In the below file, I wanted the three references to be cited as Inger et al 2006a, Inger et al 2006b and Inger et al 2006c. This answer seems to achieve what I want, but requires fiddling with the .bib file. Is there a way to achieve this outside of the .bib file?
\documentclass{article}
\usepackage[comma, sort&compress]{natbib}
\usepackage{filecontents}
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{IngerEtAl2006a,
title={Using daily ration models and stable isotope analysis to predict biomass depletion by herbivores},
author={Inger, Richard and Ruxton, Graeme D and Newton, Jason and Colhoun, Kendrew and Mackie, Kerry and Robinson, James A and Bearhop, Stuart},
journal={Journal of Applied Ecology},
volume={43},
number={5},
pages={1022--1030},
year={2006},
publisher={Wiley Online Library},
tag={}
}
@article{IngerEtAl2006b,
title={Prey choice affects the trade-off balance between predation and starvation in an avian herbivore},
author={Inger, Richard and Bearhop, Stuart and Robinson, James A and Ruxton, Graeme},
journal={Animal Behaviour},
volume={71},
number={7},
pages={1335--1341},
year={2006},
publisher={Elsevier}
}
@article{IngerEtAl2006c,
title={Temporal and intrapopulation variation in prey choice of wintering geese determined by stable isotope analysis},
author={Inger, Richard and Ruxton, Graeme D and Newton, Jason and Colhoun, Kendrew and Robinson, James A and Jackson, Andrew L and Bearhop, Stuart},
journal={Journal of Animal Ecology},
volume={75},
number={5},
pages={1190--1200},
year={2006},
publisher={Wiley Online Library}
}
\end{filecontents}
\begin{document}
\cite{IngerEtAl2006a}\\\\
\cite{IngerEtAl2006b}\\\\
\cite{IngerEtAl2006c}
\bibliographystyle{agsm}
\bibliography{\jobname}
\end{document}
biblatex