1 Supplemental Data Environmental conditions in early life influence ageing rates in a wild population of red deer Daniel H. Nussey, Loeske E.B. Kruuk, Alison Morris & Tim H. Clutton-Brock Acknowledgements We are grateful to Scottish Natural Heritage and the Rum community for supporting our research on the Isle of Rum. This work is indebted to the fieldwork efforts of Fiona Guinness, Josephine Pemberton, Sean Morris and many research volunteers. We are also grateful to Josephine Pemberton, Tim Coulson, Kelly Moyes, Fanie Pelletier, Alastair Wilson, Sarah Reece, Julien Martin, Marco Festa-Bianchet, Jean-Michel Gaillard and two anonymous reviewers for their helpful comments and discussion. Research was funded by grants from NERC. Supplemental Experimental Procedures Study Population & Data Selection Criteria Red deer in the North Block of the Isle of Rum, Scotland, have been the subject of a long-term individual-based study that began in the early 1970s. Culling of deer within the North Block completely ceased in 1973, and the number of females in the study area increased almost three- fold in the following decade [S1, S2]. The population size reached carrying capacity during the mid-1980s and has fluctuated around 200 adult females since then [S3] (see Figure S1). Female red deer are highly philopatric and migration into or out of the North Block is rare [S1, S4]. Females conceive during the autumn rut (September – November) and give birth the following