The Apparent Urban Advance in Juvenile Vulpes vulpes Observations Diminishes after Accounting for Switzerland's Elevational Structure

Daniel Fadrique-Barbero 

Urbanization can alter wildlife life cycles, but comparisons between more and less urbanized environments may be confounded by other environmental gradients. This study analyzed 4295 human-reported observations of \textit{Vulpes vulpes} from 496 generalized \(5 \times 5\ \mathrm{km}\) cells across Switzerland between 2018 and 2024 to estimate when the probability that a spring record contained juveniles increased. Without environmental adjustment, the most built-up cells reached a 30\,\% probability threshold approximately 4.7 days earlier than the least built-up cells (95\,\% confidence interval: 0.2--8.4 days earlier). Temperature had little influence on this contrast. However, the most built-up cells were also located at considerably lower elevations, and joint adjustment for temperature and elevation reduced the contrast to 0.7 days in the opposite direction (95\,\% confidence interval: \(-3.8\) to \(+7.7\) days). Analyses using an alternative elevation measure, different probability thresholds, comparable elevation ranges, and a conservative treatment of potential duplicate records produced consistent results. These data therefore provide insufficient evidence for an independent urban advance and instead show how the elevational structure of Switzerland can generate an apparent timing contrast. The result describes the observable timing of records containing juveniles, not the dates of birth or den emergence.