title: Re-evaluating neonatal-age models for ungulates: does model choice affect survival estimates?
abstract: New-hoof growth is regarded as the most reliable metric for predicting age of newborn ungulates, but variation in estimated age among hoof-growth equations that have been developed may affect estimates of survival in staggered-entry models. We used known-age newborns to evaluate variation in age estimates among existing hoof-growth equations and to determine the consequences of that variation on survival estimates. During 2001-2009, we captured and radiocollared 174 newborn (≤24-hrs old) ungulates: 76 white-tailed deer (Odocoileus virginianus) in Minnesota and South Dakota, 61 mule deer (O. hemionus) in California, and 37 pronghorn (Antilocapra americana) in South Dakota. Estimated age of known-age newborns differed among hoof-growth models and varied by >15 days for white-tailed deer, >20 days for mule deer, and >10 days for pronghorn. Accuracy (i.e., the proportion of neonates assigned to the correct age) in aging newborns using published equations ranged from 0.0% to 39.4% in white-tailed deer, 0.0% to 3.3% in mule deer, and was 0.0% for pronghorns. Results of survival modeling indicated that variability in estimates of age-at-capture affected short-term estimates of survival (i.e., 30 days) for white-tailed deer and mule deer, and survival estimates over a longer time frame (i.e., 120 days) for mule deer. Conversely, survival estimates for pronghorn were not affected by estimates of age. Our analyses indicate that modeling survival in daily intervals is too fine a temporal scale when age-at-capture is unknown given the potential inaccuracies among equations used to estimate age of neonates. Instead, weekly survival intervals are more appropriate because most models accurately predicted ages within 1 week of the known age. Variation among results of neonatal-age models on short- and long-term estimates of survival for known-age young emphasizes the importance of selecting an appropriate hoof-growth equation and appropriately defining intervals (i.e., weekly versus daily) for estimating survival.
authors.affiliation: Department of Natural Resource Management, South Dakota State University, Brookings, South Dakota, United States of America.
authors.forename: Troy W
authors.initials: TW
authors.lastname: Grovenburg
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, United States of America.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Monteith
authors.affiliation: Department of Biological Sciences, Western Illinois University, Macomb, Illinois, United States of America.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Jacques
authors.affiliation: U.S. Geological Survey, Iowa Cooperative Fish and Wildlife Research Unit, Department of Natural Resource Ecology and Management, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Klaver
authors.affiliation: Department of Forestry and Environmental Resources, Fisheries, Wildlife, and Conservation Biology, North Carolina State University, Raleigh, North Carolina, United States of America.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: DePerno
authors.affiliation: Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Brinkman
authors.affiliation: Department of Natural Resource Management, South Dakota State University, Brookings, South Dakota, United States of America.
authors.forename: Kyle B
authors.initials: KB
authors.lastname: Monteith
authors.affiliation: Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Sophie L
authors.initials: SL
authors.lastname: Gilbert
authors.affiliation: Department of Natural Resource Management, South Dakota State University, Brookings, South Dakota, United States of America.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Smith
authors.affiliation: Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Game, Bishop, California, United States of America.
authors.forename: Vernon C
authors.initials: VC
authors.lastname: Bleich
authors.affiliation: U.S. Fish and Wildlife Service, Kulm, North Dakota, United States of America.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Swanson
authors.affiliation: Department of Natural Resource Management, South Dakota State University, Brookings, South Dakota, United States of America.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Jenks
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002755:Choice Behavior; D003670:Deer / Q000254:growth & development*; D005260:Female; D005843:Geography; D008954:Models, Biological; D016019:Survival Analysis; D014481:United States