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Vagrancy in Birds

By Alexander Lees and James Gilroy

Helm, 2021

Hbk, 400pp; 360 colour photographs and illustrations

ISBN 978-1-4729-6478-6; £39.99

There are a lot of people out there, maybe some of them reading this, who believe that vagrant birds get too much attention. Many people don’t understand the community within the hobby that makes a priority of finding and seeing rare birds – birds which are, so they say, genetically ‘dead’, lost to the population and of no further interest. They might think this book isn’t for them, but frankly, they’d be wrong.

This book makes the case that vagrancy in birds matters. Even if you can’t buy into the enjoyment of seeing an extralimital individual that may be struggling through its last few days of life, the introductory sections of the book firmly establish that in order to understand vagrancy, we need to understand some biological problems that are of interest to all birders and ornithologists. The first 70 pages outline these issues – how do birds know where they are in the world?; what compels them to move off to a different part of the world?; and what cues do they use to get there? It comes down to what birds see and sense: the magnetic field of the earth, the patterns of the stars, the position of the sun, polarisation of the sky, and the topography and smells of the earth. The book describes how birds use these abilities to navigate, and how this feeds into the things that can go awry – what can send them the wrong way; what, if anything, a bird can do to rectify an error; and at which point the bird gives up and goes with the wind. The authors cover what, to many readers, will be conceptually familiar ground – reverse, drift, and mirror-image migration (things that have been covered many times previously) – but their discussion is always rooted in a firm understanding of biology and with an eye to the consequences of vagrancy for the birds involved and for the ecosystems in which they live.

The bulk of the book is an analysis of known vagrancy events in every family of birds, starting with the Struthionidae (ostriches) and working methodically through to the Thraupidae (tanagers). Although that means there are a large number of families for which the summary is basically ‘sedentary with no known vagrancy’, there are many families prone to vagrancy that get several pages of detailed description and analysis. The geographical coverage is worldwide and well balanced.

The ability of birds to respond to their environment is fundamental to our understanding of the consequences of climate change. Vagrancy events may lead to the development of new migration routes and the exploration of potentially favourable habitats. This book makes that clear. It’s a shame it was finished too soon to include the 2021 paper from Paul Dufour and colleagues (Current Biology 31: 5590–5596), which demonstrated that Richard’s Pipits Anthus richardi are now migrating regularly from their breeding grounds to southern Europe and back again – a new migration route quite possibly made advantageous by changing climate. 

This is an important and hugely entertaining book that represents an enormous amount of research and is a valuable resource to read through or dip into.

Martin Collinson

Issue 4
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