  Both observations and simulations have shown strong evidence for highly
time-variable star formation in low-mass and/or high-redshift galaxies, which
has important observational implications because high-redshift galaxy samples
are rest-UV selected and therefore particularly sensitive to the recent star
formation. Using a suite of cosmological "zoom-in" simulations at $z>5$ from
the Feedback in Realistic Environments (FIRE) project, we examine the
implications of bursty star formation histories for observations of
high-redshift galaxies with JWST. We characterize how the galaxy observability
depends on the star formation history. We also investigate selection effects
due to bursty star formation on the physical properties measured, such as the
gas fraction, specific star formation rate, and metallicity. We find the
observability to be highly time-dependent for galaxies near the survey's
limiting flux due to the SFR variability: as the star formation rate
fluctuates, the same galaxy oscillates in and out of the observable sample. The
observable fraction $f_\mathrm{obs} = 50\%$ at $z \sim 7$ and $M_{\star} \sim
10^{8.5}$ to $10^{9}\,M_{\odot}$ for a JWST/NIRCam survey reaching a limiting
magnitude of $m^\mathrm{lim}_\mathrm{AB} \sim 29$-$30$, representative of
surveys such as JADES and CEERS. JWST-detectable galaxies near the survey limit
tend to have properties characteristic of galaxies in the bursty phase: on
average, they show approximately 2.5 times higher cold, dense gas fractions and
20 times higher specific star formation rates at a given stellar mass than
galaxies below the rest-UV detection threshold. Our study represents a first
step in quantifying selection effects and the associated biases due to bursty
star formation in studying high-redshift galaxy properties.
