76 
THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. I. March 2012 
of F clch' oer S !!= n „“, mbe ;m T?" ^ C ° mmon L °° ns * ” cial “»««■ Gray bats reprcS en, number 
or crouch yodels per event and black bars represent number of ‘vulture' yodels per event. 
of seasons an individual was observed = 3.7 ± 0.2 
median = 3 seasons) during 3,900 hrs of 
observation covered by our 6-year study. The 
number of prospecting loons flying over territories 
varied significantly with each territory (F 5M3I = 
1.718, P = 0.0051), but the frequency of distant 
intrusions (F 56 , 15 , = 1.505, P = 0.0268), ap¬ 
proaches (F 5615 | = 0.862, P = 0.7349) social 
gatherings (F S6 , J51 = 1.316, P = 0.0975), and 
aggressive chases/fights (F 5()il5 , = 1.202, P = 
0.1914) did not vary with territory. Intrusions that 
involved the close approach of the intruder without 
a social gathering occurred rarely; consequently, 
we report mean yodeling responses by males to 
these types of intrusions, but omit them from 
repeated-measures analyses of vodeling rates and 
number of repeat phrases given with stage of 
territorial intrusion. None of the contests resulted in 
eviction of territorial males. 
we observed 1,495 yodels from 58 banded m 
(mean ± SD; 13 ± I yodels recorded/individ 
year, range = 1-51). Forty-eighl of the 58 m; 
yodeled in al least two of the five social com, 
between 2002 and 2007; few gave yodels in all f 
Pooling all yodels from all males, males yotk 
primarily at conspoeiRcn (87.5% of all yodels) 
also yodeled al humans (10.8%). and Bald Eat 
he tT“ '* mac ‘ ph “ lu - , > d-7%). We obser 
siom T' S i°', ni " in8 infn -‘‘' ucnl in, 
territorial in^o, 48 0^561 
years). n,e frequency (# yodelsfoccurrenee) ma 
yodeled at conspecifics was related to the extent 
of intrusion (Friedman’s ANOVA f = 25.394.n 
= males, df = 3, P < 0.0001; Fig. 3). Males 
gave significantly more yodels when intruders 
landed on the territory than when intruders flew 
over the territory (Wilcoxon Z = 2.99. P = 
0.0028). and gave progressively fewer yodels per 
social gathering (Wilcoxon Z = 2.92. P = 
0.0035). However, male vodeling rate did not 
decrease as social gatherings escalated into chases 
or fights (Wilcoxon Z = 0.62. P = 0.54). Close 
intrusions that did not lead to social gatherings 
rarely occurred, but the likelihood that a resident 
nude would yodel was lowest (14.3% of all such 
occurrences) during this situation, implying some 
signal, or assessment of lower threat, associated 
with the intruding loon. 
Males gave most calls as ‘crouch’ yodels (94% 
°l given), but only gave crouch yodels at 
flyovers, distant intruders, and close intruders that 
did not escalate into social gatherings. Males gave 
more 'vulture-posture’ yodels when territorial 
contests escalated; 10.1 % of all calls given during 
social gatherings were crouch yodels, but 678 f 
of all yodels given during physical chases, and/or 
fights were vulture-posture yodels (Fig. 3). Male' 
(/i ' 25) observed yodel ing in both the crouch and 
vulture postures during a given vear gave yodels 
with more repeat phrases when in the vulture- 
posture (X ± SE = 4.95 ± 0.40) than in the 
crouch-posture (3.72 ± 0.26; paired l = 3.10. 
df - 24, P = 0.0049). Intruders rarely yodeled on 
territories of residents (130 yodels in the 6 years 
