Lemmings drive tundra vertebrate food webs, yet ethical and logistical constraints still limit spatially explicit monitoring. We introduce and evaluate a low-cost “pee-card” method that indexes collared lemming (Dicrostonyx groenlandicus) abundance from urine marks, and compare it with snap-traps and incidental observations. Across four transects (20 stations each) over three summers (2019, 2023, 2025) at Alert, Nunavut, we deployed 240 pee-cards per year (3 per station; 720 total) and then placed snap-traps at the same micro-sites. Each method was run for three consecutive 24-h periods. Pee-card detections were positively associated with snap-trap captures, with models including year and transect explaining additional variation. Using traps as the reference, pee-cards showed high sensitivity (93%), moderate specificity (52%), and balanced accuracy of 72%, with very few false negatives. Patterns held with and without fresh lemming signs of activity. Accumulation curves indicated that pee-cards saturated by the second 24-h period and, after three periods, identified presence at more than twice as many stations as traps. Pee-cards may provide a scalable, non-invasive index of collared lemming presence and abundance, potentially enabling efficient, ethical monitoring at broad spatial scales.

We conducted a multi-year field experiment at Canadian Forces Station Alert, Nunavut (82°30′N, 62°20′W) to develop and validate a non-lethal “pee-card” method for indexing collared lemming activity and to benchmark it against snap trap captures. In each of three summers (2019, 2023, 2025), we established four 285-m transects (A–D) with 20 permanent stations at 15-m intervals (240 stations per year). At every station, three temporary micro-sites were selected within 4 m of the stake (newly chosen each year). Pee-cards (3 × 8 cm corrugated polypropylene) were left for three consecutive 24-h periods, and checked each morning; observers recorded urine marks ≥1 mm and whether the card was at a burrow and/or near fresh sign. Immediately afterward, each micro-site received a Museum Special snap trap (≈14 × 7 cm), baited with peanut butter and operated for three consecutive 24-h checks. Across years this design yielded 720 pee-cards and the same number of subsequent trap placements. All work followed approved animal-care and territorial permits.