2. Materials and Methods
2.1. Subjects and Setting
Two captive-born grizzly bears were the subjects of the study: Keema, and Denali, ~395 kg male bear and ~405 kg male bear, respectively. Both bears were 15-years-old at the study’s onset and were reproductively intact. They were a brother pair that came from Washington State University’s Bear Center in Pullman, Washington, and resided at the Woodland Park Zoo (Seattle, WA, USA) since November of 1994.
The bears resided in an exhibit in the Northern Trail zone of the zoo, and that contained three areas: An on-view outdoor area, ~1120 m2
, an off-view outdoor exercise yard, ~410 m2
, and a indoor space, ~250 m2
. Both outdoor areas consisted of natural trees, deadfall, grass, and rocks. The on-view area also contained an artificial river that led to a viewing window pool that held ~95 kL of water (see Figure 1
and Figure 2
Feeding enrichment was routinely provided in the form of scatter feeds and through devices, such as boomer balls in both outdoor areas. The indoor space consisted of individual dens for each of the bears. The indoor dens provided the bears with the opportunity to hibernate in the winter, although their regular feeding schedule made this unnecessary (see below). The bears were typically moved from the off-view area to the on-view area by 09:00 h, and then limited to the on-view area of the exhibit between 09:00 and 16:00 h (Fall/Winter; October–March) or 09:00 and 18:00 h (Spring/Summer; April–September), with some variability depending on weather conditions.
Diets for the bears varied based both on the individual and time of year, with 4.5–7 kg consumed per bear per day. The bear diet consisted of Mazuri® omnivore diet, whole chickens, trout, rabbits, yams, carrots, apples, honeydew melon, papaya, pears, cantaloupe, blueberries, romaine lettuce, celery, kale, and grass hay. Salmon, ground turkey, oranges, and alfalfa were also occasionally added to their diet, depending on availability. Treat items used for enrichment and/or training sessions included MarionTM leaf eater biscuits, Purina Omolene®, IamsTM dog food, and peanut butter. Diets were provided to the bears either twice a day (07:30 and 15:00 h) or three times a day (07:30, 11:00, and 15:00 h), dependent on their seasonal activity. The majority of their diet (at least half their daily diet) was provided at the 15:00 h feeding.
Materials included Palm® handhelds used to record behavioral data and an Event-PC program that was run on the Palm® handhelds and designed specifically for this experiment by James C. Ha at the University of Washington. Other materials included a notebook used to record potential errors and additional observations/field notes that occurred during a session.
2.3. Data Collection and Procedure
Prior to its implementation, the study was approved through Woodland Park Zoo’s Research Committee, as well as the University of Washington’s Institutional Animal Care and Use Committee (IACUC #2858-06). An ethogram modified from a prior zoo bear study [37
] and consisting of 17 behaviors split into seven classes of behaviors was also developed prior to the implementation of the study (see Table 1
The behaviors observed were mutually exclusive, and the inclusion of the “Other” observation category made the ethogram exhaustive. A modified scan sampling procedure [53
] was used to record behaviors for both bears during all observation sessions. The number of bears on exhibit was recorded for behavior every 30 s for 30 min of observation for each session. These observations were then averaged for each session based on the total number of bears engaging in each behavior, and by a class of behavior. All observations were conducted in the on-view outdoor portion of the exhibit between 09:30–18:00 h, seven days a week, between 12th January 2010 and 26th January 2011 (902 total observations (1–8 observations per day) for 451 total hours of observations). Observers were typically registered for independent research credit through the Psychology Department at the University of Washington (PSY 499) and received observation training by live training sessions at the beginning of each semester and weekly lab meetings throughout the study. Observations were examined weekly by the first author for consistency across all observers, and drift was accounted for during these weekly checks, as well as through weekly lab meetings. All observations were scheduled on a semester basis, with observers filling times available during the week to account for as many observational times as possible. A total of 38 observers collected behavioral data for the entire study.
2.4. Statistical Analyses
SigmaStat, version 11.0 (Systat Software Inc., San Jose, CA, USA) was used to run all the statistical analyses. Only the classes of behavior that occurred more than 5% (Active, Forage, Inactive, and Stereotypy) were examined for month-to-month, seasonal, and hour-to-hour activity, as well as statistically analyzed. Because Shapiro-Wilk tests for normality failed, the differences for the four classes of behavior were tested for seasonal differences (Winter: December–February, n = 232 sessions; Spring: March–May, n = 325; Summer: June–August, n = 136; Fall: September–November, n = 209) using Kruskal–Wallis analysis of variance (ANOVA) on ranks tests. When significant differences (p < 0.05) for the ANOVAs were found, post-hoc pairwise comparisons (using Dunn’s Method) were implemented. Differences between the two combined January months (2010 (n = 38 sessions) and 2011 (n = 47 sessions); n = 85 total January sessions) and July (2010; n = 55 sessions) were tested using Mann-Whitney U tests. The two January months were combined after finding no significant differences between each class of behaviors (also Mann-Whitney U tests). January and July were directly compared because they were representative months for further examinations of the seasonal differences between the traditional winter (January) hibernation and summer (July) activity periods.
