Timing and causes of mortality in the endangered Vancouver Island marmot (Marmota vancouverensis)

Abstract

We used radiotelemetry to evaluate seasonal survival rates and mortality factors for a critically endangered island endemic, the Vancouver Island marmot (Marmota vancouverensis Swarth, 1911). Recovery of radio transmitters and marmot remains suggested that predation was the major cause of mortality, accounting for at least 24 of 29 (83%) known-fate deaths recorded since radiotelemetry efforts began in 1992. Wolves (Canis lupus L., 1758) and cougars (Puma concolor (L., 1771)) apparently accounted for 17 deaths (59%). Three marmots (10%) were killed by golden eagles (Aquila chrysaetos (L., 1758)), four (14%) were killed by unknown predators that probably included all of the above species, two (7%) died from unknown causes, and three (10%) died during hibernation in a single burrow. Mortality rates varied seasonally. The daily probability of death during hibernation was very low (P death = 0.016). The probability of death was also low from spring emergence through 31 July (P death = 0.051), but was eight times higher in August (P death = 0.395) and four times higher in September (P death = 0.175). We concluded that predation was the proximate cause of recent declines in wild Vancouver Island marmot populations, that losses were highly concentrated in late summer, and that previous studies exaggerated the importance of winter mortality. We suggest that high predation rates were associated with forestry and altered predator abundance and hunting patterns.Résumé : La radio-télémétrie nous a servi à évaluer le taux saisonnier de survie et les facteurs de mortalité chez la marmotte de l'île de Vancouver (Marmota vancouverensis Swarth, 1911), une espèce endémique insulaire fortement menacée. La récupération des émetteurs et des carcasses de marmottes laisse croire que la prédation est la cause principale de mortalité, représentant au moins 24 (83 %) des 29 cas étudiés depuis le début de l'utilisation de la radio-télé-métrie en 1992. Les loups (Canis lupus L., 1758) et les couguars (Puma concolor (L., 1771)) sont apparemment responsables de 17 (59 %) des morts. Trois (10 %) des marmottes ont été tuées par des aigles royaux (Aquila chrysaetos (L., 1758)) et quatre (14 %) par des prédateurs inconnus qui incluent peut-être toutes les espèces mentionnées pré-cédemment; deux (7 %) sont mortes de causes inconnues et trois (10 %) sont mortes dans un même terrier durant l'hibernation. Les taux de mortalité varient en fonction de la saison. La probabilité quotidienne de mortalité durant l'hibernation est très faible (P mort = 0,016). La probabilité de mortalité est aussi faible de l'émergence printanière jusqu'au 31 juillet (P mort = 0,051), mais elle est huit fois plus élevée en août (P mort = 0,395) et quatre fois plus élevée en septembre (P mort = 0,175). En conclusion, la prédation est la cause immédiate des déclins récents des populations sauvages de marmottes de l'île de Vancouver, les pertes sont fortement concentrées en fin d'été et les études antérieures ont exagéré l'importance de la mortalité hivernale. Nous croyons que ...

Stranded on an island: consequences of forest fragmentation for body size variations in an arboreal mammal, the edible dormouse (Glis glis)

“…Both body size and trophic level of a species determine the relative extent to which population dynamics are shaped by predation pressure or resource availability. In small herbivores, and especially in rodents, predation pressure is thought to be the main factor determining mortality rate and therefore population dynamics (Norrdahl and Korpimäki 1995;Ims and Andreassen 2000;Palkovacs 2003;Bryant and Page 2005;McCleery et al 2008). We assumed that predation also primarily determined survival rates in edible dormice, because mortality was shown to be lowest when dormice remained well protected from predators within their hibernacula during periods of hypothermia (Ruf et al 2006;Bieber and Ruf 2009;Lebl et al 2011).…”

Patterns of within and between-colony microsatellite variation in the endangered Vancouver Island marmot (Marmota vancouverensis): implications for conservation

“…Based on ear-tagged animals, Bryant (1998) recorded dispersal movements of 1-11 km, but numerous records of solitary marmots in new habitats suggest dispersal movements [25 km (Bryant and Janz 1996). More recently, radiotagged marmots have been observed to make movements of 10-30 km within periods of a few days or weeks (Bryant and Page 2005). Forests, clearcuts, rivers and roads do not appear to represent physical barriers to dispersal, although logging of high elevation forests may alter dispersal patterns through creation of new and nearby habitat (Bryant 1996).…”

“…These new habitats proved to be unstable due to natural reforestation. Thus, populations did not survive over longer periods and most colonies declined sharply after 1994 (Bryant 2000). Annual population counts suggest that in the mid-1980s the Vancouver Island marmot population consisted of 300-350 individuals, declining to fewer than 100 in 1998 (Bryant 1998) and fewer than 35 individuals by 2003 (Bryant and Page 2005).…”

“…Thus, populations did not survive over longer periods and most colonies declined sharply after 1994 (Bryant 2000). Annual population counts suggest that in the mid-1980s the Vancouver Island marmot population consisted of 300-350 individuals, declining to fewer than 100 in 1998 (Bryant 1998) and fewer than 35 individuals by 2003 (Bryant and Page 2005). In addition to losses of habitat due to natural forest regeneration, marmot populations in both natural and clearcut habitats also suffered increasing levels of predation (Bryant and Page 2005) from wolves (Canis lupus), cougars (Puma concolor) and golden eagles (Aquila chrysaetos).…”

Impacts of industrial developments on the distribution and movement ecology of wolves (Canis lupus) and woodland caribou (Rangifer tarandus caribou) in the South Peace region of British Columbia.

“…Also, past studies that have considered wolf interactions with industrial development have considered only a few disturbance types, but not the cumulative effects of multiple types (but see Lesmerises et al 2012 habitat ecology serve as a foundation for increasing our knowledge o f the spatial and temporal relationships of these two species. Such insights may also apply to other species influenced by increasing human disturbances and apparent competition (Robinson et al 2002, Kristan and Boarman 2003, Baldi et al 2004, Bryant and Page 2005, Gibson et al 2006. Understanding the spatial complexities of co-occurring populations can aid in conservation planning for the long-term persistence of threatened species.…”