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Titre :	Bottom line. Birds in a recreation area at the northern edge of the Alps
Auteurs :	Einhard Bezzel, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (53(3) MAR 2015)
Article en page(s) :	121-180
Résumé :	In 1980/83 and 2009/13 birds were counted along line transects in 114 1km-squares in the valleys and foothills of the Bavarian Alps around Garmisch-Partenkirchen. For all species in all months an overall loss of individuals of 36% was found. In 59 % of species the drift in abundance was negative, in 22% positive. Among 80 species each covering at least 0,1 % of the total of individuals, five increased by 100% or more, whilst in a further 29 the decrease was more than 50%. Comparisons with estimated population size in the surrounding area of 1440 km(2) before 1980 show that even large populations decreased considerably, and suggest that an overall decrease started only after the early eighties. In 1980/83 relatively more birds were concentrated in flocks of over 20 individuals than in 2009/13 (24% vs 14,2 %).Ranking negative drift of abundance within guilds, long distance migrants come first (17 negative, 0 positive among 19 species) before short-distance and partial migrants (16 negative, 4 positive among 23) and residents (11 negative, 9 positive among 27). High negative values in finches and thrushes may be due to seasonal food shortage. Birds which nest on the ground and/or in open areas are victims of increasing land use (agricultural grassland exploitation, sport fields, camping sites etc.). During winter the negative values of abundance drift are lower (in late winter occasionally even positive) than during the breeding season and shortly after, resulting in loss of species on small study plots during summer but not in winter.This may be explained by a decrease of productivity in the study area as well as in areas from which newly fledged birds regularly immigrate. Assumption of lower productivity is corroborated by a considerably higher decrease of successful broods (-0,71) compared to broods started (-0,54) and individuals during breeding season present (-0,29). In the seasonal pattern of change of abundance even in the commonest species the lowest values could be found during and shortly after breeding season (e.g. Great Tit, Blackbird). Long-term monitoring at a study plot at 811 m a. s. l. also reveals a decrease of successful broods during 1980-2009.Climate change may be responsible for the increasing numbers of partial migrants and residents in winter, also for the absence of northern winter visitors (e.g. Brambling, Redwing), and for a decrease of downward movements after snowfall at higher elevations (e.g. Ring Ouzel, Citril Finch, Water Pipit). In summer, the long-term local dynamics of species numbers and individuals at small plots correlated positively with regional development; in winter they did not. In winter, obviously occurrence and local traditions over years depend rather on individual experience and fate of birds than during summer.In altitudes up to 1000 m a.s.l. a shift of boundaries of breeding range or an increase of lowland birds in higher elevations could not be found because in most cases habitat degradation prevents the expected expansion of lowland birds into Alpine valleys. Only some residents and partial or short-distance migrants increased in the valleys (e.g. Magpie, Carrion Crow, Yellowhammer, Tree Sparrow, Woodpigeon).Long-term monitoring on smaller study plots revealed different traits of seasonal and annual dynamics even between species with similar life history (e.g. Coal and Crested Tit). In some cases (e. g. Crossbill) even two decades may be too short to explain long-term dynamics persuasively. Cases of dynamics deviating from rules or norms give supraregional relevance to detailed, thorough regional or local bird censuses alongside national or supranational monitoring schemes.

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