give a poor indication of gut parasite load. Blood parasite assessment requires
blood biopsy (see below and Chapter 10).
4.9 Biopsy
Recent developments allow more precise measurements of condition, metabolic
rate, and life history to be made, from blood and feather samples, than have ever
previously been possible. The technical details need not concern us here (see
Chapter 9) but a short list may be helpful. In some countries special legislation
may apply to these procedures (e.g. ASPA in the United Kingdom) so a specific
licence may be required. From small blood samples, typically taken by venipunc-
ture of the ulnar wing vein (Hawkins et al. 2001), genetic, condition, and stress
analyses (fat, protein, and corticosterone) can be undertaken (Brown 1996). It is
well established that such sampling does not cause lasting harm to the birds
(Stangel 1986). The ratio of isotopes (e.g. of Carbon and Hydrogen) in feather
keratins can be measured from small feather samples, and these can be used (with
caution because C isotopes can also vary with diet and habitat) to determine,
within broad regional limits, where the bird molted because these ratios differ
geographically (Hobson 1999; Bearhop et al. 2000; Wassenaar and Hobson
2000). If the bird can be trapped and retrapped within a short time (e.g. 36 h),
a small injection of doubly-labelled water can be used to assess metabolic rate,
which is reflected in the rate at which the ratio of labelled to unlabelled water
changes over time, after equilibration (Tatner and Bryant 1986; Bryant 1997).
Feces for analysis (Chapter 10) can easily be collected during handling, with
the advantage that details of the individual will be known. Finally, for further
observations that can be made of trapped migrants, such as preferred migratory
orientation (e.g. Busse 1995), see Chapter 7.
Acknowledgements
I am indebted to Peter Kennerley, David Wells, Paul Leader, David Melville (all Far
East) Jeremy Lindsell (Africa), Jose Arevalo (South America), Paul Salaman (South
America), Leon Bennun/Colin Jackson (Africa and tropical ringing generally)
and Peter Potts for their advice on tropical issues, and to the editors for their
constructive comments on an earlier draft.
References
Baker, J.K. (1993). Identification Guide to European Non-Passerines. BTO Guide 24, Thetford.
Bearhop, S., Phillips, R.A., Thompson, D.R., Waldron, S., and Furness, R.W. (2000).
Variability in mercury concentrations of great skuas Catharacta skua: the influence of
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