Belinsky et a!. • ACOUSTIC COMPETITION IN VEF.RIES 
267 
FIG. I. Sound spectrograms of three Vecry songs: one 
unmasked (A), one masked by a Black-capped Chickadee 
(B), and one masked hy an Ovcnbird (C). 
chose this amplitude threshold to mimic the 
experience of a hypothetical receiver. We decided 
that if a masking vocalization was below 75 db, it 
was not sufficiently loud to truly disrupt commu¬ 
nication between the singer and hypothetical 
receiver (the recordist). This threshold should be 
considered arbitrary as choosing a consistent 
threshold for ruling out soft/distant vocalizations 
was the primary goal. We attempted to identify 
the species of bird masking each masked Veery 
song. We calculated the mean number of masks 
occurring among the 34 dawn 10-song samples 
and compared it with the mean number occurring 
in the 34 dusk samples. We also compared the 
mean number of different species masking in the 
dawn and dusk song samples. We used JMP 5.0 
software for Mac (SAS Institute Inc. 2004) lo 
conduct two-tailed Student's /-tests. 
RESULTS 
The 68. 10-song segments were 61 ±2.8 sec 
long (mean ± SE). The length of the 10-song 
segments did not differ between the dawn and dusk 
recordings, indicating that singing rate and/or song 
TABLE I. Number of Vecry songs masked by all 
unidentified and identified species at dawn and dusk. 
Identified species include: Gray Catbird. Ovcnbird. Wood 
Thrush. American Robin, Tufted Titmouse ( Baeolophus 
hiculvr ), Red-eyed Vireo. Common Ycllowthroat ( Geothlvpis 
irichcis). Red-bellied Woodpecker ( Melanerpes carolinus). 
Black-capped Chickadee i Puerile citiiccipillus). Blue-headed 
Vireo (Vireo solitarius). Barred Owl (S/m voria). and Rose- 
breasted Grosbeak ( Pheucticns liubviciaims). 
Masking species 
Dawn songs 
masked 
Dusk songs 
masked 
Unidentified 
10 
17 
Gray Calbird 
20 
6 
Ovenbird 
16 
8 
Wood Thrush 
11 
4 
American Robin 
3 
5 
Tufted Titmouse 
4 
2 
Red-eyed Vireo 
6 
0 
Common Yellowthroat 
1 
2 
Red-bellied Woodpecker 
2 
1 
Black-capped Chickadee 
2 
0 
Blue-headed Vireo 
1 
0 
Barred Owl 
I 
0 
Rose-breasted Grosbeak 
1 
0 
length did not differ between our samples (dawn = 
60 ± 2.8 sec, dusk = 59 ± 2.8 sec: Student’s /: n — 
34, 1 = 0.19, P = 0.86). 
One hundred and twenty (17.6%) of the 680 
Veery songs we recorded were masked by another 
species' song. Veery songs were masked 2.4 ± 
0.4 times per 10 songs at dawn and 1.2 ± 0.4 
times per 10 songs at dusk (Table 1). Veeries 
experienced more acoustic competition at dawn 
than at dusk and. although this difference was 
marginally significant (Student’s /: n = 34, / = 
2.0. P = 0.05). the effect size was just below the 
cut-off for medium level (Cohen’s d - 0.49. 
medium effect si/e >0.5). Significantly more 
species contributed lo masking at dawn than dusk 
(Student’s /: // = 34, / = 3.1, P = 0.003), and this 
effect size was medium (Cohen's d - 0.75. large 
effect size >0.8). 
At least 12 species masked the Veery songs in 
our sample (Table I). All 12 species masked at 
dawn, but only seven of these masked at dusk and 
no species masked only at dusk (Table I). The 
species that masked Veery songs most commonly 
in both dawn and dusk samples were Gray Catbird 
(Dumetella carolinensis), Ovenbird. and Wood 
Thrush. The Gray Catbird masked many or all of 
the Veery' songs in the recordings in which it 
appeared (26 masks in 4 samples). while the 
