Foxes are strongly dependent on dens for parturition and rearing of cubs. Due to the shallow permafrost-free layer in most of the arctic fox’s range, new dens are rarely dug and existing ones are often used repeatedly year after year. An effective way to monitor both arctic and red fox populations is to take advantage of their use of den sites for reproduction.
Starting in 1993, known den sites in the south plain of Bylot Island were opportunistically visited to assess the presence of cubs. Starting from 2003, the monitoring became systematic. An extensive search of dens was conducted and covered an area of ca. 600 km2 going from the Qarlikturvik valley to Pointe Dufour. Since then, dens are visited twice during summer, once in mid-May and once at the end of June. All visits are made within a week to avoid counting the same litter twice due to relocation of cubs during the rearing period. Only dens where cubs are seen or heard are categorized as breeding dens (natal or rearing den). Since 2007, camera traps are installed on some dens to complement field observations.