Overall, Inactive was the most frequently occurring class of behavior (M
= 57.8%, SE
= 1.2%), followed by Active (M
= 22.9%, SE
= 0.8%), Forage (M
= 7.8%, SE
= 0.5%), Stereotypy (M
= 5.9%, SE
= 0.4%), Other (M
= 4.1%, SE
= 0.4%), Social (M
= 1.2%, SE
= 0.2%), and Groom (M
= 0.4%, SE
= 0.1%). Figure 3
shows the month-to-month activity for the 13 months of observation.
During January through March, Inactivity was the most frequent class of behavior, occurring on average above 75% of all behaviors recorded. All other classes of behaviors during these months occurred ~10% or less. Starting in April, Active rose to 18% (SE = 1.5) of all behaviors recorded, until Active peaked in August at almost half of all behaviors observed (M = 46%, SE = 5.1). The Stereotypy class of behaviors occurred ~3% or less of behaviors recorded during all observations, except for May through July: 19.9% (May; SE = 1.8), 18.4% (June; SE = 2.7), and 17% (July; SE = 2.6). The Forage class of behaviors remained relatively stable, ranging from 5–10% of all behaviors recorded.
shows the comparison between the four seasons:
All four classes of behaviors tested for differences across the four seasons showed a statistically significant effect: Active (x23 = 123.230, p < 0.001), Forage (x23 = 14.949, p = 0.002), Inactive (x23 = 115.395, p < 0.001), and Stereotypy (x23 = 133.534, p < 0.001). For Active, post-hoc tests showed a significant difference when comparing the winter to all other seasons and also the spring to both the summer and fall (p < 0.05 for all). Active increased from 11.2% (SE = 0.9) in the winter to 19.5% (SE = 1.1) in the spring, increased to 32.5% (SE = 2.3) in the summer, and increased to 35.2% (SE = 1.8) in the spring. For Forage, post-hoc tests showed a significant difference when comparing the spring to both the winter and fall (p < 0.05 for both). Forage increased from 6.5% (SE = 0.9) in the winter to 9.0% (SE = 0.9) in the spring, decreased to 7.6% (SE = 1.3) in the summer, and decreased to 7.3% (SE = 1.0) in the spring. For Inactive, post-hoc tests showed a significant difference when comparing the winter to all other seasons and the spring to the summer (p < 0.05 for all). Inactive decreased from 77.4% (SE = 1.7) in the winter to 56.8% (SE = 1.9) in the spring, decreased to 41.2% (SE = 3.1) in the summer, and increased to 48.2% (SE = 2.3) in the spring. For Stereotypy, post-hoc tests showed a significant difference when comparing the winter to all other seasons and also the summer to both the spring and fall (p < 0.05 for all). Stereotypy increased from 0.3% (SE = 0.1) in the winter to 9.0% (SE = 0.9) in the spring, increased to 13.8% (SE = 1.5) in the summer, and decreased to 2.0% (SE = 0.3) in the spring.
To further examine the behavioral differences that occurred seasonally, we compared two months (January and July), which in the wild would be representative of winter hibernation and summer activity periods, respectively. Figure 5
shows the comparison between the two combined January months and July:
Three of the four classes of behaviors tested for differences between January and July showed a statistically significant effect: Active (U138 = 1265, p < 0.001), Inactive (U138 = 1145, p < 0.001), and Stereotypy (U138 = 783.5, p < 0.001). Between January and July, Active increased from 9.9% (SE = 1.5) to 29.5% (SE = 3.4), Inactive decreased from 77.2% (SE = 3.1) to 41.5% (SE = 5.0), and Stereotypy increased from 0.2% (SE = 0.2) to 17% (SE = 2.6).
shows the hour-to-hour activity for the two combined January months and July.
In the January months (both 2010 and 2011), when the bears were observed in the on-view area of the exhibit from 09:00–16:00 h, Inactive occurred from the morning until 13:00 for > 90% of all observations. As Inactive decreased to ~30% by the 15:00–16:00 h period of observation, both Active and Forage increased from 11.6% (Active) and 5.4% (Forage) to 22.3% and 22.4%, respectively. During July, Inactive remained below 20% except for during the 10:00–11:00 h (35.3%) and 11:00–12:00 h (28.3%) periods, and then later increased, beginning at 15:00–16:00 h from 49.5% to 91.1% and 100% during the 16:00–17:00 and 17:00–18:00 h periods, respectively. Active, Forage, and Stereotypy showed two peaks in activity, with Active beginning high (39.2%) from 09:00–10:00 h, decreasing, and then peaking to their highest occurrence from 14:00–15:00 h at 67.5%. Forage occurred in its highest frequency during the 11:00–12:00 h (22.3%) and the 15:00–16:00 h periods (9.8%). Stereotypy occurred in highest frequency from 10:00–11:00 h (48.4%), decreased, and then peaked again to 28.6% during the 13:00–14:00 h period of observation.