Investigating the mechanism for maintaining eucalcemia despite immobility and anuria in the hibernating American black bear (Ursus americanus)

Ursine hibernation uniquely combines prolonged skeletal unloading, anuria, pregnancy, lactation, protein recycling, and lipolysis. This study presents a radiographic and biochemical picture of bone metabolism in free-ranging, female American black bears (Ursus americanus) that were active (spring bears and autumn bears) or hibernating (hibernating bears). Hibernating bears included lactating and non-lactating individuals. We measured serum calcium, albumin, inorganic phosphate, creatinine, bone specific alkaline phosphatase (BSALP), CTX, parathyroid hormone, insulin-like growth factor-I (IGF-l), leptin, 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D] and sclerostin from 35 to 50 tranquilized hibernating bears and 14 to 35 tranquilized spring bears. We compared metacarpal cortical indices (MCI), measured by digital X-ray radiogrammetry, from 60 hunter-killed autumn bears and 79 tranquilized, hibernating bears. MCI was greater in autumn than winter in younger bears, but showed no seasonal difference in older bears. During hibernation eucalcemia was maintained, BSALP was suppressed, and CTX was in the range expected for anuria. During hibernation 1,25(OH)(2)D was produced despite anuria. 1,25(OH)(2)D and IGF-I were less in hibernating than spring bears. In a quarter of hibernating bears, sclerostin was elevated. Leptin was greater in hibernating than spring bears. In hibernating bears, leptin correlated positively with BSALP in non-lactating bears and with CTX in lactating bears. Taken together the biochemical and radiographic findings indicate that during hibernation, bone turnover was persistent, balanced, and suppressed; bone resorption was lower than expected for an unloaded skeleton; and there was no unloading-induced bone loss. The skeleton appears to perceive that it was loaded when it was actually unloaded during hibernation. However, at the level of sclerostin, the skeleton recognized that it was unloaded. During hibernation leptin appeared anabolic in non-lactating bears and catabolic in lactating bears. We hypothesize that ursine hibernation may represent a natural model in which suppression of the sympathetic nervous system prevents unloading-induced bone loss by influencing leptin's skeletal effects and preventing transmission of loading information.

Patch occupancy and dispersal of spruce grouse on the edge of its range in Maine

We surveyed 18 habitat patches (black spruce (Picea marinana) – tamarack (Larix larcina) wetlands) for spruce grouse (Dendragapus canadensis canadensis) on Mount Desert Island, Maine, during April–May in 1992 and 1993 to determine patch occupancy relative to patch area. We also equipped nine juvenile grouse with radio transmitters to determine movement and habitat use outside of patches during autumn dispersal. The 2 large patches (77 and 269 ha), 5 of 6 medium-sized (11–26 ha) patches and 1 of 10 small (4–8 ha) patches were occupied. Spruce grouse occupied smaller habitat patches than previously reported and occupied patches were closer (P < 0.05) to the nearest occupied patch ([Formula: see text] = 1.2 km) than were unoccupied patches ([Formula: see text] = 2.5 km). Eight of nine juvenile grouse left their natal habitat patch during autumn dispersal and net dispersal distance ([Formula: see text] = 2.3 km) was greater than that reported for grouse in areas with more contiguous habitat. Dispersing juveniles used all major forest types and 33% of relocations were in deciduous forest. Thus, deciduous forest was not an absolute dispersal barrier.

Seasonal variation in diet digestibility of pine voles

Seasonal and habitat variation in diet digestibility of pine voles (Microtus pinetorum) in four apple orchards was estimated using regression equations and the Van Soest analysis of stomach contents. The estimated percent digestible energy of diets in the four orchards varied from 57 to 72% during the year but a uniform seasonal pattern was not found among orchards. Weights of stomach contents declined markedly during winter in all four habitats.

A method of estimating diet digestibility in wild meadow voles

Regression equations for estimating diet digestibility in meadow voles (Microtus pennsylvanicus) were developed using laboratory digestion trials and chemical analyses of diets and stomach contents. These equations were used to obtain estimates of the apparent digestible dry matter (DDM) and apparent digestible energy (DE) in the diets of wild meadow voles. The estimated DDM and DE in the diets of two wild meadow vole populations varied between 62.9 and 75.2% and 62.0 and 74.2%, respectively, and were similar to those reported previously for pine voles (Microtus pinetorum).

Digestion of forage components by pine and meadow voles

A Van Soest analysis of feed and fecal samples from 24 digestion trials with pine voles (Microtus pinetorum) and 18 digestion trials with meadow voles (Microtus pennsylvanicus) was used to examine the digestive capabilities of these species and the effect of feed constituents on fiber digestion. The neutral detergent soluble fraction of feeds and forages (NDS) was the most readily available for voles. Percent neutral detergent fiber (NDF) digestibility was variable and inversely related (P = 0.0001) to the percent NDF of the diets for both pine and meadow voles. NDF digestibility was not related (P > 0.30) to the percentage of lignin in the NDF or acid detergent fiber (ADF). NDF digestion accounted for 15 and 21% of the dry matter digested by pine voles and meadow voles, respectively, on a high fiber diet (40% NDF).