The phenomenon of synchronous take-offs in Gull-billed Terns. - E.V. Barbazyuk. - Berkut. 15 (1-2). 2006. - P. 159-175.
The phenomenon of synchronous takes-off displayed by Gull-billed Terns was studied during the pre-nesting period on Lakes Shalkar and Ayke, in southern Russia in 2000, 2003 and 2004. Synchronous take-offs of Gull-billed Terns are prominent phenomena observed during the pre-nesting period, and they could be considered as a component of pre-nesting aerial and ground behavior in this species. The intensity and dynamics of synchronous take-offs are influenced by a number of factors, among the more prominent ones being the time of the day, number of birds and weather conditions. The maximum number of synchronous take-offs was recorded in the morning and evening hours when the most birds were present at the gathering and roosting site. With the arrival of new parties of birds to the site the number of synchronous upflights increases, then reaches the maximum and stops rising when the mean number of birds is approximately 70 individuals per hour. The high intensity of synchronous take-offs is thought to be attributed to the abrupt change in the bird number per time unit, which occurs in the evening particularly from 1900 to 2030. Air temperature and wind speed also have impacts on the intensity of synchronous take-offs, especially at their extreme values: strong wind in conjunction with low temperatures lowers the intensity of synchronous take-offs and vice versa. Synchronous take-offs are strongly suspected to be an adaptive mechanism permitting synchronous egg-laying and thus reducing overall duration of maximal reproductive stages, which is very important when nesting in unstable habitats. [English].
Key words: Gull-billed Tern, Gelochelidon nilotica, behavior, courtship display, number of birds.
Address: Laboratory of Biocenological Processes, Institute of Plant and Animal Ecology, 8-Marta St., 202, Ekaterinburg, 620144, Russia; e-mail: bev@mail.esoo.ru.

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