  Recent work by Levitan et al has expanded the long-term photometric database
for AM CVn stars. In particular, their outburst properties are well-correlated
with orbital period, and allow constraints to be placed on the secular mass
transfer rate between secondary and primary if one adopts the disk instability
model for the outbursts. We use the observed range of outbursting behavior for
AM CVn systems as a function of orbital period to place a constraint on mass
transfer rate versus orbital period P. We infer a rate ~5 x 10^{-9} Msun/yr
(P/1000 s)^{-5.2}. We show the functional form so obtained is consistent with
the recurrence time-orbital period relation found by Levitan et al using a
simple theory for the recurrence time. Also, we predict their steep dependence
of outburst duration on orbital period will flatten considerably once the
longer orbital period systems have more complete observations.
