  The classical model of massive-star mechanical feedback is based on effects
at solar metallicity (Zsun), yet feedback parameters are very different at low
metallicity. Metal-poor stellar winds are much weaker, and more massive
supernova progenitors likely collapse directly to black holes without
exploding. Thus, for ~0.4 Zsun we find reductions in the total integrated
mechanical energy and momentum of ~40% and 75%, respectively, compared to
values classically expected at solar metallicity. But in particular, these
changes effectively delay the onset of mechanical feedback until ages of ~10
Myr. Feedback from high-mass X-ray binaries could slightly increase mechanical
luminosity between ages 5-10 Myr, but it is stochastic and unlikely to be
significant on this timescale. Stellar dynamical mechanisms remove most massive
stars from clusters well before 10 Myr, which would further promote this
effect; this process is exacerbated by gas retention implied by weak feedback.
Delayed mechanical feedback implies that radiation feedback therefore dominates
at early ages, which is consistent with the observed absence of superwinds in
some extreme starbursts. This scenario may lead to higher star-formation
efficiencies, multiple stellar populations in clusters, and higher Lyman
continuum escape. This could explain the giant star-forming complexes in
metal-poor galaxies and the small sizes of OB superbubble shells relative to
their inferred ages. It could also drive modest effects on galactic chemical
evolution, including on oxygen abundances. Thus, delayed low-metallicity
mechanical feedback may have broad implications, including for early cosmic
epochs.
