Breeding ecology of the common myna (Acridotheres tristis): rural nestlings exhibit enhanced growth compared to urban conspecifics

This study was conducted in urban and rural areas of the Mardan District, Khyber Pakhtunkhwa, Pakistan. The urban site was situated in the built-up area of Mardan City (34°11′ N, 72°02′ E) with paved surfaces, traffic, and permanent night lights. The rural region included low-density agrarian villages surrounded by a variety of agricultural fields, riparian vegetation, and a few artificial lights. The rural location of the study site was approximately 30 km from the city center in the cultivated peripheries of Mardan. Mardan has a hot, semi-arid climate, with a mean annual temperature of 22.2 °C and a mean annual rainfall of 559 mm (Sadam et al. 2021). During the breeding season (March–August), mean monthly air temperatures in Mardan range from 22 °C in March to 34 °C in June, with maxima often exceeding 40 °C in June–July. The mean monthly precipitation is low (Using nestboxes, we compared the breeding ecology and nestling growth of the common myna (Acridotheres tristis) in urban and rural environments of Mardan, Pakistan. Nestbox occupancies were higher in rural areas, but both rural and urban nestboxes were rarely and unsuccessfully reused for the second breeding. Fledging success was closely related to box orientation, and east-facing boxes had the greatest number of fledglings in both habitats. Nest architecture within the boxes differed considerably, with nest construction taking longer at urban sites than at rural sites. Urban nests were heavier, with smaller outer diameters but slightly larger inner diameters, whereas nest depth did not differ between habitats. Urban nests contained anthropogenic materials (plastic) and feathers, whereas rural nests primarily contained natural plant materials. Urban pairs began breeding earlier than their rural counterparts; however, rural nests had longer incubation and nestling periods, resulting in extended overall breeding timelines. Clutch and brood sizes did not vary between habitats, although urban eggs were smaller, narrower, and more elongated. Fledging success was significantly higher in urban nestboxes than in rural nestboxes. Most importantly, urban fledglings had compromised growth trajectories and poorer body conditions, indicating physiological and developmental costs of growing up in a city. Our results suggest that common mynas in anthropogenic habitats show wide variations in the timing of breeding and the growth trajectory of nestlings. These results enhance our understanding of avian life history plasticity in the face of rapid urbanization and offer a broad perspective on the evolutionary ecology of urban bird adaptation.