VICARIOUS SAMPLING - THE USE OF PERSONAL AND PUBLIC INFORMATION BY STARLINGS FORAGING IN A SIMPLE PATCHY ENVIRONMENT

Group foragers may be able to assess patch quality more efficiently by paying attention to the sampling activities of conspecifics foraging in the same patch. In a previous field experiment, we showed that star lings foraging on patches of hidden food could use the successful fora ging activities of others to help them assess patch quality. In order to determine whether a starling could also use another individual's la ck of foraging success to assess and depart from empty patches more qu ickly, we carried out two experimental studies which compared the beha viour of captive starlings sampling artificial patches both when alone and when in pairs. Solitary starlings were first trained to assess pa tch quality in our experimental two-patch system, and were then tested on an empty patch both alone and with two types of partner bird. One partner sampled very few holes and thus provided a low amount of publi c information; the other sampled numerous holes and thus provided a hi gh amount of public information. In experiment I, we found no evidence of vicarious sampling. Subjects sampled a similar number of empty hol es when alone as when with the low and high information partners; thus they continued to rely on their own personal information to make thei r patch departure decisions. In experiment 2, we modified the experime ntal patches, increasing the ease with which a bird could watch anothe r's sampling activities, and increasing the difficulty of acquiring ac curate personal sampling information. This time, subjects apparently d id use public information, sampling fewer empty holes before departure when with the high-information partner than when with the low-informa tion partner, and sampling fewer holes when with the low-information p artner than when alone. We suggest that the degree to which personal a nd public information are used is likely to depend both on a forager's ability to remember where it has already sampled and on the type of e nvironment in which foraging takes place.