Data from: Urban environment shortens telomere length in nestling great tits, Parus major

Urban environments are expanding rapidly, and with urbanization come both challenges and opportunities for wildlife. Challenges include combating the anthropogenic disturbances such as light-, noise- and air pollution and lower availability of natural food sources. The benefits are for many species the great availability of anthropogenic food sources, breeding boxes, and warmer temperatures. Thus, depending on the context, urbanization can have both positive and negative effects on fitness related traits. It is well-known that early-life environmental conditions can have life-long implications on fitness, however, little is known about development in urban environments. We reciprocally cross-fostered urban and rural nestling great tits (Parus major L.) to study how growing up in an urban vs. rural habitat affected telomere length (TL) - a suggested biomarker of longevity. We show, for the first time, that growing up in an urban environment significantly shortens TL, independently of natal origin (i.e. urban or rural) and also that TL is maintained better in the rural forest. This implies that the urban environment imposes a challenge to developing chicks, with potential irreversible effects on life span.