Table 1. Definitions of independent variables tested for correlation with mean daily walking distance.

Variable	Unit of Analysis	Unit	Time Scale	Description	Ref
Age	Elephant			Age of elephant (years)	[38]
Species	Elephant			African savanna or Asian	[38]
Origin	Elephant			Captive or wild born	[38]
Total Exhibit Size	Zoo	500 ft2		Total area of space available to elephants at zoo	[36]
Space Experience				The average weighted (by percent time) size of all environments in which an elephant spent time	[36]
Total	Elephant	500 ft2	Overall, Day, Night	For all environment types	[36]
Indoor	Elephant	500 ft2	Overall, Day, Night	For indoor environments only	[36]
In/Out Choice	Elephant	500 ft2	Overall, Day, Night	For environments where there is a choice of indoors or outdoors	[36]
Outdoor	Elephant	500 ft2	Overall, Day, Night	For outdoor environments only	[36]
Percent Time				Sum of monthly percent time spent in category, averaged over time period
Soft Substrate	Elephant	%	Overall, Day, Night	Time spent in environment with 100% grass, sand, or rubber substrate	[36]
Hard Substrate	Elephant	%	Overall, Day, Night	Time spent in environment with 100% concrete or stone aggregate substrate	[36]
Housed Separately	Elephant	%	Overall, Day, Night	Time spent housed in a social group of one	[36]
Juveniles (<7 years old)	Elephant	%	Overall, Day, Night	Time spent in social groups where an elephant 7 years or younger was present	[36]
Social Experience	Elephant		Overall, Day, Night	The average weighted (by percent time) size of all social groups in which an elephant spent time	[36]
Animal Contact	Elephant		Overall, Day, Night	Max number of unique elephants focal animal is in contact with	[36]
Social Group Contact	Elephant			Max number of unique social groups focal animal is part of	[36]
Recumbence	Elephant			Hours recumbent per day, averaged over all days of data collection	[29]
Herd Size	Zoo			Total number of elephants at zoo	[36]
Temperature	Zoo			Average daily temperature at zoo, averaged over all days of data collection
Enrichment Program	Zoo			Standardized factor score created using a polychoric PCA to examine the frequency of use of the different components of an enrichment program	[37]
Enrichment Diversity	Zoo			Shannon diversity index score of enrichment activities types and frequencies conducted at zoo	[37]
Exercise Diversity	Zoo			Shannon diversity index score of exercise types and frequencies conducted at zoo	[37]
Feeding Diversity	Zoo			Shannon diversity index score of feeding types and frequencies conducted at zoo	[37]
Feeding Predictability	Zoo			The predictability of feeding times; categorical where 1 is predictable, 2 is semi-predictable, and 3 is unpredictable	[37]
Feed Total	Zoo			Sum of the number of feedings during the day and number of feedings during the night	[37]
Alternate Feeding Types	Zoo			The proportion of all feedings where food was presented in a foraging device, hidden, or hung above the exhibit	[37]
Spread	Zoo			The proportion of all feedings where food was spread through the exhibit	[37]