The vocal and homing behaviour of the Manx shearwater Puffinus puffinus with additional studies on other Procellariiformes
The marine birds comprising the order Procellariiformes are an ancient and diverse assemblage. A large proportion are both nocturnal and burrow-nesting at their breeding colonies, where in sharp contrast to their behaviour at sea, they are highly vociferous. Virtually nothing is known regarding the adaptive features of this process. Various aspects of vocal behaviour have therefore been investigated from 1981 to 1983 for seven species at breeding stations in both the boreal and sub-tropical North Atlantic Ocean. In addition, the problem of how these birds return to their correct burrows at night has been considered. A detailed study was conducted on the Manx Shearwater Puffinus puffinus. Various approaches showed that immatures contribute most to the calling heard. Males establish and defend burrows, but both sexes partake in aerial calling. Calling at ground level serves both sexual and territorial functions, whereas aerial calling is probably mainly concerned with sexual advertisement. Some males are more silent in flight than others. These probably represent birds as yet without burrows, perhaps the youngest age classes. Flighting activity probably expedites the acquisition of burrows and mates in these birds which are awkward on land, and aerial calling probably improves signalling efficiency in attracting mates. Six other species (Bulweria bulwerii, Calonectris diomedea, Puffinus assimilis, Hydrobates pelagicus, Oceanodroma castro, Pelagodroma marina) were studied. As with Puffinus puffinus, sexual differences in voice exist for all except Bulweria and Pelagodroma, which also lack aerial calls. Thus a functional link exists between flight calls and their sexual divergence. Selection probably favours such divergence in species where males leave burrows to display in flight; the sexual identity of those species whose males do not is unambiguous as they remain in burrows and call. The calls of Puffinus puffinus and Hydrobates pelagicus were compared at local and regional levels. Divergence exists between but not within islands. Vocal drift in Puffinus puffinus is also apparent after several years. The calls of the nocturnal Procellariiformes are reviewed and discussed in relation to their systematics. The potential use of calls in petrel systematics is also evaluated and shown to be useful. Observations on Puffinus puffinus showed that olfactory and auditory cues are not used for burrow homing. Experiments also confirmed this, and point to sufficient visual development in this species, although other senses may be emphasised in different ecological situations.