Recordings of heart rate (HR) and levels of activity were obtained from March 10, 2009 to September 1, 2014 (2002 days) in an adult female American black bear (#2213; the “Spider Lake bear”). This time period included parturition and the rearing of 3 litters of cubs (born in January of 2009, 2011, and 2013). Cubs remained with their mother through one winter and the following spring, at which time the yearlings separated and she again mated; thus, she was solitary only during the summers and autumns of 2010, 2012, and 2014. Figure 1 plots the daytime HR, nighttime HR, and daily amount of activity for each of the 6 years; Fig. 2 displays the same dataset as weekly averages overlaid for the 6 years to demonstrate the remarkable consistency in patterns and levels of HR and activity. Table 1 summarizes a number of parameters relating to HR, behaviors, and variations in weather. Table 2 provides the monthly summaries for daytime HR, nighttime HR, and daily activity for the entire time period, noting years with cubs and yearlings.

Figure 1: Average daytime and nighttime HR and total daily activity in each of six years for an adult female black bear in northern Minnesota. Peak daily values are shown each year. Cubs were born in January of 2009, 2011, and 2013 and remained with the mother for 17 months. Asterisks denote den visits by the research team: the heart rate was elevated due to the effects of the anesthetic agent which eliminates autonomic tone and the respiratory sinus arrhythmia. Full size image

Figure 2: Weekly averages for daytime HR, nighttime HR, and total daily activity for a female black bear, demonstrating year to year consistency. The bear had year-old cubs (yearlings) in the spring of alternate years, and was solitary in summer and autumn of these years. Increasing HR and activity occurred throughout the spring, but was delayed in 2014 following a colder winter. (The period of January-March in 2014 was colder than the same period in all other periods; p < 0.0004 for all comparisons). Full size image

Table 1 Tabulation of physiological and behavioral parameters and weather recorded during six years in the life of female black bear #2213 in northern Minnesota. Full size table

Table 2 Tabulation of physiological and behavioral parameters recorded during six years in the life of female black bear #2213 in northern Minnesota. Full size table

Over the 6 consecutive years, HR steadily increased over roughly a 12 week period each spring from hibernation levels (20–25 beats/minute (bpm)) to summer active levels (July daytime HR averaged 95 bpm and nighttime HR averaged 78 bpm). Maximum average daytime HR ranged from 104–125 bpm and maximum average nighttime HR ranged from 113–149. Daily activity was as low as 0 minutes/day during hibernation, averaging <12 minutes/day, with maximum daily activity ranging from 900–1116 minutes (15.0–18.6 hours) per day. Total annual activity was remarkably consistent, ranging from 105,508–112,895 minutes of movement/year (1,758–1,882 hours/year; averaging 13.5 hours/day in July).

Emergence from hibernation and departure from the den site, as evidenced by consistent activity and sustained HRs of greater than 40 bpm, occurred from 25-Apr to 04-May in 5 of the years. This occurred later in 2014 (17-May) presumably due to the colder weather that year (colder than all other periods of Jan-Mar; p < 0.0004 for all comparisons of daily averages; 2014 Jan-Mar mean = −14.2 C, min = −30 C, max = 4.4 C). Presumed denning in the fall, as evidenced by sustained HRs of less than 40 bpm, occurred during 23-Sep to 23-Oct. Each year, the bear switched from primarily diurnal activities to primarily nocturnal: this switch occurred between 22-Jul and 24-Aug, and was on nearly the same day in 4 of 6 years (13-Aug, 13-Aug, 16-Aug, and 18-Aug; Table 1).

We identified dates of parturition in 2011 and 2013 (04-Jan and 11-Jan, respectively). (See Supplementary Video V1.) Parturition was marked by increased HR during the second week of January (daytime average HRs = 32.5 v. 16.6 bpm in alternate years, p = 0.015; average nighttime HRs = 32.4 v. 16.1 bpm in alternate years, p = 0.008). Other statistically significant differences included higher average daytime HRs during March with newborn cubs than with yearlings (33.7 v. 21.3 bpm, p = 0.045), higher average daytime HRs in June when solitary (77.4 v. 70.8 bpm, p = 0.010), and more active in July when solitary (856 v. 768 minutes/day, p = 0.019), but more active in September with cubs (602 v. 349 minutes/day, p = 0.014).

Extreme respiratory sinus arrhythmias were elicited during winter months, with HRs as low as 10 bpm, sinus pauses of up to 14.4 seconds, and respiratory rates as low as 1.5 breaths/min (Fig. 3). By contrast, during summer active periods, HRs as high as 231 bpm were recorded (Fig. 4). During our visits to the bear’s denning sites while she was hibernating, the devices recorded transient spikes in HRs (Fig. 1) likely due to both the effects of the anesthetic agents and the presence of our research team (pre-anesthesia). The HR increases associated with a typical visit is shown in Fig. 5, with rates returning to those of undisturbed hibernation within 6–8 hours.

Figure 3: Respiratory sinus arrhythmia and long sinus pause recorded from female black bear #2213. An electrocardiogram (ECG) is shown for 18-Dec-2009 at 12:21. A 14.4 second pause occurred following acceleration in heart rate with inspiration. Full size image

Figure 4: An electrocardiogram from female black bear #2213 on 07-Sep-2011 recording a ventricular tachycardia with an average heart rate of 227 beats/minute and a maximum heart rate of 231 beats/minute. This episode occurred during the legal hunting season in 2011, but whether it was related to a human interaction is unknown. The interval between consecutive heart beats is shown at the bottom of the strip recording (260 milliseconds = 231 bpm). Tachycardia detection occurred when 16 consecutive heart beats exceed the programmed detection setting of 176 bpm, at which time the device stored the associated ECG in memory. Full size image

Figure 5: Heart rate recordings of a female black bear in northern Minnesota during a visit to her den by the research team. A two month interval of daily average daytime and nighttime HR is plotted, with a 12 hour window inset (07-Mar-2014) showing the average HR every two minutes (plot starts at the time of the team’s departure at 11:30 AM). The HR returned to pre-visit levels typical of winter hibernation within approximately 6–8 hours. Full size image

Device monitoring ended when this bear was legally shot and killed by a hunter in September, 2014. Her HR before sunrise averaged 60 bpm, then increased to about 120 bpm for an hour; her final HR averaged 188 bpm (Fig. 6).