Cause‐specific neonatal mortality of white‐tailed deer in Wisconsin, USA

Abstract

Species' population dynamics are tied to neonatal survival. White-tailed deer (Odocoileus virginianus) fawn survival varies according to spatially explicit patterns of natural (e.g., starvation, predation) and human-caused mortalities (e.g., vehicle collision). Our objective was to compare fawn survival under different, though representative, ecological conditions in Wisconsin USA. We identified 2 ecologically distinct study areas: the northern forest (NF) and the eastern farmland (EF). Beginning in May (2011-2013), we fitted fawns in both areas with radio-collars and tracked their survival daily until 31 August of the capture year. We obtained daily weather data for each study area to model weather effects on survival. We captured 89 (NF), and 139 (EF) fawns, and observed 42 (NF) and 43 (EF) mortalities. Predation mortality was higher than other mortality causes in the NF, and mortality due to natural causes other than predation was higher for fawns in the EF. Female fawns had higher survival than males, and fawns in 2011 in the NF had lower survival than fawns in 2012 or 2013. During the first 40 days of life, occurrence of precipitation associated with a threefold increase in daily hazard of death in the EF, but effects of daily low temperatures were trivial. In the NF, precipitation had little effect, but a decrease in daily low temperature by 0.568C increased the daily hazard of mortality by 5%. Because risks facing fawns vary with ecological context, understanding specific factors that affect fawn survival is important for predicting local outcomes of white-tailed deer management.

Landscape‐level patterns in fawn survival across North America

“…Overall fawn survival was positively associated with agricultural land cover, which supports hypotheses of a higher nutritional plane potential in agricultural landscapes benefiting lactating females (Hewitt , Warbington et al ). White‐tailed deer population declines have been described in landscapes where agricultural land cover exceeds 75%, but we did not observe lesser fawn survival in Grovenburg et al (, ) where the study area's agricultural land cover exceeded 75% in comparison to other studies in the meta‐analysis where agricultural land cover did not exceed this threshold (Hewitt ).…”

“…; see Table S1, available online in Supporting Information). The current field study, Vreeland et al (), and Warbington et al () described their 2 study areas in enough detail to treat each study area as a separate population.…”

Landscape‐scale habitat characteristics and neonatal white‐tailed deer survival

“…The high availability of these crops, combined with a relatively low deer density during the study (~7 deer/km 2 ; K. H. Wiskirchen, Missouri Department of Conservation, personal communication), and similar birth masses to comparable regions (2.56–2.81 kg in South Dakota, USA [Grovenburg et al ], 2.47–4.16 kg in northern Michigan, USA [Duquette et al ]) makes it unlikely that neonate survival was low in the GP because of nutritional constraints. Unfavorable spring and summer weather conditions can also lead to a decline in neonate survival rates (Gilbert and Raedeke , Warbington et al , Michel et al ); however, we did not observe abnormally cold or wet weather during our study. Further, we did not observe higher incidences of natural‐caused mortality, such as disease or abandonment.…”

Landscape influence on dispersal of yearling male white‐tailed deer

“…This landscape mostly (80%) consisted of forested habitats, including maple ( Acer spp. ), aspen ( Populus tremuloides ), balsam fir ( Abies balsamea ), white pine ( Pinus strobus ), alder ( Alnus rugosa ), and black spruce ( Picea mariana ; Warbington et al ). The region had a rich predator guild where black bears ( Urus americanus ) and bobcats ( Lynx rufus ) were classified as common, numerous gray wolf packs existed, and coyotes ( Canis latrans ) were widespread (MacFarland et al , Rolley et al , Wydeven et al ).…”

“…Ownership was primarily private land (97%), and row‐crop agriculture was the principal land use. Forests were extensively fragmented (35% forest cover) by agricultural fields, with much of the forests reduced to isolated woodlots of sugar maple ( A. saccarum ), American basswood ( Tilia americana ), aspen, birch ( Betula papyrifera ), northern white cedar ( Thuja occidentalis ), balsam fir, and tamarack ( Larix laricina ; Warbington et al ). Black bears, bobcats, and wolves were infrequent, but coyotes were reportedly common (MacFarland et al , Rolley et al ).…”