Monitoring compliance with environmental laws is essential to overcoming possible implementation shortfalls jeopardizing their effectiveness. Besides improving our ecological understanding of wildlife, remote tracking technologies also allow us to take advantage of such ecological knowledge to use wildlife as sentinels of compliance with law.

We illustrate this sentinel potential of wildlife using GPS-tracking of large scavengers with complementary functional traits (i.e., 21 griffon vultures and 13 wolves) to assess compliance with EU sanitary regulations allowing livestock carcass disposal in the field. Wildlife sentinels allowed the systematic evaluation of 489 livestock carcasses left in the field, which revealed an important mismatch between on-paper and in-reality implementation of these regulations. While <45 % of the carcasses were placed in authorized areas, compliance with all the criteria required by the regulations on livestock carcass disposal (e.g., from carcass characteristics such as species, age, or production system to its location far away from water, buildings, or roads) ranged from 0 to 4.2%, with no major differences between regions with uneven implementation. Major gaps in compliance pointed towards insufficient and over-bureaucratized designation of Scavenger Feeding Zones (SFZs), where livestock carcass disposal is authorized. The indiscriminate nature of distance criteria from carcasses to watercourses, buildings, and infrastructure further affected compliance.

Synthesis and applications: GPS-tagged scavengers allow the on-ground monitoring of carcasses, the addressing of potential risks for wildlife, livestock, and human health, the quantitative assessment of compliance with the law and would improve estimates of carcass availability, substantially contributing to more effective legislation enforcement. Our results show the huge potential of GPS-tagged wildlife as sentinels for monitoring compliance to enhance the environmental rule of law.