An Analysis of the Song-Flight of the Lapwing (Vanell Us Vanell Us L.) With Respect To Causation, Evolution and Adaptations To Signal Function

Abstract

AbstractThe song-flight of the lapwing was studied in order to find the main controlling factors, and explain the evolution and the adaptations to a signal function. The song-flight is made by males from the time the territories are founded until they become dissolved after the hatching of the eggs. The typical song-flight starts with the Butterfly Flight which is succeeded by one or several units, each consisting of the sequence: Alternating Flight - Low Flight- Ascent - High Flight - Vertical Dive - Alternating Flight. Each sequence of Ascent- High Flight - Vertical Dive is connected with a song phrase consisting of Motif 1, 2 and 3. The Alternating Flight is connected with dives of various types and the Humming Sounds produced by the wings. The song-flight is mainly internally controlled and can be regarded as a self-controlled behaviour sequence, which to some degree can be influenced by external factors. An internal rhythm gives rise to two or three activity maxima a day. The causal analysis suggests that the song-flight on the whole is aggressively motivated, the escape tendency playing a minor role. It consists of five phases. Phase 1 with the Butterfly Flight is sexually or aggressively dominated, phase 2 with the Alternating Flight, the dives, the Ascent and Motif 1 is dominated by aggression and has a shorter or longer interval interposed (the Low Flight), phase 3 with the High Flight and Motif 2 is a conflict behaviour dominated by the escape tendency and phase 4 with the Vertical Dive, Motif 3 and the Alternating Flight is dominated by an aggressive tendency. Finally phase 5, the landing, forms the conclusion. The results of the analysis implicate that the changes of motivation during the performance of the song-flight are internally controlled. The song-flight is a ritualized behaviour. As to most of its elements it is possible to deduce the origin on the basis of similarities in structure and regulating factors with other behaviour patterns of the species. The Butterfly Flight seems to originate from ordinary take off, while the Alternating Flight originates from more or less aggressively motivated behaviour like fast take off, chase flight and agitated flight, which normally occur as predator reactions and purely agonistic behaviour. Dives of Type 1 and 2 have evolved from an attack dive. The origin of the Low Flight is obscure. The Ascent may originate from the aggressive ascent to an air fight with other males. The origin of the High Flight is obscure. The Vertical Dive originates from an attack dive and the evolution has gone further than in the dives of the Alternating Flight. Motif 1 has evolved from an aggressively dominated sound occurring as a predator reaction and an agonistic behaviour, Motif 2 originates from a conflict-sound used as a predator reaction, whereas the origin of Motif 3 is obscure. For most of the song-flight elements it is possible to demonstrate different types of changes, which have taken place at the ritualization, and to demonstrate different kinds of adaptations to a signal function. The song-flight is adapted to its signal functions, i.e. being seen and heard distinctly over large distances in open terrain and announcing the place of territory, and it contains possibilities of transmitting several types of informations simultaneously.