GWINNER, E. 1964. Untersuchungen iiber das Ausdrucksund Sozialverhalten des Kolkraben (Corvus corax corax L.). Z. Tierpsychol. 21:657-748. HEINRICH, B. 1988. Winter foraging at carcasses by three sympatric corvids, with emphasis on recruitment by the raven, Corvus corax. Behav. Ecol. Sociobiol. 23:141-156. HEINRICH, B., AND J. M. MARZLUzLU. 1991. Do Common Ravens yell because they want to attract others? Behav. Ecol. Sociobiol. 28:13-21. HUBER, B. 1988. Zur Sozialstruktur einer freilebenden Kolkrabenpopulation in der Schweiz. Ph.D.diss., Univ. Bern, Bern, Switzerland. KERTTU, M. E. 1973. Aging techniques for the Common Raven Corvus corax principalis Ridgway. M.Sc.thesis, Michigan Technical Univ., Houghton, MI. LIGON, J. D., AND J. L. WHITE. 1974. Molt and its timing in the Piiion Jay Gymnorhinus cyanocephalus. Condor 76:274-287. MAHRINGER, E. B. 1970. The population dynamics of the Common Raven (Corvus corax principalis Ridgway) on the Baraga Plains, L'Anse, Michigan. M.Sc.thesis, Michigan Tech. Univ., Houghton, MI. MARZLUF, J. M., AND B. HEINRICH. 1991. Foraging by Common Ravens in the presence and absence of territory holders: an experimental analysis of social foraging. Anim. Behav. 42:755-770.