Huge memory in a tiny brain: unique organization in the advertising song of Pallas's Warbler Phylloscopus proregulus

Abstract

The song structure of Pallas's Warblers – one of the smallest birds in the Palaearctic fauna – was investigated in central-southern Siberia (Russia). The endless song of this species consists mainly of various trills replacing each other in rapid succession. The individual repertoires include up to 270 types of trills and other vocal components grouped into packages – specific vocal structures repeating on a regular basis during the course of singing. Duration of the packages ranges from 9.9 up to 68.6 s (on average 30.5 ± 12.6 s). Each package contains a unique set of mutually associated vocal components. All components are typical for the given package and are usually not found in the other packages from a particular male. All packages are of a highly combinatory nature. The succession order of the different components within a given package varies over the course of its performance. The individual repertoire includes up to 20 different packages, which are organized serially in accordance with several (3–6) programs providing a highly fixed sequence of their performance. The overall duration of such programs ranges from 25 to 275 s (on average 101.3 ± 60.2 s). One program contains from 2 to 11 (median 3) packages. Their sequence one after another remains absolutely constant in the repeated performances even in the longest programs. Some features of the vocal memory in song birds are discussed with the unique organization of the songs of Pallas's Warblers as an example.