Moose calf mortality project

Purpose

A collared moose calf

The DNR's management challenge is to increase the number of newborn moose calves that survive to become productive adult females.

Examining the reproductive success of moose is essential to understanding changes in population size over time. That is why, in 2013, the DNR launched an important study of reproductive success of northeastern Minnesota's declining moose population.

Generally, this study has been focused on:

  • Assessing fertility (yearly pregnancy rates) of adult females;
  • Total calf production;
  • Age-specific survival from birth (when calves are most vulnerable);
  • Deaths by various causes;
  • How many moose calves survive to one year (recruitment), which is when the probability of survival increases dramatically compared to young calves and old adults; and
  • Assessments of habitat used by moose for birthing and rearing calves.

To accomplish these objectives, scientists fitted newborn calves with cutting-edge global positioning system (GPS) collars for the very first time worldwide. Having their mothers also fitted with GPS collars, and both collecting locations every hour synchronously for the first two years of the study, allowed researchers to learn so much about maternal movement behavior and patterns relative to their calves, that they were able to continue collecting valuable data for an additional two years without collars being fitted to newborn calves.

While field data collection ended in spring 2017, analyses continue. To date, that work has yielded critical information published in 10 peer-reviewed journal articles.

Publications

Severud, W. J., T. R. Obermoller, G. D. DelGiudice, and J. R. Fieberg. 2019. Survival and cause-specific mortality of calves in northeastern Minnesota's declining moose population. Journal of Wildlife Management. In press.

Obermoller, T. R., G. D. DelGiudice, and W. J. Severud. 2019. Maternal behavior indicates survival and cause-specific mortality of moose calves. Journal of Wildlife Management.

Severud, W. J., G. D. DelGiudice, and T. R. Obermoller. 2019. Association of moose parturition and post-parturition habitat with calf survival. Journal of Wildlife Management 83: 175-183.

Obermoller, T. R., G. D. DelGiudice, and W. J. Severud. 2018. Assessing expandable GPS collars for moose neonates. Wildlife Society Bulletin 42: 314-320; DOI: 10.1002/wsb.878.

DelGiudice, G. D., W. J. Severud, T. R. Obermoller, and V. St-Louis. 2018. Gaining a deeper understanding of capture-induced abandonment of moose neonates. Journal of Wildlife Management 82: 287-298

DelGiudice, G. D., and W. J. Severud. 2016. Blood profiles and associated birth characteristics of free-ranging moose (Alces americanus) neonates in a declining population in northeastern Minnesota. Alces 52:85-99.

Severud, W. J., G. D. DelGiudice, and T. R. Obermoller. 2016. Minimizing mortality of moose neonates from capture-induced abandonment. Alces 52:73-83.

Severud, W. J., and G. D. DelGiudice. 2015. Potential vertical transmission of winter ticks (Dermacentor albipictus) from moose (Alces americanus) dams to neonates. Journal of Wildlife Diseases 52:186-188.

Severud, W. J., G. D. DelGiudice, T. R. Obermoller, T. A. Enright, R. G. Wright, and J. D. Forester. 2015. Using GPS collars to determine parturition and cause-specific mortality of moose calves. Wildlife Society Bulletin 39: 616-625.

DelGiudice, G. D., W. J. Severud, T. R. Obermoller, R. G. Wright, T. A. Enright, and V. St-Louis. 2015. Monitoring movement behavior enhances recognition and understanding of capture-induced abandonment of moose neonates. Journal of Mammalogy 96: 1005-1016.

Highlights of our findings

Information collected as part of this study is essential to a management understanding that may help stabilize or reverse Minnesota's declining moose population. Click on the topics below for more details on the study's methods and findings.

