Many rodent species exhibit periodic fluctuations in population abundance.This can have important consequences for processes known to be influenced by population density,such as dispersal,territoriality,reproduction and disease transmission.Evidence for the role of density has been almost uniquely gathered from observational field data,which makes it difficult to accurately detect causality or to quantify the effect of density.Using semi-natural field enclosures of 0.5ha,we measured contact rates in Natal multimammate mice,a species known for its extreme population fluctuations,at a wide range of densities (10/ha – 280/ha) .Contact rates increased in a density-dependent fashion,not linearly as may be expected but sigmoidally,reaching a maximum level at 160/ha.There was considerable individual heterogeneity in the number of contacts and in the degree of connectedness.This quantified relationship between density and contacts can be used to inform models of disease transmission or population dynamics,and can improve our interpretation of field data.