How does the presence of a conspecific individual change the behavioral game that a predator plays with its prey?

Social behaviour and foraging success of little egrets (Egretta garzetta)

Intraspecific interactions among predators can change the game between a predator and its prey. Individuals of different size or sex can differ in their responses to conspecific competitors. We studied intraspecific interactions among pairs of little egrets (Egretta garzetta) while foraging on responsive prey (comet goldfish, Carassius auratus). Testing little egrets in an artificial patchy environment both singly and while engaged in social forging in pairs (male & female) at two prey densities, allowed us to explore individual differences in foraging success. We found sexual dimorphism with males being bigger and more aggressive than females. However, female foraging success was positively affected by the time they spent foraging with a conspecific male, suggesting they might be able to mitigate male aggressiveness with an indirect positive interaction. Despite the presence of direct interactions between individuals in the pair, egret foraging success was not affected by such interactions, nor by prey density. Our results demonstrate the importance of sex and an individual's ability to adjust its social behaviour based on the behaviour of others in this predator-prey foraging game.

Neighborhood effects in mixed-species flocks affect foraging efficiency of intermediate and little egrets

Birds aggregate for various survival needs, and ardeids form both conspecific and mixed-species flocks. However, it remains unclear whether and how ardeids' foraging while joining a flock is affected differently in conspecific versus mixed-species flocks. We studied egret flocks in southwestern Taiwan to assess the flock size and neighborhood effects on flock formation and foraging performance of egrets by examining landing tendencies and expelling behaviors of Little (Egretta garzetta) and Intermediate (E. intermedia) egrets, and assessing strike rates, strike efficiency, and intake rates of singles and egrets in conspecific and mixed-species flocks. We found no evidence of non-random landings to mixed-species flocks by either species, but egrets showed a trend of landing closer to conspecifics when conspecifics represented lower proportions in flocks. Intermediate Egrets displayed expelling behavior more frequently. Expelling by earlier arrived egrets interrupted subsequent flock formation on 45.2 % occasions, but was not affected by egrets' foraging performance. Solitary Little Egrets had higher strike and fish intake rates, but lower strike efficiency, than solitary Intermediate Egrets, whereas their biomass intake rates were similar. Strike and fish intake rates increased in flocks compared to singles in both species, but declined for Little Egrets as flocks increased from medium (11-30 birds) to large sizes (> 30). Intermediate Egrets had higher strike, fish intake, and biomass intake rates, but Little Egrets had lowered strike efficiency and fish- and biomass-intake rates, when near each other than when near conspecifics. Overall, Intermediate Egrets in mixed-species flocks improved foraging efficiency and food intakes by neighborhood effects at costs of reduced foraging efficiency to Little Egrets. The variation in landing tendency over flock compositions suggests potential interactions of the neighborhood effect with egrets' conspecific attraction.

Time to revisit? A predator's previous successes and failures in prey capture determine its return time to patches

In a heterogeneous environment containing multiple patches that may deplete and renew, a forager should be able to detect the quality of food resources within and among patches and choose to exploit them to best maximize returns. From the predator's perspective, the behavioral responses of the prey in a patch will be perceived as depletion when they retreat to refuge and renewal when they reemerge. A predator encountering responsive prey should manage predation risk, and thus behavioral resource depression, by optimally timing its return time to the patch based on prey behavior. We evaluated the foraging decisions of a predator that encountered patches differing in size of the refuge and prey density. We used little egrets and goldfish as predators and prey in an environment that contained three patches (pools). We manipulated prey density and refuge size and availability (using covers) and observed predator foraging behavior. When the egret had previously caught a fish it did not discriminate between the pools, and the return time was similar for all cover types. The fish densities also did not affect the egret decisions to return to pools. However, when it failed to catch fish, it returned sooner to the pool containing the small cover than the larger one. Additionally, after failing to catch fish in patches containing the highest prey density, the egrets subsequently preferred to return to such patches sooner. We show experimentally that previous failures influence the foraging decisions of a predator choosing how quickly to return to a previously visited patch.