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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. June 2012 
Dawn Dusk 
FIG. 2. Average number of masked Veery songs and 
average number ol masking species for Veery song samples 
recorded at dawn and at dusk. Error bars represent standard 
errors; P-values represent results from two-tailed 
Student's /-tests. 
Wood Thrush masked lewer songs per sample (15 
masks in 4 samples), and the Ovenbird masked 
few songs per sample, but appeared in the greatest 
number of samples (28 masks in 1 1 samples). 
DISCUSSION 
Veeries tended to experience less acousti 
competition from other birds’ songs during th 
dusk chorus than during the dawn chorus. Mor 
Veery songs were masked and a larger number o 
species masked the Veery songs at dawn. Much o 
the masking was caused by three common specie 
at our site, all ol which produce songs that share 
wide frequency range with Veery song. On, 
species, the Wood Thrush, is closely related t« 
the Veery and has songs with similar spectra 
properttes (Dilger 1956, Borror 1964). The othe 
two species. Gray Catbird and Ovenbird. tend h 
sing loudly, at high amplitudes (KLB. JLH. an< 
KAS ’ P ers ' obs -)- We observed Veeries will 
tern tones near forest edges experienced high rate- 
of masking Irom Gray Catbirds, which sing nearly 
ontinuous bouts of song that varied widely in 
length. I he major,ty 0 f the territories that we 
sampled were not edge territories. These results 
represent the first empirical data documenting 
natural differences in acoustic competition at 
dawn and dusk. 
We do not know of any other studies that have 
compared hcterospecific acoustic competition dur¬ 
ing the dawn and dusk choruses, hut a number of 
studies have found species adjust the short-term 
timing of their vocalizations to avoid acoustic 
competition. Knapton (1987) found Eastern Mead¬ 
owlarks (, Sturrwlla magna) adjust the timing of 
their songs to avoid masking the songs of 
con specifics, and Brumm (2006) found Common 
Nightingales ( Luscinia megarhynchos) also avoid 
cd overlapping playback of recorded heterospecific 
songs. Ficken et al. (1974) reported Least Fly¬ 
catchers ( Empidonux minimus) and Red-eved 
Vireos ( Vi re o olivuceu.s) adjusted the timing of 
their songs to avoid overlapping each other. Popp 
et al, (1985) found several passerine species it) a 
Wisconsin forest community avoided overlapping 
songs ol other species more often than they would 
by chance. Ovenbirds regularly achieved this 
overlap reduction by singing just after the end of 
another bird's song. Planque and Slabbekoom 
(2008) found birds in a neotropical rainforest 
community that signaled in often-used frequency 
ranges overlapped each other’s songs less often 
than expected by chance. 
Our results indicate Veeries experience more 
acoustic competition at dawn than at dusk, and we 
hypothesize these birds may sing at dusk to 
compensate for their loss of efficiency in commu¬ 
nicating at dawn. Veeries and other thrushes may 
have evolved a pronounced dusk chorus partly to 
compensate lor the acoustical competitive disad¬ 
vantage caused by their complex song stmeture and 
thickly vegetated habitat. If this is tme. acoustic 
competition may represent one previously unstud¬ 
ied factor shaping the evolution of dusk singing bv 
the Veery and other dusk-chorusing species. 
ACKNOWLEDGMENTS 
We thank B. L Kuss and J. K. Kelly for help with 
spectrographic analysis, and E. C. Duke for help collecting 
some of the recordings. Wc thank D. A. Spector and an 
anonymous reviewer for help in improving the quality of 
the manuscript. This research was funded by National 
■Science Foundation (DEB 0746985) to KAS and a 
Research Experience for Undergraduates gran, I.DBI 
0552871) to Alan Berkowitz at the Cary Institute ol 
Ecosystems Studies distributed to JLH. Our methods were 
approved by the IACUC of Texas Tech University, protocol 
# 08047-02. 
