Mageretal • LOONS SIGNAL HIGH AGGRESSION WITH LONGER YODELS 
79 
open water that would favor this means of honest 
communication of aggressive motivation. 
ACKNOWLEDGMENTS 
Parts of this manuscript were presented as partial 
Liniment of requirements of J. N. Mager's Doctor of 
Philosophy degree, in agreement with guidelines of IACUC 
approval 97-12-02 at Cornell University. Support was 
provided by Cornell University (Cornell Laboratory of 
Ornithology Walter Benning Fellowship, Department of 
N'eurobtology and Behavior Student Research Grant. Edna 
Bailey Suzman Fellowship. Kieckhefcr Adirondack pel 
owship. Local Sigma Xi Grunts-in-Aid-of-Research Grant. 
University Travel Gram), the Sigurd Olson Environmental 
Institute Loon Research Award, ihe Denison University 
Visiting Scholar Program, and the Ohio Northern l Jnivcrsity 
F.iculty Summer Research Grant. We thank A. A Dhondt. H. 
K. Reeve, and S. L. Vehrencamp for constructive recom¬ 
mendations in study design and manuscript preparation, 
kareu Grace-Martin and F. M. Vcrmcylcn lor statistical 
consulting, A. R. Lindsay. M. W. Meyer for assistance, the 
many held assistants for their hard work, and private 
limdown «S for access to lakes, encouragement, and support. 
LITERATURE CITED 
'riMAXN. J. 1974. Observational study of behavior: 
sampling methods. Behaviour 49: 227-267. 
WEBV, u. M. AND S. M. Redpath. 1997. Indicators of 
"tale quality in the hoots of Tawny Owls (Arm 
'Him Journal of Raptor Research 31: 65-70. 
Hi!'!. | | 9 gg 7 |, e behavioural biology of aggression, 
-amlifidgeUniversity Press. Cambridge. United Kingdom. 
•OrivUiw. W. E. 1979. The function of variations in the 
oculizations of the Common Loon (Gavia immer). 
Dissertation. Tufts University. Boston. Massachusetts. 
IJSA, 
; ^ 1 kv ,J. W. and S. L. Viiiupncami’, I'>98. Principles 
1,1 animal communication. Simmer Associates Inc.. 
Sunderland, Massachusetts, USA. 
' ,,f1 ‘ M. S. and W. A. Searcy . 1991. Acoustical 
WTimunication of aggressive intentions by territorial 
"'ale Bobolinks. Behavioral Ecology 2: 319-326. 
J '«tt,STEEN. T„ p. k. McGregor. J. Uni t and. J. A. 
foHivs. and s. B. Petersen. 1997. The signal 
’“nction of overlapping singing in male Robins. 
Animal Behaviour 53: 249-256. 
• IIST . M. and O. LEIMAR. 19X3. Evolution of fighting 
Nhaviour: decision rules and assessment of relative 
'length. Journal of Theoretical Biology 102: 3S7-4I0. 
'■wist, M. and O. Lf.imak. 19X7. Evolution of lighting 
behaviour: the effect of variation in resource value. 
Journal of Theoretical Biology 127- 187-205. 
>INs - P. J AND D. V. C. WKSELOH. 1999. Little Gull 
U-arus mbiutus). The birds of North America, 
dumber 428. 
llRr, ;P L. AND M. Enquis-1 .2001. Threat display in birds. 
Canadian Journal of Zoology 79: 931 -942. 
Jow ®ON, M. 2002. Individual growth analysis using PROC 
MIXED. Paper 253-27 in Proceedings of the twenty- 
seventh annual SAS users group international confer¬ 
ence. SAS Institute Inc.. Cary, North Carolina, USA. 
Johns roNL. R. A. 1996. Multiple displays in animal commu¬ 
nication: 'backup signals’ and ’multiple messages.’ 
Philosophical Transactions of (he Royal Society of 
London, Series B 351:329 338 
Kkoodsma. D. E. 1989. Suggested experimental designs 
for song playbacks. Animal Behaviour 37 600-609. 
I.AMISRI.CIIis. M. ANLJ A. A. DHONDT. 1986. Male quality, 
reproduction, and survival in the Great Tit ( Pants major). 
Behavioural Ecology and Sociobiology 19: 57-64. 
LamBRLCIITS, M. and A. A. DHONril. 1987. Differences in 
singing performance between male Great Tits. Ardea 
75; 43-52. 
Lanc.i,mann, U., J. P. Tavares. T. M. Peake, and P. K. 
McGregor. 2000. Response of Great Tits to escalat¬ 
ing patterns of playback. Behaviour 137: 451—471. 
Li Prf.li. C. G.. m. D Hauser, and D. B. Moody. 2002. 
Discrete or graded variation within rhesus monkey 
screams? Phychophysicai experiments on classifica¬ 
tion. Animal Behaviour 63: 47-62. 
Mag HR. J. N. 1995. A comparison of the time-activity 
budgets of breeding mule and female Common Loons 
(Gavid immer). Thesis. Miami University. Oxford, 
Ohio, USA. 
MAGER, j. N. AND c. Walcott. 2007. Structural and 
contextual characteristics of territorial “yodels” given 
by male Common Loons (Gavia immer ) in northern 
Wisconsin. Passenger Pigeon 69: 327-337. 
Magi r J. N. C. WALCOTT, and W. H. Piper. 2007a. Male 
Common Loons. Gavia immer. communicate body 
mass and condition through dominant frequencies of 
territorial yodels. Animal Behaviour 73: 683-690. 
Mager J. N. C. Walcott, and W. 11. Piher. 2007b. Nest 
platforms increase aggressive behavior in Common 
Loons. Naturwissenschaften 95: 141-147. 
Mager .1. N, C. Walcott, and W. H Pih-.r. 2010. 
Common Loons can differentiate yodels ol neighbor¬ 
ing and non-nbighboring conspccitics. Journal ol Field 
Ornithology 81: 392-401. 
MARTIN. P. and P. Bateson. 1993. Measuring behaviour: 
an introductory guide. Second Edition. Cambridge 
University Press. Cambridge. United Kingdom. 
Martin- Vi valdi. M.. J. J. Palomino, and M. Soler. 
■>004. Strophe length in spontaneous songs predicts 
male response to playback in the Hoopoe (Upupa 
epops). Ethology 110: 351-362. 
Mayn ard Smith. J. 1982. Do animals convey information 
about their intentions? Journal of I heoretical Biology 
97: 1-5. 
McIntyre. J. W. 1988. The Common Loon: spirit of 
northern lakes. University of Minnesota Press. Min¬ 
neapolis, LISA. 
Mowbray, T. B.. C. R. Ely. J. S. Sedjnger, and R. E. 
Trost. 2002. Canada Goose (Bran!a canadensis). The 
birds of North America. Number 682. 
Morion. H. S. 1977. On the occurrence and significance of 
motivation-structural rules in some bird and mammal 
sounds. American Naturalist 111: 855-869. 
Morton, E. S. 1982. Grading, discreteness, redundancy, 
and motivation-structural rules in some bird and 
