Ecological Archives A025-094-A2

John W. Pokallus and Jonathan N. Pauli. 2015. Population dynamics of a northern-adapted mammal: disentangling the influence of predation and climate change. Ecological Applications 25:15461556.

Appendix B. Additional data collection methods and results of preliminary analyses for estimating juvenile porcupine survivorship rates at Sandhill Wildlife Area.

Porcupines fitted with radio collars were immobilized using oxygen-carried isoflurane and, in addition to the handling procedures described above, had their quills clipped down to the skin with an electric trimmer where the collar would be placed to reduce abrasion and irritation.

We were unable to incorporate two of the 26 radio-collared porcupines due to one instance of collar failure and one mortality prior to parturition. Each porcupine was relocated once every three days. Upon locating the adult female, we searched in a circular pattern with an approximate 30-meter radius of the individuals’ location to identify potential offspring.

Because young may have been present but were undetected during searches we determined pregnancy and lactation status of the adult females for which we had not detected a juvenile. In mid-May we captured all radio-collared females that had not been located with a juvenile and palpated to determine pregnancy status, and, if not pregnant, administered a single, 1 mL intramuscular injection of oxytocin to induce lactation to identify whether they were actively nursing (Hale and Fuller 1996). If the female porcupine produced milk, it was included as reproductively active in our fecundity estimates irrespective of whether a juvenile was located (n = 3).

Once juveniles were located in the field, they were transported indoors where they were weighed, sexed, PIT-tagged, and surgically implanted with an intraperitoneal VHF transmitter (model IMP-130; Telonics, Mesa, AZ, USA). All surgeries were performed under aseptic conditions. Juvenile porcupines were anesthetized with oxygen-carried isoflurane. Once induced, we administered Excede (ceftiofur crystalline free acid) at a single dosage of 5.0 mg ceftiofur equivalents (CE)/kg body weight and Baytril at 10.0 mg/kg body weight prior to surgery. A 4 cm incision was made along the linea alba and the sterile transmitter was inserted into the peritoneal cavity and allowed to float freely. We closed the incisions in the muscle and skin tissue layers with absorbable braided sutures (Vicryl, 3-0). Following surgery, juveniles were monitored until they were ambulatory and immediately released at the site of capture. Upon release, juvenile radio signals were monitored for mortality signals daily until 14 July, at which point they were monitored twice weekly through December.

Upon detection of a juvenile mortality signal, we located the mortality site, recorded a description of the site and the remaining carcass to categorize the cause of mortality as fisher depredation, unidentified depredation, or non-depredation. Fisher depredation events were identified by the fishers’ unique method of killing a porcupine, characterized by the absence of all bones, entrails, and muscle and fat tissue, the only remains consisting of a mostly-intact hide and tail as a result of quill avoidance (Roze 2009). Unidentified depredations were categorized as predatory events with characteristics other than those described for fisher, including the presence of tissue and bone, the absence of the carcass entirely, and transmitter signal loss. Two unidentified events were recorded as a result of transmitter signal loss. In each instance of signal loss, the maternal porcupine was located and the area around its location thoroughly searched for signs of a juvenile or depredation event as well as sign of predator activity in the area. The presence of predator sign near the most recent location of the two lost-signal individuals indicate that a predatory event was likely, both mortalities were consequently included in the unidentified predation category. Non-predatory events where determined by an intact carcass devoid of bite marks.

Table B1. Cox Proportional Hazard analysis for juvenile porcupines (Erethizon dorsatum) at Sandhill Wildlife Area from 23 April to 15 October 2012. A priori model structures are arranged by the parameters of interest with the following notation: Mass = weight of juvenile at time of first location, CC = % canopy cover at first location, CT = categorical variable of cover type (deciduous forest, woody wetlands, shrub/scrub, emergent herbaceous wetlands), SA = age of forest stand at first location, Date = date of first location. The top listed model, “Mass” was the only model to be significant (p = 0.02), suggesting that increased juvenile mass reduced the hazard of mortality among juvenile porcupines.



Exp(β)  (95% CI)


Logrank p



0.96  (0.93 - 0.99)





1.01  (0.98 - 1.04)



Maternal condition


0.73  (0.40 - 1.34)





1.00  (0.97 - 1.02)





1.55  (0.85 - 2.82)





1.01  (0.98 - 1.05)




Literature Cited

Hale, M. B., and T. K. Fuller. 1996. Porcupine (Erethizon dorsatum) demography in central Massachusetts. Canadian Journal of Zoology 74:480–484.

Roze, U. 2009. The North American porcupine. Second edition. Cornell University Press, Ithaca, New York, USA.

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