Using GPS collars to determine parturition and cause‐specific mortality of moose calves

Abstract

Global positioning system (GPS) collars have been deployed on adult moose (Alces americanus) and other ungulates to study various aspects of their ecology, but until the current study they have not been fitted to moose neonates. The moose population in northeastern Minnesota, USA, has been declining since 2006, and information on neonatal survival and cause‐specific mortality are needed. We monitored hourly movements of GPS‐collared females for indications of calving. During 2 May–2 June 2013 we observed 47 of 73 collared females (50 known pregnant, 17 not pregnant, 6 unknown pregnancy status) make “calving movements” followed by a clustering of locations. After allowing a mean bonding time of 40.2 hr, we approached their calving sites and captured and GPS‐collared 49 neonates from 31 dams. We closely monitored dam–calf movements and launched rapid investigative responses to calf mortality notifications to determine cause of mortality. Mean response time was 53.3 hr, but ranged from 0.3 hr to 579 hr, depending on collar accessibility and proper functioning of the GPS component. We censored capture‐related mortalities and slipped collars. Twenty‐five of 34 calves (74%) died of natural causes as of 31 December 2013, including 1 after natural abandonment, 1 after abandonment of unknown cause, 1 drowning, 1 unknown predator kill, 1 lethal infection from wolf (Canis lupus) bites, 4 black bear (Ursus americanus) kills, 12 wolf kills, and 4 “probable wolf kills.” As this technology develops, the quantity and quality of survival, cause‐specific mortality, movement, and habitat use data generated from intense monitoring of GPS‐collared adults and offspring will have unprecedented value associated with management at the population and landscape scales. © 2015 The Wildlife Society.

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

“…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 ). All captures and handling met American Society of Mammalogists guidelines (Sikes and the Animal Care and Use Committee of the American Society of Mammalogists ).…”

“…State and tribal moose harvests were suspended in 2013 because of the steady population decline, but a limited tribal harvest resumed in 2016 (DelGiudice , Edwards , Schrage ). Grey wolves and American black bears ( Ursus americanus ) preyed on moose calves (Lenarz et al ; Patterson et al ; Severud et al , b ); their densities were estimated at 4.4/100 km 2 and 23/100 km 2 , respectively (Garshelis and Noyce , Mech et al ). White‐tailed deer ( Odocoileus virginianus ), managed at pre‐fawning densities of <4/km 2 , were primary prey of wolves in the area (Nelson and Mech , DelGiudice et al , MNDNR ).…”

“…Wolves were harvested in this region during 2012–2014 (Stark and Erb ; D. Stark, MNDNR, personal communication), immediately prior to and during this study, but were federally relisted in December 2014. Upon den emergence, bears consumed succulent roots of aquatic grasses, flowers and catkins from a variety of tree and shrub species, and supplemented their diet with ungulate neonates and ants (family Formicidae) during May and June (Kunkel and Mech , Garshelis and Noyce , Severud et al ). Bear harvest during 2011–2016 in bear management unit 31 ranged from 197 to 363 bears (5‐yr mean = 289; Garshelis and Tri ).…”

White-tailed Deer (<i>Odocoileus virginianus</i>) Subsidize Gray Wolves (<i>Canis lupus</i>) During a Moose (<i>Alces americanus</i>) Decline: A Case of Apparent Competition?

“…To best determine the influence of wolf predation on Moose, radio-tagged adult and calf Moose should be studied for cause-specific mortality (Severud et al 2015). We recommend continued multi-faceted research (e.g., use of thermal refugia, habitat use with respect to deer, etc.)…”

“…Wolves were implicated in this decline based on an inverse relation between their numbers in the northeastern part of Moose range and the calf:cow ratio (the number of calves per cow observed during winter surveys; Mech and Fieberg 2014). Wolves may contribute to limiting Moose populations (Peterson et al 1984;Larsen et al 1989) by predation on calves (Testa et al 2000;Bertram and vivion 2002) and were a major source of calf mortality in northeastern Minnesota (Severud et al 2015). Following the decline in Moose, wolves could either decline or broaden their diet (increase consumption of an alternate prey) to include deer.…”