  Measuring the relation between star formation and galactic winds is
observationally difficult. In this work we make an indirect measurement of the
mass loading factor (the ratio between mass outflow rate and star formation
rate) in low-mass galaxies using a differential approach to modeling the
low-redshift evolution of the star-forming main sequence and mass-metallicity
relation. We use the SAGA (Satellites Around Galactic Analogs) background
galaxies, those spectra observed by the SAGA survey that are not associated
with the main SAGA host galaxies, to construct a sample of 11925
spectroscopically confirmed low-mass galaxies from $0.01\lesssim z \leq 0.21$
and measure a auroral line metallicity for 120 galaxies. The crux of the method
is to use the lowest redshift galaxies as the boundary condition of our model,
and to infer a mass-loading factor for the sample by comparing the expected
evolution of the low redshift reference sample in stellar mass, gas-phase
metallicity, and star formation rate against the observed properties of the
sample at higher redshift. We infer a mass-loading factor of $\eta_{\rm
m}=0.92^{+1.76}_{-0.74}$, which is in line with direct measurements of the
mass-loading factor from the literature despite the drastically different set
of assumptions needed for each approach. While our estimate of the mass-loading
factor is in good agreement with recent galaxy simulations that focus on
resolving the dynamics of the interstellar medium, it is smaller by over an
order of magnitude than the mass-loading factor produced by many contemporary
cosmological simulations.
