Winter as a nutritional bottleneck for North American porcupines (Erethizon dorsatum)

Abstract

North American porcupines are distributed across a wide variety of habitats where they consume many different species of plants. Winter is a nutritional bottleneck for northern populations, because porcupines remain active when environmental demands are high and food quality is low. We used captive porcupines to examine physiological responses to low-quality diets at high energy demands during winter at ambient temperatures as low as -39 degrees C. We did not observe an endogenous pattern of body mass gain or loss when porcupines were fed a low nitrogen diet (1.1% dry matter) ad libitum through winter. Dry matter intake declined from 43.6 to 14.6 g kg(-0.75) d(-1) even though ambient temperatures declined from -3 to -30 degrees C, which indicates a seasonal decrease in metabolic rate. Porcupines consuming white spruce needles maintained digestive efficiency for energy (61%) and neutral detergent fiber (NDF) (50%). However, low requirements for energy (398 kJ kg(-0.75) d(-1)) and nitrogen (209 mg kg(-0.75) d(-1)) minimized the loss of body mass when intakes were low and plant toxins increased urinary losses of energy and nitrogen. Porcupines were also able to tolerate low intakes of sodium, even when dietary potassium loads were high. Porcupines use a flexible strategy to survive winter: low requirements are combined with a high tolerance for dietary imbalances that minimize the use of body stores when demands exceed supply. However, body stores are rapidly restored when conditions allow. Porcupines posses many physiological abilities similar to specialist herbivores, but retain the ability of a generalist to survive extreme conditions by using a variety of foods.

Beton‐ und Stahlbetonbau aktuell 7/2016

“…Den use was infrequent in our study area and did not appear to be related to porcupine size or ambient temperature. However, Alaskan porcupines may be less dependent on dens than smaller porcupines from more temperate regions because LCT may be colder in Alaskan animals (DeMatteo and Harlow 1997, Coltrane and Barboza 2010), and because potential den sites may be less abundant or less accessible in Alaska (Roze 1987, 2009; Morin et al 2005). As a result, white spruce trees may provide refugia for Alaskan porcupines that is similar to the thermal refugia provided by dens for porcupines in other locations.…”

“…Survival of northern porcupine populations may ultimately rely on winter habitat availability and selection. During long Alaskan winters, porcupines endure low ambient temperatures while subsisting on poor quality foods that are high in plant secondary metabolites and fiber and low in nutrients and energy (Coltrane and Barboza 2010). Habitat selection in Alaskan porcupines in winter is therefore a tradeoff between nutritional and thermoregulatory challenges, as well as predation risks.…”

“…As a result, free‐ranging porcupines lose up to 34% of total body mass at an average rate of 17 ± 6 g/day over an Alaskan winter (Coltrane et al 2011). Captive porcupines fed a diet of white spruce ( Picea glauca ) needles lost body mass at 49 ± 19 g/day (Coltrane and Barboza 2010), a loss rate that could not be sustained throughout the winter. However, porcupines can readily regain body mass by consuming higher quality forage when available (Coltrane and Barboza 2010).…”

“…Captive porcupines fed a diet of white spruce ( Picea glauca ) needles lost body mass at 49 ± 19 g/day (Coltrane and Barboza 2010), a loss rate that could not be sustained throughout the winter. However, porcupines can readily regain body mass by consuming higher quality forage when available (Coltrane and Barboza 2010). As a result, we suspect that porcupines select habitats that allow for the ability to switch between several food items, such as coniferous to deciduous trees, when toxin loads or energy loss exceed an internal threshold (Wiggins et al 2006).…”

Effects of grazing on the northern three‐toed jerboa pre‐ and post‐hibernation

“…Food availability changes seasonally with seasonal plant growth in northern temperate regions, with winter often considered to be a bottleneck for non‐hibernators because of food shortage and harsh environmental conditions, especially at high northern latitudes (Solonen , Coltrane and Barboza ). Animals have evolved a variety of ways to adapt to this predictable food shortage, such as winter food caching and hibernation (Geiser and Ruf , Turbill et al ).…”