Fertility
During the four-year study, fertility of adult females was robust, reflected by an average pregnancy rate of 83 percent, which is indicative of good nutritional body condition of most adult females entering the fall breeding season.
Calf production
Average calf production during our study (1,603 calves) was 58 percent lower compared to average calf production during 2006 to 2009 (3,789 calves), just before the moose population sharply declined (2009 to 2012). This was due primarily to the notably lower number of adult females on the landscape in northeastern Minnesota that could get pregnant.
Calf survival
  • Recruitment of calves, survival to one year of age, was low throughout the study.
  • During 2013−14 and 2014−15 (data pooled), survival of calves to 9 months of age (near recruitment), monitored by GPS collars of the calves and mothers, and fall and late winter helicopter surveys, was 0.34 (95% confidence interval = 0.23 to 0.52).
  • During 2015−16 and 2016−17 (data pooled), calf survival to 9 months of age, monitored by GPS collars of adult females, their “calving and mortality movements,” and by fall and late winter helicopter surveys, was 0.35 (95% confidence interval = 0.26 to 0.48).
  • Thirty-five to 42 percent of total mortality occurred within 30 days of birth.
  • Calving sites afforded relatively safe habitat for the newborns; predator-kills occurred an average 32 days after the mother and her calf or calves departed from the calving site and an average distance of 1,553 meters from the calving site.
Causes of mortality
  • Predation was consistently the leading cause of calf mortality during the study.
  • During 2013−14 and 2014−15, wolf and black bear predation accounted for 65 percent and 16 percent of calf mortality, respectively.
  • During 2015−16 and 2016−17, 69 percent and 15 percent of the calf mortality was attributable to wolves and bears.
Calving habitat
  • Habitat use during calving and the immediate post-parturition period, when newborns are particularly vulnerable to various mortality forces, can have a notable influence on recruitment and population performance.
  • We compared characteristics of habitat used during pre-calving, calving, peak-lactation (about 21 days after birth), and at mortality sites.
  • Generally, adult females moved to areas of more conifer cover for calving, but during peak lactation mothers and their calves used areas that were steeper, afforded abundant forage and high concealment, but less conifer cover.
  • Calf mortalities tended to occur at sites that were more level than other locations used by mothers and their young, which may have limited their capacity for vigilance.
  • Our study also suggests that calving sites characterized by more deciduous forest, rather than forested wetland, may be key to successful rearing of calves to recruitment.
  • To support future calving success, key considerations for habitat improvement should include nutritional requirements and arrangement of forage relative to cover and slope.
Additional important findings
  • This study has also included detailed controlled testing and field evaluation of the first GPS collars fitted to newborn moose calves. Derived information will contribute to their further development and improved performance in the future.
  • Capture-induced abandonment of newborn ungulate (hoofed animals) calves has been a notable challenge to field research efforts worldwide for decades, which has limited progress of our understanding of demographics of populations and our ability to effectively manage them. The limited performance of technology has been a critical factor hindering advancement of our knowledge and understanding of the critical life stage of moose, from birth to recruitment (survival to one year).
  • Fitting both adult female moose and their newborns with GPS collars facilitated collection and close examination of location and movement data that facilitated a much better understanding of capture-induced abandonment.
  • Subsequently, this allowed us to characterize abandonment in a way that permits confident early recognition when it occurs and effective calf recovery. Importantly, it also helped us to markedly minimize its occurrence by modifying our capture and handling approach.
  • Just as veterinarians assess the health and well-being of domestic animals by way of examination of blood profiles, the same approach has been applied to wild animals, such as moose. Analyses of blood characteristics of newborns may be particularly important given their high probability of death.
  • We have begun establishing reference values for 15 hematological and 24 serum characteristics, including metabolites, chemistries, electrolytes, enzymes, and metabolic and stress hormones, to help in the assessment of newborn health far beyond what is possible by physical examination alone.
  • Finally, using the advantages and insights afforded by GPS-collared newborns and their mothers, our study has firmly documented the utility of using movement behavior (“calving movement”) to determine which, when, and where adult females are calving, as well as, when and where a calf of a GPS-collared mother is killed by various mortality causes, particularly with respect to predation by wolves.
  • This understanding of movement behavior will be very advantageous when GPS-collaring of newborns is not part of study protocols for any of a variety of reasons.

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