Does melanin-based plumage coloration reflect health status of free-living birds in urban environments?

Background Ecological functions and processes in urban ecosystems are governed by various human activities. City-adapted and city-exploiting animal species are expected to present certain specific behavioral and physiological traits in comparison to city-avoiders or conspecific individual frequenting less urbanized or rural environments. A trait of high importance, the plumage color polymorphism has been selected as the main study model and was correlated with different morphological and physiological parameters to highlight its importance in determining the possible health status of urban Feral Pigeons (Columba livia) in North African urban habitats.

Methods Different body morphometrics, hematological and hemoparasitic parameters were quantified on free-living Feral Pigeons in urban environments of northern Algeria. Moreover, plumage melanin-based coloration (MBC) was measured and the data collected at the individual scale was correlated with the previous parameters using linear and non-linear modeling approaches.

Results Plumage MBC scores of the sampled Feral Pigeons ranged between 0.3% and 74.8%. Among the 12 morphological traits measured, body weight, tail length and total length were deemed to be positively correlated with MBC. Darker morphs appeared to have more hemoparasites compared to lighter pigeons. Quite the same observation goes with the immunity but with non-linear trends. The number of monocytes and granulocytes increased with the increase in MBC levels in lighter morphs, while pigeons with high MBC scores exhibited negative relationships between MBC levels and the number of white blood cells.

Conclusions Despite the existence of a number of studies demonstrating phenotypic directional selection, further studies are undoubtedly necessary to understand in detail the underlying mechanisms in species life-history strategies between differently colored individuals. Findings of this correlative study open exciting perspectives revealing that MBC can be considered a good indicator of and health status and adaptation strategies to changes in urban environments.