Compensatory mortality in a recovering top carnivore: wolves in Wisconsin, USA (1979–2013)
Populations of large terrestrial carnivores are in various stages of recovery worldwide and the question of whether there is compensation in mortality sources is relevant to conservation. Here, we show variation in Wisconsin wolf survival from 1979 to 2013 by jointly estimating the hazard of wolves’ radio-telemetry ending (endpoint) and endpoint cause. In previous analyses, wolves lost to radio-telemetry follow-up (collar loss) were censored from analysis, thereby assuming collar loss was unconfounded with mortality. Our approach allowed us to explicitly estimate hazard due to collar loss and did not require censoring these records from analysis. We found mean annual survival was 76% and mean annual causes of mortality were illegal killing (9.4%), natural and unknown causes (9.5%), and other human-caused mortality such as hunting, vehicle collisions and lethal control (5.1%). Illegal killing and natural mortality were highest during winter, causing wolf survival to decrease relative to summer. Mortality was highest during early recovery and lowest during a period of sustained population growth. Wolves again experienced higher risk of human-caused mortality relative to natural mortality as wolves expanded into areas with more human activity. We detected partial compensation in human- and natural-caused mortality since 2004 as the population saturated more available habitat. Prior to 2004, we detected additivity in mortality sources. Assessments of wolf survival and cause of mortality rates and the finding of partial compensation in mortality sources will inform wolf conservation and management efforts by identifying sources and sinks, finding areas of conservation need, and assessing management zone delineation.
KeywordsAdditive mortality Canis lupus Cause-specific mortality Censoring Survival
We thank D. Heisey, R. Jurewitz, D. MacFarland, N. Roberts, R. Schultz, D. Thiel and J. Weidenhoeft for their development of the wolf monitoring program in Wisconsin, on-going data collection, and feedback on this research. Thank you to other Wisconsin Department of Natural Resources staff and volunteers who contributed to wolf monitoring and to the Department of Forest and Wildlife Ecology, UW-Madison for their support. We thank G. Péron for a very helpful review of this manuscript. Thank you to our additional sources of funding and support.
Author contribution statement
All authors conceived ideas and designed methodology; AW collected and curated data; JS and TVD analyzed data; JS led writing of the manuscript. All authors contributed critically to drafts and gave final approval for publication.
This study was funded by National Science Foundation-IGERT (Grant Number DGE-1144752), the Wisconsin Department of Natural Resources, the University of Wisconsin-Madison Department of Forest and Wildlife Ecology, and a USDA Hatch Act Grant.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Anderson DR, Burnham KP (1976) Population ecology of the mallard: VI. The effect of exploitation on survival, vol. 128. US Fish and Wildlife Service Resource Publication, pp 1–66Google Scholar
- Fuller T (1989) Population dynamics of wolves in north-central Minnesota. Wildl Monogr 105:1–41Google Scholar
- Fuller TK, Mech LD, Cochrane JF (2003) Wolf population dynamics. In: Mech LD, Boitani L (eds) Wolves: behavior, ecology, and conservation. The University of Chicago Press, Chicago, pp 161–191Google Scholar
- Klein JP, Moeschberger ML (2003) Survival analysis: statistical methods for censored and truncated data. Springer, New YorkGoogle Scholar
- MacFarland D, Wiedenhoeft JE (2013) Wisconsin gray wolf post-delisting monitoring: 27 January 2012 through 14 April 2013. Bureau of Wildlife Management, Wisconsin Department of Natural Resources, Madison, WisconsinGoogle Scholar
- Mladenoff DJ, Clayton MK, Pratt SD, Sickley TA, Wydeven AP (2009) Change in occupied wolf habitat in the northern Great Lakes region. In: Wydeven AP, Van Deelen TR, Heske EJ (eds) Recovery of Gray wolves in the Great Lakes region of the United States: an endangered species success story. Springer, New York, pp 119–138CrossRefGoogle Scholar
- Nychka D, Furrer R, Sain S (2015) Fields: Tools for spatial data., R package version 8.2-1. http://CRAN.R-project.org/package=fields edn
- Plummer M (2003) JAGS: a program for analysis of Bayesian graphical models using Gibbs sampling. In: Hornik K, Leisch F, Zeileis A (eds) Proceedings of the 3rd international workshop on distributed statistical computing, vol. 124. Technische Universit at Wien, Vienna, Austria, pp 1–10Google Scholar
- Plummer M (2011) rjags: Bayesian graphical models using MCMC. R package version 3-5Google Scholar
- Prentice RL, Gloeckler LA (1978) Regression analysis of grouped survival data with application to breast cancer data. Biometrics:57-67Google Scholar
- R developement Core Team (2013) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, AustriaGoogle Scholar
- Schaub M, Lebreton JD (2004) Testing the additive versus the compensatory hypothesis of mortality from ring recovery data using a random effects model. Anim Biodivers Conserv 27:73–85Google Scholar
- Sinclair ARE, Pech RP (1996) Density dependence, stochasticity, compensation and predator regulation. Oikos:164–173Google Scholar
- Van Deelen TR (2009) Growth characteristics of a recovering wolf population in the Great Lakes region. In: Wydeven AP, Van Deelen TR, Heske EJ (eds) Recovery of gray wolves in the great lakes region of the United States: an endangered species success story. Springer, New York, pp 139–153CrossRefGoogle Scholar
- Wydeven AP, Schultz RN, Thiel RP (1995) Monitoring of a recovering gray wolf population in Wisconsin, 1979-1991. In: Carbyn LN, Fritts SH, Seip DR (eds) Ecology and Conservation of Wolves in a Changing World. Canadian Circumpolar Institute, Edmonton, pp 147–156Google Scholar
- Wydeven AP, Wiedenhoeft JE, Schultz RN, Bruner J, Boles S (2012) Wisconsin endangered resources report#143: Status of the timber wolf in Wisconsin. Performance report 1 July 2011 through 30 June 2012 (also progress reports for 15 April 2011 - 14 April 2012, and 2011 summaries). Bureau of Endangered Resources, Wisconsin Department of Natural Resources, Madison, WisconsinGoogle Scholar