Vargas-Castro et a!. • SONG OF THE CLAY-COLORED THRUSH 
447 
Male B 
a a 
b 
b 
h H\i mi 
- f /it 
p* V* 
V'« v* 
i 2 
3 
4 
5 
6 
7 
Male D 
V 
/ 
r 
\ 
Mi 
c 
* 
N 
---1---1- 
1 2 
3 
4 
5 
6 
7 
Male F 
✓ 
6 i 2 
3 
4 
5 
6 
7 
> 
o 
c 
0 
3 
cr 
0 
5 
4 
3 
2 
1 
0 
Time (sec) 
FIG. 1. Spectrograms of the songs of three male Clay-colored Thrushes recorded during 2008 in San Jose, Costa Rica. 
Each of these songs is composed of 10 syllables in total, but males may sing songs ranging from one syllable to more than a 
hundred syllables. Songs with equal number of syllables usually vary in syllable sequence. The songs of male B, D, and F 
have 8, 9, and 10 different syllable types, respectively. Lower case letters a. b. and c indicate syllables of the same types. 
Syllables are 0.29 ± 0.07 sec in length arid separated by comparable silent intervals of 0.28 ± 0.07 sec in length (mean ± 
SD. a = 8 males, 54-125 syllables from 10 random songs/male were measured). Syllables have a sound frequency range of 
1100 to 5400 Hi and complex frequency modulations that may include buzzes or trills. 
USA) to produce .wav sound files. We used 
Raven Pro 1.4 software (Cornell Laboratory of 
Ornithology. Ithaca. NY. USA) for sound spec¬ 
trogram production and analysis. 
Song Measurements .—Each song is composed 
of a sequence of syllables, which are the minimal 
structural units of a song (Fig. I). Some syllables 
are single notes that appear as a eonlinous trace in 
the spectrogram, but other syllables tire comprised 
of multiple notes. Consecutive songs in a song 
bout are separated by silent intervals >1 sec. We 
measured the number of syllables per song, song 
duration, inter-song silent intervals, and song 
tempo (number of syllables/sec) in 695 songs 
(range: 44-150 songs/male). We randomly select¬ 
ed 10 songs from each male to measure syllable 
duration and inter-syllable silent intervals. 
The song of the Clay-colored Thrush, as in 
other thrushes, contains two syllable categories: 
whistles (or loud syllables) and soft syllables. The 
latter in other thrushes have been termed ‘hisselly’ 
or 'whisper' elements (Grabowski 1979, Rasmus¬ 
sen and Dabelsteen 2002. Johnson 2006). Soft 
syllables are sung at a lower amplitude and have a 
more complex structure than whistles. A given 
male Clay-colored Thrush sings at least two times 
as many soft syllable types as whistle syllable 
types (LEV. unpubl. data). Soft song in other 
songbird species is used in close-range commu¬ 
nication, primarily during aggressive interactions, 
courtship displays, or both, depending upon the 
species (Dabelsteen et al. 1998. Searcy and 
Beecher 2009). However, soft syllables are rare 
in the spontaneous 'loud' songs that we analyzed 
here. We recorded a total of 5.188 syllables of 
w hich 5,032 were whistles and only 3% were soft 
syllables. Thus, we included soft syllables in the 
song-level measurements but we excluded them 
from the syllable repertoire size estimation and 
syllable sharing analysis. 
