  The effect of stochasticity, in the form of Gaussian white noise, in a
predator-prey model with two distinct time-scales is presented. A supercritical
singular Hopf bifurcation yields a Type II excitability in the deterministic
model. We explore the effect of stochasticity in the excitable regime, leading
to dynamics that are not anticipated by its deterministic counterpart. The
stochastic model admits several kinds of noise-driven mixed-mode oscillations
which capture the intermediate dynamics between two cycles of population
outbreaks. Depending on the strength of noise, the prey population exhibits
intermediate to high-amplitude fluctuations (related to moderate or severe
outbreaks respectively). We classify these fluctuations as isolated or
intermittent or as clusters depending on their recurrences. We study the
distribution of the random variable $N$, representing the number of small
oscillations between successive spikes, as a function of the noise intensity
and the distance to the Hopf bifurcation. The distribution of $N$ is
"asymptotically geometric" with the corresponding parameter related to the
principal eigenvalue of a substochastic Markov chain. Finally, the stochastic
model is transformed into its "normal form" which is used to obtain an estimate
of the probability of repeated outbreaks.
