Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior

Abstract

Group foraging contradicts classic ecological theory because intraspecific competition normally increases with aggregation. Hence, there should be evolutionary benefits to group foraging. The study of group foraging in the field remains challenging however, because of the large number of individuals involved and the remoteness of the interactions to the observer. Biologging represents a cost‐effective solution to these methodological issues. By deploying GPS and temperature–depth loggers on individuals over a period of several consecutive days, we investigated intraspecific foraging interactions in the Socotra cormorant Phalacrocorax nigrogularis, a threatened colonial seabird endemic to the Arabian Peninsula. In particular, we examined how closely birds from the same colony associated with each other spatially when they were at sea at the same time and the distance between foraging dives at different periods of the day. Results show that the position of different birds overlapped substantially, all birds targeting the same general foraging grounds throughout the day, likely following the same school of fish. There were as many as 44,500 birds within the foraging flock at sea at any time (50% of the colony), and flocking density was high, with distance between birds ranging from 8 to 1,380 m. Birds adopted a diving strategy maximizing time spent underwater relative to surface time, resulting in up to 72% of birds underwater in potential contact with prey at all times while foraging. Our data suggest that the benefits of group foraging outweigh the costs of intense aggregation in this seabird. Prey detection and information transmission are facilitated in large groups. Once discovered, shoaling prey are concentrated under the effect of the multitude. Fish school cohesiveness is then disorganized by continuous attacks of diving birds to facilitate prey capture. Decreasing population size could pose a risk to the persistence of threatened seabirds where group size is important for foraging success.

Evidence of sociality in the timing and location of foraging in a colonial seabird

“…However, previous studies examining the potential transmission of information at colonies, through direct between-pair signalling [9] and colony co-departures, have produced mixed results (e.g. [9][10][11][12]) and generally focus on either behaviours at the colony or foraging site separately (but see [9,13,14]), and so the link between these behaviours remains unresolved. Notably, without the knowledge of subsequent foraging locations and availability of & 2018 The Author(s) Published by the Royal Society.…”

Raking the ocean surface: new patterns of coordinated motion in seabirds

“…Underwater movements of penguins revealed synchronised foraging trips and dives (Tremblay and Cherel , Takahashi et al ), presumably allowed by constant visual contact. Synchronisation was also observed in departure times of foraging Australasian gannets ( Morus serrator ) from the near‐colony raft (Machovsky‐Capuska et al ), in sooty shearwaters ( Puffinus griseus ) flights to join feeding heterospecifics (Hoffman et al ), and in Socotra cormorants ( Phalacrocorax nigrogularis ) foraging trips (Cook et al ). However, rakes involved both synchronisation and coordination, and such patterns have never been observed at scales reaching several kilometres.…”

“…Various seabird species are known to forage in groups (Takahashi et al , Weimerskirch et al , Thiebault et al , Sutton et al , Cook et al ) or to temporarily associate in multi‐specific assemblages of predators jointly exploiting resource patches (Au and Pitman , Harrison et al , Clua and Grosvalet , Hebshi et al , Veit and Harrison ). In addition to shortening foraging search time (Pitcher et al ), group foraging has been suggested to enhance feeding rate and decrease its variance (Clark and Mangel , ), as well as to improve patch quality assessment (Brown ) by the means of information sharing between individuals.…”

Consistent sociality but flexible social associations across temporal and spatial foraging contexts in a colonial breeder

“…Previous studies in seabirds have often inferred that joint departure from the colony represents social information transmission between individuals (e.g. Weimerskirch et al 2010; Racine et al 2012) and recent works have demonstrated that individuals co‐departing together can share foraging areas (Cook et al 2017; Sutton et al 2017; Jones et al 2018). Our study demonstrates that although social associations formed across four foraging contexts, there was only small carry‐over in specific associations across contexts.…”

“…Previous studies have shown seabirds can form groups at the colony during outward travel (Daniel et al 2007; Weimerskirch et al 2010; Machovsky‐Capuska et al 2013; Jones et al 2018) and during commuting travel between colony and foraging locations (Berlincourt & Arnould 2014; Tremblay et al 2014; Thiebault et al 2014a), which can allow the colony to act as a centre for foraging information, and can lead to individuals engaging in following behaviour (Harel et al 2017). At sea, seabirds are also known to form foraging aggregations (Coulson 2001; Evans et al 2015; Cook et al 2017), and evidence from experimental and modelling approaches have demonstrated that these aggregations can provide social information by attracting individuals to a foraging locations through the observation of other foraging individuals (local enhancement; Buckley 1997; Thiebault et al 2014b; Bairos‐Novak et al 2015; Boyd et al 2016). However, it remains unclear to what extent these aggregations indicate active social choices in comparison to patterns emerging due to shared space use associated with a clumped resource.…”