Large roosting concentrations of birds can be noisy, and the associated droppings can be a nuisance because of the objectionable odor and mess. In addition, birds may carry and transmit diseases to livestock and humans. Collections of droppings may provide a medium for bacterial and fungal growth that could pose a potential public health problem. Birds should be dispersed or controlled when they form large concentrations near human habitations and are judged to pose a threat to public health or livestock. Concentrations of birds that do not threaten human health or agriculture are usually better left undisturbed.