Working for birds in Africa

The Reed Warblers. Diversity in a Uniform Bird Family.

Wed, 02/06/2013 - 11:23 -- abc_admin
Bernd Leisler and Karl Schulze-Hagen (translated by Brian Hillcoat), illustrated by David Quinn, 2011. Utrecht: KNNV Publishing in association with Max Planck Institute for Ornithology. 327 pp, many photographs and maps. Hardback. ISBN 978-90-5011-3915.
237-238

The reed warblers of the title refer to the recently defined family of Acrocephalidae, which comprises about 53 species in six genera, including Acrocephalus, Hippolais, Nesillas (Madagascar) and Iduna (four of the ‘Olivaceous’ group ex-Hippolais, and two of the Chloropeta yellow warblers of Africa). These ‘plain’ warblers are found on all continents except the New World, as well as many remote oceanic islands and present an extraordinary variety of life strategies and adaptations to their environment. The authors offer a remarkable
synthesis and analysis of their own field work and of research by numerous others in the last 50 years, supported by a bibliography of over 1,000 titles. Fifteen chapters cover the fields of systematics, foraging and habitat use, ecomorphology, mating systems and reproduction, intra- and interspecific competition, migration, song, cuckoo parasitism, island species and conservation issues, as well as the eco-ethological convergence observed in New World marsh-dwellers.

What made reed warblers so popular with researchers (accessibility of low nests, high breeding densities) also made them very popular with cuckoos, and Eurasian species are by far the most frequent hosts of Common Cuckoo Cuculus canorus. The comparison of the different defence strategies of small and large reed warblers makes fascinating reading: Great Reed Warblers Acrocephalus arundinaceus are better able physically to remove a cuckoo’s egg from the nest, whereas smaller Marsh Warblers A. palustris avoid the problem by simply puncturing the unwanted egg with the bill, and Eurasian Reed Warblers A. scirpaceus (with their weaker bill) mainly by deserting; Marsh Warblers are also much more successful than their congeners at rejecting cuckoo eggs, which must be related to their shorter breeding seasons and reduced chances of relaying.

Mating systems vary from monogamy with life-long pair-bonding where food is scarce (in island species), to promiscuity with no male parental care in food rich habitats (Aquatic Warbler A. paludicola). The long-term study of the cooperative breeding system of the Seychelles Warbler A. sechellensis by Jan Komdeur and collaborators is a model of scientific methodology. A combination of detailed monitoring of known colour-ringed birds, careful planning of translocation of certain individuals to unoccupied islands (which also saved the species from extinction) and sophisticated genetic technology have led to the complicated mechanisms of this system being unravelled, including the discovery that breeding females are able to control the sex of their offspring, by laying ‘female’ eggs when they need helping daughters!

Some of the Acrocephalus warblers are among the world’s best vocal mimics. I was interested to read that the authors interpret the extreme complexity of vocal repertoires as a side-effect of song learning rather than as an adaptation. In support, they cite a study of Black-browed Reed Warbler A. bistrigiceps showing that females do not at all prefer males with larger mimetic repertoires; this is the same conclusion I reached concerning the highly mimetic songs of Marsh Warbler more than 30 years ago. They could also have mentioned the intriguing vocal play of Marsh Warblers peacefully countersinging with their neighbours during the incubation period, only when favourable weather allows them ‘time off’ from looking for food (Le Gerfaut 69: 475–502).

The chapter on conservation and population trends naturally devotes a large section to our most threatened European species, Aquatic Warbler; it also stresses the ever-increasing effect of climate change with (for instance) the spectacular loss of range of Icterine Warbler Hippolais icterina in Western Europe to the benefit of the expansion of range by the Melodious Warbler H. polyglotta. Long-distance migrants like Icterines cannot adapt to the ever-earlier peak in insect abundance and are among the climate change losers. The story of how reed warblers colonised Pacific islands (and eventually Australia!), based on genetic research by Alice Cibois and co-workers, also makes exciting reading.

I hope that these few examples are sufficient to convince everyone that this book should be read by not just warbler enthusiasts, but by all naturalists and students of behavioural and molecular ecology. The authors write with an evident love of their subjects, the text is both scholarly and a pleasure to read, and the whole is beautifully produced and illustrated. With few exceptions only English names of animal and plant species are used, and it is useful to learn (p. 327) that full names can be found in an appendix on the publishers’ website.

 

Françoise Dowsett-Lemaire

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