Survival and cause‐specific mortality of moose calves in Northeastern Minnesota

Abstract

Ungulate reproductive success (calf production and survival) influences population performance. The moose (Alces alces) population in northeastern Minnesota, USA, has declined 65% from 2006 to 2018 but has begun to stabilize. Because causes of this decline were largely unknown, we investigated production, survival, and cause‐specific mortality of calves of the global positioning system (GPS)‐collared females in this population. In 2013 and 2014, we GPS‐collared 74 neonates and monitored them for survival. In 2015 and 2016, we monitored 50 and 35 calving females for signs of neonatal mortality using changes in adult female velocities and assessed seasonal calf survival by aerial surveys. In 2013 and 2014 (pooled), survival to 9 months was 0.34 (95% CI = 0.23–0.52) for collared calves, and in 2015 and 2016 (pooled) survival was 0.35 (95% CI = 0.26–0.48) for uncollared calves. Mortality in all 4 years was high during the first 50 days of life. In 2013 and 2014 (pooled), calving sites were relatively safe for collared neonates; predator‐kills occurred a median 17.0 days after departure and a median 1,142 m from calving sites. Predation was the leading cause of death of collared calves (84% of mortalities), with wolves (Canis lupus) accounting for 77% of these. Other forms of mortality for collared and uncollared calves included drowning, infection, vehicle collision, and natural abandonment. We documented higher wolf predation than other recent studies with similar predator communities. Identifying specific causes of calf mortality and understanding their relations to various landscape characteristics and other extrinsic factors should yield insight into mechanisms contributing to the declining moose population in northeastern Minnesota and serve as a basis for ecologically sound management responses. © 2019 The Wildlife Society.

Association of moose parturition and post‐parturition habitat with calf survival

“…Adult female moose use a variety of cover types for calving, often in proportion to their availability (Addison et al , Bowyer et al , Poole et al , McLaren et al ), yet some studies have reported selection for specific cover types used in post‐parturition areas, such as lowland conifer, shrublands, and regenerating forest (McGraw et al , McLaren et al ). Recently (2013–2015) in northeastern Minnesota, USA, few calf mortalities were observed at calving sites (Severud et al ), similar to observations elsewhere (Bubenik ). Moose and elk ( Cervus canadensis ) may use anthropogenic features as shields against predators, calving near roads or campsites that predators often avoid (Edwards , Lehman et al ).…”

“…Median age of calves at capture was 2 days (range = 1–5 days). We monitored 155 females (50 in 2013, 56 in 2014, and 49 in 2015) and 139 calves (49 collared in 2013 and 25 collared in 2014, approximately 65 uncollared calves were remotely monitored in 2015 via their mother's movements; Severud et al ). Details of moose capture and collar specifics were described elsewhere (Butler et al ; Carstensen et al , ; Severud et al ; Obermoller et al ).…”

“…Pregnant moose often moved long distances and subsequently localized to give birth (i.e., calving movement); we used this movement to locate neonates for collaring and to identify calving sites (Severud et al ). Females fitted with GPS collars also have been observed making repeated movements away from and return‐trips to focal areas where calves have been preyed upon (mortality movement); we used this movement to target mortality investigations of uncollared calves of collared females (Severud et al , Obermoller et al ).…”

“…We used starting and ending points of calving movements to identify pre‐calving and calving sites, respectively (Severud et al ). In 2015, we similarly surveyed locations where calf mortalities were confirmed by site evidence (e.g., bone fragments, hooves, hair, predator sign) following a mortality movement of the female, because neonates were not collared (Severud et al , Obermoller et al ). We recorded mortalities occurring at the birth‐site as both calving and mortality sites.…”

“…Northeastern Minnesota's moose population declined an estimated 65% from 2006 to 2018 (DelGiudice ), during which time estimated annual calf survival was 0.28–0.40 (Lenarz et al , Severud et al ). Patterns of calving and post‐parturition habitat use and their association with neonatal survival are largely unknown.…”