Social behaviourSocial behaviour

Social behaviour

As with all other terns (Cabot and Nisbet 2013), Australian Fairy Terns are gregarious, gathering together at roost sites both during and outside the breeding season (Dunlop 2018). In Western Australia, night roosts are generally located on open shoreline features such as sandspits, away from vegetation cover and predators (Dunlop 2018). Some are only occupied during the arrival period whilst others are occupied for most of the breeding season. These roosts may contain birds at a range

of ages with the composition changing as the season progresses (Dunlop 2018). Night roosts may include pre- and post-breeding experienced adults, individuals entering their first breeding season, non-breeding individuals in their first summer, and fledglings (Dunlop 2018; J.N. Dunlop pers. obs.).

The social behaviour associated with colony site selection and establishment has not been investigated in Australian Fairy Terns, probably because it is hard to predict when and where it will occur (Dunlop 2018). In other terns that do not have inter-annual

nest-site fidelity, courting flocks of reproductively advanced, nuptial plumaged birds commonly occur adjacent to potential colony sites (e.g. Crested Tern - Dunlop 1987, Little Terns - Cramp et al. 1985, Sooty Tern - Ashmole 1963, and J.N. Dunlop pers. obs.). In Western Australia, ‘clubs’ are social roosts that are occupied by birds in breeding condition, have nuptial plumage, are courting and are ready to breed. Here pair bonds form or reform and these clubs are usually in close proximity to the breeding site.

These areas are critical to the social ecology of the species. Terns in these pre-breeding flocks are typically engaged in bouts of aerial courtship ‘social flights’ and ground displays or parades at diurnal club sites (Cabot and Nisbet 2013). Pairs form or re-form in these flocks and paired courtship displays frequently follow bouts of group behaviour.

In Western Australia, the timing of colony formation and egg-laying is likely dictated by food availability, with colonies forming close to areas of high food abundance (Dunlop 1987). Colonies may occur at the same general location for a series of seasons and then shift (Dunlop 2018). Some observations indicate that a ‘neighbourhood’ of

breeding terns return to the breeding site used in the previous year during the ‘clubbing’ phase but may then move in a coordinated way to a fresh location (Dunlop 1987, Sooty Tern - J.N. Dunlop pers. obs.). This behavioural pattern may assist in maintaining pair bonds together with providing the opportunity to synchronise timely breeding with neighbours of similar age/experience or quality. Younger, less experienced terns tend

to lag in their reproductive cycle, lay later outside the peak foraging window and, as a consequence, have reduced breeding success compared to more experienced pairs (Dunlop 2018).