Avellis • TAIL-PUMPING BEHAVIOR OF THE BLACK PHOEBE 
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FIG. 2. (A) The highest proportion of Black Phoebes approaching the sound source was in the 'intruder trial, and (B) 
tail pumping rate was significantly lower when a recorded Black Phoebe was used in the playback trial. Different letters 
above error bars denote a significant difference by the Tukey post-hoc test. 
Signal to Territorial Intruders Hypothesis. —No 
individuals produced a call when this hypothesis 
was tested. There was a difference in whether an 
individual approached the hidden speaker among 
all playback trials (G : = 24.27. df = 3, P < 
0.001; Fig. 2A) and, after the interaction between 
playback type and individual was dropped from 
the analysis (F 4i27 = 0.77, P = 0.71) in tail 
pumping rates among playback types (F 3.39 = 
18.72, P < 0.001; Fig. 2B). The highest propor¬ 
tion of approaches and lowest tail pumping rates 
were observed when a conspecific vocalization 
was played. 
Site Impact.— Tail pumping rates were signif¬ 
icantly different among sites (Fig. 3), whereas 
individuals and individuals within sites were not 
different. Black Phoebes at ‘Lizard Rock’ had the 
greatest tail pumping rates. 
Signal to Predators Hypothesis.— There were 
differences in the amount of calls (G : = 20.61, <11 
~ P < 0.001) and approaches (O'* = 20.12, dt 
= 3 *P < 0.001) among playback types (Fig. 4). a 
positive correlation between the number ol calls 
Jn d approaches (r = 0.63. P < 0.001). and a 
difference in tail pumping rates among playback 
types (F 3i39 = 175.1. P < 0.001: Fig. 4) after the 
'Meraction of playback type and individual was 
dropped from the analysis (F 4[2 7 — 0.93, P = 
^•27). Approaches, calls, and tail pumping rates 
were greatest when the Coopers Hawk vocaliza¬ 
tion was played. 
DISCUSSION 
Balance Hypothesis.— Black Phoebes did not 
Pomp their tails to maintain balance, which has 
ken demonstrated in a variety of avian species. 
Bearded Reedlings ( Panurus biarmicus) with 
experimentally manipulated tail lengths did not 
differ in their ability to balance on unstable 
substrates when compared to controls (Romero- 
Pujante et al. 2005). Carder and Rjtchison (2009) 
found similar tail pumping rates for Eastern 
Phoebes on different substrate types (stable vs. 
non-stable) and 00 correlation between tail 
movements and wind velocity. Tail pumping 
occurs in only a small percent of perching birds 
(Carder and Ritchison 2009) and is probably not 
used to maintain balance. 
Foraging' Enhancement Hypothesis .—Tail pump¬ 
ing did not predict foraging behavior of Black 
Phoebes. However, of those birds that did forage, 
successful bouts declined as tail pumping increased. 
Similarly, Eastern Phoebes (Carder and Ritchison 
2009) and White Wagtails (Motacilla alba) (Rand¬ 
ier 2006) did not move their tails more often when 
foraging. Randier (2006) found a negative relation¬ 
ship between tail movement and foraging rates, and 
a positive relationship between tail movements and 
Site 
FIG. 3. Tail pumping rates of Black Phoebes signifi¬ 
cantly differed among sites. A* indicates a marginal 
difference (P = 0.08) via the Tukey post-hoc test. 
