Table 1.

Sampling effort and number of individual grizzly bears detected at natural bear rub sites monitored in the Northern Continental Divide Ecosystem in northwestern Montana, USA during 2004, 2009–2012.

Year	Rub sites	Sampling occasions	Cumulative rub sampling daysa	Individual grizzly bears detected
2004	4,802	4	312,882	274
2009	3,579	2	289,822	249
2010	4,608	2	344,942	334
2011	4,711	2	342,157	321
2012	4,635	2	342,972	355

The number of rub sites monitored only includes those visited ≥ 1 time after the initial visit to remove hair that could have been deposited the previous year.

^aCumulative number of days between the first visit and last collection of the year for each rub sampled per year. For example, if we surveyed 1,000 rubs 1 time after surveying them 60 days earlier, and sampled 2,000 rubs 2 times at 45-day intervals and 100 rubs 3 times at 40-day intervals, rub sampling effort for that year would be (1,000 × 60) + (2,000 × 45 × 2) + (100 × 40 × 3) = 60,000 + 180,000 + 120,000 = 360,000 rub sampling days. Sampling days began to accrue after the initial “clean-off” visit to each rub each year.