Long-term radiotelemetry was used to study patterns of den use and winter movement in porcupines (Erethizon dorsatum) in New York. Six of eight animals used dens regularly; the rest spent most of their winters in the shelter of hemlock stands (Tsuga canadensis). Animals entered dens in October–November after minimum daily temperatures had fallen below 0 °C for 6.8 days. Before this period, animals used temporary dens in response to rain or cold weather. Dens were abandoned in April when minimum daily temperatures rose above 0 °C and snow cover melted. Animals that left dens early typically sought the shelter of hemlock stands. Animals changed dens, on average, every 23 days. A single den-using adult male changed dens every 9.3 days. Den change was stimulated by disturbance. Animals showed strong year to year den fidelity. Animals shared dens 12% of the time. In all cases where sharing animals could be identified, they constituted a male–female pair that had previously shared a summer territory. Animals denned only in ready-made cavities such as rock outcrops, live hollow trees, outbuildings, and hollow logs. Heat-conserving features of such dens and of hemlock shelters are discussed. For three of four winters of the study, winter range averaged 7.4 ha, 11.4% of the nonwinter range. During the fourth winter, when snowfall was only 40% of normal, winter range did not differ significantly from nonwinter range.
Porcupine quills possess antibiotic properties. The antibiotic activity is associated with free fatty acids (but not neutral lipids) coating the quills. Extracts of quill fatty acids strongly inhibited the growth of six grampositive bacterial strains. No growth inhibition was observed against four gram-negative strains. Free fatty acids made up 18.6% of total quill lipids in samples collected in the summer, and 5.5% of total lipid in samples collected in the winter. The fatty acids were separated and identified (as the methyl esters) by gas-liquid chromatography and mass spectroscopy. Major components of a complex mixture included 14-methylpentadecanoic, 9-hexadecenoic, hexadecanoic, and 9-octadecenoic acids. It is suggested that porcupines benefit from the quill fatty acids: evidence from healed fractures of major skeletal components (35.1% incidence in 37 skeletons examined) suggests that porcupines fall relatively frequently from trees. Quill antibiotics may limit self-injury suffered in such falls.
The histology of the porcupine's skin and subcutis is described. The functional relationships of the thoracic skin during elevation of the quills involve a smooth arrector muscle attached to quill sets, one set behind the other, with the muscle at a slant usually from a single root tip of one set to the distal part of the follicles in the caudal set. Stretched elastin returns the quills to their resting position. There is a low-resistance pathway for the tilting quill roots through loose connective tissue and fat until a collagenous strand attached to the quill set stops further tilt. The lumbosacral region (rosette) has a two-layered arrector, but it attaches to only its own quill set and inserts into the dermis. Both regions have a varied and complicated system of transverse and oblique muscles associated with the roots in a set. (The occurrence of obliques is variable in the thoracic region.) A hypothesis is presented concerning the mechanism of quill detachment from the porcupine after the quill is rammed into a predator. This involves the shearing of the conical root tip along its adherent follicular cells and a stopping device (spool) to prevent the root from self-stabbing.
Winter feeding of individual porcupines (Erethizon dorsatum L.) was studied in the northern Catskill Mountains of New York by following individual feeding trails in the snow. The study population as a whole fed primarily on beech (Fagus grandifolia) and sugar maple (Acer saccharum) and less frequently on eight other tree species. Individual porcupines limited their feeding to one or two species. An individual's primary food choice corresponded to the numerically most abundant tree species in its foraging area; its secondary food choice could not be related to relative density nor to relative basal area.
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