Preprint · Jul 18, 2026
Biological age varies across the breeding distribution of a migratory warbler
By Sutton M, Rodriguez M, Kim H et al.
Biological senescence reflects the cumulative physiological accumulation of environmental and intrinsic stressors. Senescence can influence demographic rates such as survival, reproduction, and population dynamics. Although environmental conditions are expected to shape biological aging, little is known about how biological age varies across wild populations. We quantified telomere length in 122 male hermit warblers (Setophaga occidentalis) sampled across six sites spanning the breeding range in the Pacific Northwest. We evaluated whether telomere length was associated with environmental, geographic, social, and individual factors, including vegetation structure, climate, elevation, conspecific density, age, and body size. Mixed-effects models suggest that birds occupying high-elevation territories had significantly longer telomeres relative to the population, indicating lower biological age. Vegetation structure, climate, age, and body size showed little association with telomere length. We found weak evidence of a negative relationship between conspecific density and telomere length, suggesting that competition may contribute to biological aging, although this effect was less supported. Because telomeres integrate cumulative oxidative stress across a lifetime, our results indicate that environmental context is associated with biological age. These findings provide a physiological perspective on how environmental gradients may influence individual condition in wild populations.