. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Evolution of Ground Tyrants • Smith and VuiUeumier 251 jerking slightly back with each call. As the series accelerates the frequency of the last few units ascends and the bird climbs sharply into a stall. Just before stalling, the tail flicks up, then drops straight down- ward and spreads. The bird comes to hang vertically in the air, dangling its legs and feet. Its wings stretch over its back and nearly touch together as it utters the clear "whee-oo" and then pitches forward. Re- gaining speed, it retracts
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Evolution of Ground Tyrants • Smith and VuiUeumier 251 jerking slightly back with each call. As the series accelerates the frequency of the last few units ascends and the bird climbs sharply into a stall. Just before stalling, the tail flicks up, then drops straight down- ward and spreads. The bird comes to hang vertically in the air, dangling its legs and feet. Its wings stretch over its back and nearly touch together as it utters the clear "whee-oo" and then pitches forward. Re- gaining speed, it retracts its legs and flut- ters on in another performance. The flight is straight or twisted, and in the latter cases remains over a small piece of ground. After from one to about fifteen (commonly about five) stalls, the bird flies back to the slope or partly closes its wings, slightly cocks its tail, and dives to the ground. Peters (1923) gave an accurate but much less detailed description. There are various less complex forms. Just the terminal "whee-oo" may be uttered, which is very like counterparts of the dis- play known in M. albilora and M. rufi- vertex. At least in Ecuador in 1966, this was the common form after extensive predawn usage of the full form. Flights were then usually given in response to the passage overhead of an avian predator or in response to Aerial Display by a neighbor. The latter individual might be close to a boundary and the two displaying against one another, or (more commonly) might be responding to an avian predator—the first Mnscisaxicolo to go into Aerial Dis- play when a Sparrow Hawk or Buteo passed seemed to precipitate the display from most of his neighbors. Sometimes a bird calling "tek" would launch into Aerial Display without an introductory series. More commonly, a series of "tk" calls was uttered before the bird took flight—these may have replaced the usual aerial calls. Sometimes such a "tk" serie
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Keywords: ., bookauthorharvarduniversity, bookcentury1900, booksubjectzoology
