Bird-Borne Video-Cameras Show That Seabird Movement Patterns Relate to Previously Unrevealed Proximate Environment, Not Prey

Abstract

The study of ecological and behavioral processes has been revolutionized in the last two decades with the rapid development of biologging-science. Recently, using image-capturing devices, some pilot studies demonstrated the potential of understanding marine vertebrate movement patterns in relation to their proximate, as opposed to remote sensed environmental contexts. Here, using miniaturized video cameras and GPS tracking recorders simultaneously, we show for the first time that information on the immediate visual surroundings of a foraging seabird, the Cape gannet, is fundamental in understanding the origins of its movement patterns. We found that movement patterns were related to specific stimuli which were mostly other predators such as gannets, dolphins or fishing boats. Contrary to a widely accepted idea, our data suggest that foraging seabirds are not directly looking for prey. Instead, they search for indicators of the presence of prey, the latter being targeted at the very last moment and at a very small scale. We demonstrate that movement patterns of foraging seabirds can be heavily driven by processes unobservable with conventional methodology. Except perhaps for large scale processes, local-enhancement seems to be the only ruling mechanism; this has profounds implications for ecosystem-based management of marine areas.

Mate similarity in foraging Kerguelen shags: a combined bio-logging and stable isotope investigation

“…Indeed, seabirds, including cormorants, are known to be able to use visual, tactile, and olfactive cues from their congeners for more efficient foraging (Ward & Zahavi 1973, Silverman et al 2004 as are other groups of animals (Galef & Wigmore 1983, Drapier et al 2002, White et al 2008). Furthermore, seabirds are able to use information transfer and depart the colony following the direction from which conspecifics are returning to the colony (Tremblay et al 2014). A transfer of information between paired birds would be facilitated by the temporal segregation in foraging between males and females, with males cueing on their partners' flight directions as they return from morning foraging trips and follow more similar bearings to their partners compared to other conspecifics (Tremblay et al 2014).…”

“…Furthermore, seabirds are able to use information transfer and depart the colony following the direction from which conspecifics are returning to the colony (Tremblay et al 2014). A transfer of information between paired birds would be facilitated by the temporal segregation in foraging between males and females, with males cueing on their partners' flight directions as they return from morning foraging trips and follow more similar bearings to their partners compared to other conspecifics (Tremblay et al 2014). Such similarity not only in bearings but also in foraging areas might also explain why mates tended to dive at more similar depths, as Kerguelen shags are benthic divers.…”

Relative importance of local enhancement as a search strategy for breeding seabirds: an experimental approach

“…dolphins, whales) in the study area (Davoren et al, 2010) and elsewhere (e.g. Camphuysen & Webb, 1999;Tremblay et al, 2014). Gannets did not respond more to the Gannet treatment relative to the Hotspot treatment, however, possibly because sitting, nonforaging gannet decoys alone may not reliably signal nearby prey.…”

“…Grunbaum & Veit, 2003) as well as observational studies (e.g. Thiebault, Mullers, Pistorius, & Meza-Torres et al, 2014Tremblay et al, 2014) indicate that seabirds have higher foraging success and/or expend less time/energy while searching if public information is used. For instance, cape gannets, Morus capensis, halve the time to first dive on foraging trips from the colony during the breeding season by responding to flying conspecifics either returning to or departing from the colony (Thiebault, Mullers, Pistorius, & Meza-Torres et al, 2014).…”

“…This suggests that competition among predators will not be important unless prey density in the study area becomes extremely low . In contrast, densities of predators above a particular threshold, specifically conspecifics, may be required for efficient foraging (Grunbaum & Veit, 2003;Tremblay et al, 2014), suggesting that Allee effects may be observed at the population level when predator densities drop below this threshold.…”