Pee-cards: A new, inexpensive and humane technique to index collared lemming abundance

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. 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 provide a scalable, non-invasive index of collared lemming abundance, enabling efficient and ethical monitoring at broad spatial scales. The method may also be suited to other simple small-mammal systems in which a single species reliably deposits urine on cards.