site. Our results support previous research that capture method must be accounted for when deriving survival estimates for ungulate neonates as it can impact derived estimates and subsequent interpretation of results.