Plumage Polymorphism Varies Along Climatic and Urban Gradients Across Global Cities
Jaeseung Kim, Duri Bae, Changku KangABSTRACT
Aim
How phenotypic variation relates to both climatic gradients and urbanisation across spatial scales remains unclear at global scales. Although animal colouration has long been linked to climate through ecogeographical rules, and urbanisation has increasingly been associated with phenotypic change, these processes have rarely been evaluated together across broad spatial extents within a single analytical framework. Here, we tested whether worldwide variation in plumage polymorphism is associated with climatic gradients consistent with ecogeographical rules, and whether urbanisation is associated with shifts in melanisation and morph composition consistent with colour homogenisation or divergence.
Location
Global cities.
Time Period
2015–2025.
Major Taxa Studied
Feral pigeon (
Methods
Using deep‐learning image analysis, we identified pigeons in citizen‐science images and classified 240,098 detections into seven plumage morphs. We then modelled spatial variation in plumage morph composition using Bayesian hierarchical models that partitioned variation into differences among cities and local variation within cities. We quantified climatic and urbanisation associations using posterior‐derived measures of melanisation, morph diversity and morph composition, and assessed regional heterogeneity across six continental‐scale geographic regions.
Results
Climate and urbanisation showed contrasting associations with plumage polymorphism across spatial scales: climatic variation was more strongly associated with morph composition among cities, whereas urbanisation showed clearer associations within cities. Among cities, melanisation increased toward colder environments, a pattern broadly consistent with Bogert's rule, although it was driven primarily by shifts between the two most common morphs and varied across regions. Within cities, urbanisation was positively associated with melanisation and morph diversity. Evidence for a general association between humidity and melanisation was weak and sensitive to how climatic variation was represented.
Main Conclusions
Our work reveals distinct scale‐dependent climatic and urban signatures in phenotypic variation, while highlighting that broad ecogeographical patterns may be regionally contingent rather than universally expressed.