Behavioral Plasticity Under Urban Stress

Abstract

Urban environments impose chronic stressors -- noise pollution, light at night, human presence, food subsidy, and altered predation regimes -- that differ fundamentally from rural environments and select for behavioural plasticity enabling flexible adjustment of activity patterns, foraging behaviour, boldness, and acoustic communication. This study quantified behavioural plasticity in 12 vertebrate species (8 bird species: European blackbird Turdus merula, common starling Sturnus vulgaris, house sparrow Passer domesticus, great tit Parus major, feral pigeon Columba livia, peregrine falcon Falco peregrinus, carrion crow Corvus corone, and barn swallow Hirundo rustica; 4 mammal species: urban fox Vulpes vulpes, badger Meles meles, hedgehog Erinaceus europaeus, and house mouse Mus musculus) across 42 paired urban-rural sites in Madrid, Stockholm, and Vienna (2020-2024). Using GPS tracking (284 GPS-collared individuals), acoustic recording (2,840 song recordings for birds), cortisol measurement from faecal samples (n = 2,840), and standardised novel object test and open-field test, urban populations showed: 3.84-fold higher nocturnal activity relative to rural conspecifics (driven by artificial light at night; r = +0.84 with ALAN intensity), significantly earlier dawn singing in urban birds (-24.4 +/- 6.4 minutes relative to rural; p < 0.001), significantly higher song frequency in urban environments (+842 +/- 184 Hz; p < 0.001; consistent with noise masking avoidance), 2.84-fold higher boldness scores in novel object tests, and higher baseline faecal glucocorticoid concentrations (fGCM; +38.4 +/- 8.4%; p < 0.001). A Behavioural Plasticity Index (BPI) integrating activity, acoustic, and stress response components explained 74.4% of the variance in urban vs. rural classification. Species with higher BPI showed significantly higher urban abundance relative to rural (r = +0.74, p < 0.001), confirming that behavioural plasticity is the primary predictor of urban colonisation success.