TAIL PUMPING BY THE BLACK PHOEBE

Black Phoebes (Sayornis nigricans) persistently pump their tails vertically while perched but the functional causes are unknown. I address four hypotheses about the function of this behavior in this species: (1) tail pumping aids in balance, (2) tail pumping enhances foraging, (3) tail pumping is a signal to territorial intruders, and (4) tail pumping is a signal to potential predators. The balance (mean +/- SE; unstable substrates: 0.23 +/- 0.024 pumps/sec, stable substrates: 0.22 +/- 0.019 pumps/sec), foraging (non-foraging individuals: 0.28 +/- 0.036 pumps/sec, foraging individuals: 0.20 +/- 0.026 pumps/sec) and intruder (pre-playback trial: 0.20 +/- 0.025 pumps/sec, House Finch [Carpodacus mexicanus] control trial: 0.26 +/- 0.029 pumps/sec. Black Phoebe experimental trial: 0.17 +/- 0.036 pumps/sec) hypotheses did not significantly explain tail pumping behavior. Tail pumping rates increased during predator sound playback (pre-playback trial: 0.23 +/- 0.009 pumps/sec, House Finch trial: 0.26 +/- 0.016 pumps/sec, Cooper's Hawk [Accipiter cooperii] trial: 0.61 +/- 0.013 pumps/sec, post-playback trial: 0.35 +/- 0.013 pumps/sec) and were accompanied by a high amount of both approaches (3.8 +/- 0.8) and calls (6.7 +/- 1.63). These results indicate that S. nigricans may be using tail pumping behavior as a pursuit-deterrent signal to advertise awareness to potential predators. Received 18 January 2011. Accepted 26 May 2011.