Experimental manipulation of population density in a wild bird alters social structure but not patch discovery rate

Population density is a fundamental ecological feature influencing the opportunity for social encounters between individuals. Hence, density can impact various population processes such as social transmission. While the density dependence of disease spread has been studied extensively, we know little about how variation in density influences information transmission. If high densities lead to more social connections, information may spread more rapidly. Here, we experimentally manipulated local population density in great tits, Parus major, and investigated the effects on individuals' acquisition of information on novel food patches. We manipulated density by assigning individuals to either a high- or low-density treatment using automated bird feeders in the wild. We first show how our approach successfully led to changes in local population density. Next, we examine how the manipulation changed the local and individual social environment. At the local level, high-density locations resulted on average in denser and more clustered social networks compared to low-density locations. At the individual level, birds assigned to the high-density treatment had on average more social connections and more central network positions than birds in the low-density treatment. However, despite the effect on network structure, we found no evidence that the density manipulation influenced an individuals' likelihood, or speed, of locating novel food patches. Birds in the low-density treatment still spent a large proportion of time foraging at the high-density location. Thus, the manipulation did not lead to a strict segregation between birds of the different treatments, which may be one explanation for the absence of an effect on patch discovery.