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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Spotted Flycatcher Muscicapa striata in forests: bark beetles, storm, and fire - evolution through catastrophe?
Auteurs :	Wulf Gatter, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (136(1) 2016)
Article en page(s) :	53-68
Résumé :	In the course of decades of forest avifauna study, catastrophic storms in spruce forests of southwest Germany have led to surprising discoveries regarding Spotted Flycatchers, suggesting that the species has evolved adaptations to such natural disasters.In central Baden-Wurttemberg, Spotted Flycatchers are sparse, inconspicuous inhabitants of older forests. Severe storms in 1967, and especially in 1990 and 1999, provided the opportunity for a long-term study of the adaptation of this species to such events. The dynamics of unhindered succession caused by infestations of bark beetles (Scolytidae) allowed unexpected insights into the settlement strategy, diet phenology, and nesting and breeding behaviour of the flycatcher. The rise in numbers and/or settlement activity of Spotted Flycatcher triggered by the increase in the beetle population enabled us to study trophic processes in stocks of woodland, insects, and birds.In the absence of human influence, the scenario of these processes, where bark beetles from wind-thrown timber spread to and killed neighboring stands, could be followed for up to 16 years. High flycatcher population densities, as well as a band-like distribution that moved with the advancing infestation front, were found. The bark beetles supplied not only a surplus of food, but also of nest sites (thousands of 'bark-pockets, i.e. fragments caught in branch whorls by the Scolytidae beetles loosening the bark in spruce forests), a situation unknown in conventionally managed forests but probably normal in pristine forests. There were over a hundred dying trees standing in every flycatcher territory with a large number of such nesting possibilities, too many for predators to deal with. So we were able to observe the development by Spotted Flycatchers of flexible settlement and reproduction strategies.Territory occupation mostly in June could be interpreted as late arrival of the flycatchers from Africa or as an adaptation to bark beetle phenology. A third strategy could be that breeding outside the early part of the season, when predators are occupying their territories, allows the flycatchers to exploit the situation by breeding when the spatial and temporal pressures of competition and predation are already declining.The strong differences in biology between the Spotted Flycatcher and two Ficedula species (Pied and Collared Flycatcher) could indicate that the evolution of the species as a niche-nester has been shaped by the frequency of (large-scale) catastrophes occurring in unmanaged forest, especially since its wing morphology gives the species a high degree of mobility.The possibility of a 'pheno- or ecotype' Forest Spotted Flycatcher, adapted via mobility to the spatially and temporally unpredictable catastrophes of pristine forest is discussed and contrasted with urban Spotted Flycatchers.

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