Seabird acoustic communication at sea: a new perspective using bio-logging devices

Abstract

Most seabirds are very noisy at their breeding colonies, when aggregated in high densities. Calls are used for individual recognition and also emitted during agonistic interactions. When at sea, many seabirds aggregate over patchily distributed resources and may benefit from foraging in groups. Because these aggregations are so common, it raises the question of whether seabirds use acoustic communication when foraging at sea? We deployed video-cameras with built in microphones on 36 Cape gannets (Morus capensis) during the breeding season of 2010–2011 at Bird Island (Algoa Bay, South Africa) to study their foraging behaviour and vocal activity at sea. Group formation was derived from the camera footage. During ~42 h, calls were recorded on 72 occasions from 16 birds. Vocalization exclusively took place in the presence of conspecifics, and mostly in feeding aggregations (81% of the vocalizations). From the observation of the behaviours of birds associated with the emission of calls, we suggest that the calls were emitted to avoid collisions between birds. Our observations show that at least some seabirds use acoustic communication when foraging at sea. These findings open up new perspectives for research on seabirds foraging ecology and their interactions at sea.

At sea vocal repertoire of a foraging seabird

“…Within each context, calls were specific to individuals which can be explained by differences in anatomy based on the source‐filter theory (Fant , Fitch ). Different individuals may have vocal tracts of slightly different sizes including their syrinx, the ‘source’ from which they emit calls (Greenewalt , Suthers and Zollinger , Riede and Goller , Fitch and Suthers ). Accordingly, the F0 was the variable with the highest PIC value in contexts FLY and DIV (Table 2) and the variable of most importance to correctly predict the emitter of the call with the RF (Fig.…”

“…As a consequence, species from all seabird orders commonly gather at sites where prey resources are concentrated, most often in multi-species associations (Siegfried et al 1975, Hoffman et al 1981, Harrison et al 1991, Camphuysen and Webb 1999, Clua and Grosvalet 2001. In this context, individuals may benefit from group foraging (Ryan et al 2012, Lett et al 2014, Thiebault et al 2015, McInnes et al 2017) and use both visual and acoustic cues (Thiebault et al 2014b(Thiebault et al , 2016. Despite numerous descriptions of seabird aggregations (mainly from boat observations), studies addressing the mechanisms involved in their social interactions at sea have long been constrained by technical limitations.…”

“…It is only recently that studies quantifying seabirds interactions at sea have gained impetus thanks to the miniaturisation of image recording devices in particular (Berlincourt and Arnould 2014, McInnes et al 2017. Although visual observation of in-situ foraging seabirds have greatly improved interpretation of remote movement data, the study of their vocal communication at sea has only very recently started (Thiebault et al 2016, Choi et al 2017.…”

“…Here, we aimed to study the acoustic structure of calls emitted at sea by a seabird. We chose the Cape gannet Morus capensis because of the known importance of social interactions in the foraging strategies of this particular species (Thiebault et al 2014a(Thiebault et al , b, 2015(Thiebault et al , 2016. The Cape gannet is a monomorphic seabird endemic to southern Africa with adults breeding in dense colonies (Nelson 2005).…”

“…Once aggregated at a fish school, they benefit from the quasi-synchronisation of attacks by the group of predators to capture prey (Thiebault et al 2015). During those foraging activities, we know that Cape gannets do emit calls, but no detailed acoustic analysis could previously be done due to the poor quality of the sound recorded (Thiebault et al 2016). In particular, we do not know if the calls emitted in different behavioural contexts have different acoustic structures.…”