Comprehensively understanding the factors affecting physiology and fitness in urban wildlife requires concurrently considering multiple stressors.  To this end, we simultaneously assessed how metal pollution and proximity to roads affect body condition and telomere shortening between days 8 and 15 of age in nestling great tits (Parus major), a common urban bird.  We employed a repeated-measures sampling design to compare telomere shortening and body condition between nestlings from four urban study sites south of Antwerp, Belgium, which are located at different distances from a metal pollution point source.  In addition, we explored associations between metal exposure and telomere dynamics on the individual level by measuring blood concentrations of five metals/metalloids, of which lead, copper and zinc were present at concentrations about the limit of detection.  To assess whether roadway-associated stressors (e.g. noise and air pollution) might affect nestling condition and telomere shortening, we measured the proximity of nest boxes to roads.  Metal exposure was not associated with nestling telomere length or body condition, despite elevated blood lead concentrations close to a metal pollution source (mean ± SE = 0.270 ± 0.095 µg/g wet weight at the most polluted study site), suggesting that nestlings may have some capacity to detoxify metals.  However, nestlings from nest boxes near roads exhibited more telomere shortening between days 8 and 15 of age, and shorter telomeres at day 15. Nestlings in poorer condition also had shorter telomeres, but proximity to the road was unrelated to body condition.  Thus, nutritional stress is unlikely to mediate the relationship between proximity to roads and telomere length.  Rather, proximity to roads could have affected telomere shortening by exposing nestlings to air or noise pollution.  Our study highlights that traffic-related pollution, which is implicated in human health problems, might also affect urban wildlife.

This dataset contains the relative telomere lengths (RTL) of great tit nestlings from study sites exposed to different levels of metal pollution, measured using qPCR.  Raw crossing points (CPs) from the qPCR are also given.  GAPDH was used as a reference gene, and we used the following formula to calculate calibrator-normalized relative telomere length (RTL; amount of telomere sequence relative to GAPDH; T/S ratio):  RTL = E_T^{CtT(C)-CtT(S)} * E_R^{CtR(S)-CtR(C)}.  Additional variables in the data set are study site, distance from the road, nest box identity, clutch identity, year, mass, tarsus length and nestling sex, nestling age (8 or 15 days), and blood concentrations of metals (Pb, Zn, Ni, Cu, Cr).  The RunID is the identity of the qPCR reaction, and was controlled for in statistical analyses involving telomere length.

Outlying lead concencentrations were dropped from statistical analyses involving blood metal levels (outlier Lww2 column), and duplicate measurements on nestlings at the same age were also dropped (drop column).  Telomere measurements with CVs above 0.35 were dropped.