4.3.2.5 — Aves: Songbirds — Passeriformes

The songbirds are the largest group of around 4300 species from 30 families. At present, 592 migrants have been identified, using data from K. Boehning-Gaese (Boehning-Gaese 1998) for Palaearctic and North American migrants. For southern Asia, South East Asia and Australasia, the present selection was limited to threatened migratory songbirds. Therefore, it is still preliminary to present a summarising statistics of migrant precentage per family. The following section comments on those songbirds covered by CMS, and some additional threatened species in urgent need of conservation measures.

With 1423 species, the flycatchers (Muscicapidae) are by far the largest songbird family. At present, 115 migratory flycatchers have been identified (according to the GROMS criterion), and 100 species cross political boundaries during migration. Because the entire family is listed on Appendix II, this status could be attributed individually to 100 migratory flycatchers.⁴¹ Therefore, the GROMS contains a first list of CMS Appendix II on a species basis. The threatened aquatic warbler (Acrocephalus paludicola) is red-listed as "Vulnerable", due to its serious decline in the last decades and included within CMS Appendix I (for details, see Figure A2.48). This species is a marshland specialist, and it hopefully profits from measures for wetland conservation and implementation of the European Action Plan (Heredia et al. 1996).

Several other threatened songbirds from distinct families are listed on Appendix I, which are discussed in further details within the map figure captions: the blue swallow (Hirundo atrocaerulea – Hirundinidae, Figure A2.70), Kirtland’s warbler (Dendroica kirtlandii – Parulidae, Figure A2.71), the strange-tailed tyrant (Alectrurus risora –Tyrannidae, Figure A2.72), three species of Sporophila spp. (Emberizidae: Figures A2.73, A2.74), and the saffron-cowled blackbird (Agelaius flavus – Icteridae: Figure A2.74). Ten additional migratory songbirds are listed as "Endangered" or "Vulnerable" by the
International Red List 2000. All cross national boundaries during migration, and therefore qualify for CMS listing due to their unfavourable conservation status (Table 4.8).

Long-term studies of songbird populations reveal a decline of long-distance migrants, while several resident species or short-distance migrants are increasing (Bauer & Berthold> 1997, Berthold> et al. 1998, Gatter 2000). The reasons are complex, and differ between regions. In North America, the disappearance of long-distance migrants became evident in the 1970s, and "the mystery of the missing songbirds" was analysed comprehensively by Terborgh (1989). He showed convincingly that many of the forest-dwelling species suffered from loss of forest habitat in their tropical wintering grounds. A second, more recent wave of decline is due to changes in coffee plantation schemes, where shade cultures with tropical trees are substituted by more intensive coffee monocultures (Tangley> 1996). In addition, clear-cutting of forests in the northern breeding ranges affects Neotropical migrants. Some species are particularly sensitive, such as Swainson’s thrush (Catharus ustulatus – CMS Appendix II), which declined even after low-intensity disturbance by small-patch logging (Chambers> et al. 1999).

The ecological situation for long-distance migrants between Africa and Eurasia is quite different, but equally serious. There are less forest specialists than in the Americas. Declines have been attributed to pesticide use and sever droughts in the Sahel area, affecting important staging areas for trans-Saharan migrants (Berthold 2000). But the same author resumes for the decline of songbirds: "Die Ursachen für ihren Rückgang scheinen z.T. ähnlich komplex zu sein wie beim Weißstorch und sind bisher leider für keine Art vollständig aufgeklärt." ("The reasons for their decline appear in some ways to be as complex as in the case of the white stork, and are unfortunately not fully known for any species") (l.c. p. 211). The importance of habitat quality in the European breeding area was demonstrated by a 15-year study by Tomialojc & Weselowski (1994), who demonstrated stability of a bird community inhabiting the Polish primary forest area in Bialowieza.

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede