Capsule: Carbon dioxide (CO2) concentrations in the burrows of sand martins Riparia riparia increase with depth but have no detectable impact on fledging success.
Aims: To investigate whether burrow depth and CO2 concentrations influence reproductive success in sand martins.
Methods: We monitored two Sand Martin colonies along the River Lune, Lancashire (UK) to investigate the effect of burrow depth on reproductive success. We also measured CO2 levels in a sample of burrows to test whether burrow depth predicts CO2 concentration, and to test for a relationship between CO2 concentration and breeding success.
Results: Burrow depth was significantly correlated with fledging success, but the correlation was positive in first broods and negative in second broods. The highest CO2 concentration recorded was 73 650 ppm and the mean concentration across burrows was 31 757 ppm. However, while CO2 concentrations were positively correlated with burrow depth after controlling for the number and age of nestlings, they were not correlated with reproductive success.
Conclusion: There are reproductive costs associated with deeper burrows in second broods, but these could not be attributed to CO2 concentrations despite the exceptionally high levels recorded. This study highlights the need for further investigation into gas exchange and the potential impacts of, or adaptations to, CO2 accumulation in avian burrows.