Residential bird biodiversity and frailty deficit accumulation: a longitudinal cohort study in New York City

Urban nature is increasingly recognized as a determinant of healthy aging. However, research has largely focused on the quantity of greenness rather than biodiversity. Evidence supports an association between biodiversity and mental health, but physical aging evidence is very limited. We examined the longitudinal association between residential bird biodiversity and frailty severity using electronic health records. We conducted a retrospective cohort study of 20,388 adults aged 65 years and older receiving primary care in the Mount Sinai Health System in New York City, contributing 123,103 patient-years of follow-up (2011-2023). Residential bird biodiversity was derived from eBird citizen-science data as a modeled, bias-corrected latent Shannon diversity surface at the census-tract level yearly. Frailty severity was measured annually as the deficit count on the 31-item Veterans Affairs Frailty Index (VA-FI). We estimated associations using a negative binomial generalized additive model adjusted for age, sex, race and ethnicity, insurance, tract-level poverty, and non-Hispanic Black proportion, reporting results as the percent change in expected deficit count. We tested effect modification by age group (65-74, 75-84, over 85 years). Each interquartile range increase in residential bird Shannon diversity was associated with a 1.4% lower expected VA-FI deficit count (95% CI -2.1% to -0.8%). The association was strongest among adults aged 65-74 years (-3.0%, 95% CI -3.9% to -2.1%), attenuated among those aged 75-84 years (-0.8%, 95% CI -1.9% to 0.3%), and no longer evident among those aged 85 and older (+1.6%, 95% CI -0.0% to 3.3%). Greater residential bird biodiversity (reflecting both species richness and evenness) was associated with lower frailty severity, with the largest association in early old age. As a bioindicator of underlying environmental quality shaped by modifiable urban design, bird diversity may point to a avenue for supporting healthy aging in dense cities.