  Collective motion is abundant in nature, producing a vast amount of phenomena
which have been studied in recent years, including the landing of flocks of
birds. We investigate the collective decision making scenario where a flock of
birds decides the optimal time of landing in the absence of a global leader. We
introduce a simple phenomenological model in the spirit of the statistical
mechanics-based self-propelled particles (SPP-s) approach to interpret this
process. We expect that our model is applicable to a larger class of
spatiotemporal decision making situations than just the landing of flocks
(which process is used as a paradigmatic case). In the model birds are only
influenced by observable variables, like position and velocity. Heterogeneity
is introduced in the flock in terms of a depletion time after which a bird
feels increasing bias to move towards the ground. Our model demonstrates a
possible mechanism by which animals in a large group can arrive at an
egalitarian decision about the time of switching from one activity to another
in the absence of a leader. In particular, we show the existence of a
paradoxical effect where noise enhances the coherence of the landing process.
