Investigating the Impact of Acoustic Environment and Human Presence on Okapi Faecal Glucocorticoid Metabolites

The influence of visitor behaviour and sound pressure levels on zoo animals remains unclear.

This study examined associations between sound pressure levels, visitor numbers and faecal glucocorticoid metabolites (FGCMs) in a male okapi (Okapia johnstoni) at a UK zoo.

Data were collected across two 5-day periods representing high- and low-visitor seasons, yielding 10 days of acoustic recordings and matching FGCM samples. Acoustic metrics were calculated for the open and closed periods of the zoo (LeqZ, L10Z and L90Z). Statistical analyses included the Wilcoxon and Welch t-tests, as well as Pearson correlations and multiple linear regression models.

LeqZ and L10Z did not differ between seasons, whereas background noise (L90Z) was higher in the low season (t = -4.42, P = 0.005). Sound levels were generally higher during open hours in both seasons. Correlations between visitor numbers and acoustic metrics were weak and non-significant (high season LeqZ × visitors: r = 0.005, P = 0.994; low season: r = -0.347, P = 0.567). FGCM concentrations did not differ between seasons (72a: P = 1.00; 72T: P = 0.37). Regression analyses showed that LeqZOpen positively predicted 72T FGCMs (β = 5.30 ± 1.85, P = 0.02), while visitor numbers negatively predicted 72T (β = -0.04 ± 0.02, P = 0.04). Visitor numbers did not differ between seasons.

Okapi adrenocortical activity appears more responsive to acoustic conditions than to visitor numbers, suggesting noise as the primary stressor. Reducing noise through enrichment or vegetation may improve okapi welfare.