Templeton, C.N., E. Greene and K. Davis, 2005.  Allometry of alarm calls:  Black-capped Chickadees encode information about predator size.  Science 308: 1934 - 1937. Templeton, C.N. and E. Greene, 2007.  Nuthatches eavesdrop on variations in heterospecific chickadee mobbing alarm calls.  Proc. Natl. Acad. Sci. 104: 5479-5482.