been possible to determine the phylogeny, assess differentiation within and
between regions and show evidence for bottlenecks and rapid expansion (Ödeen
and Björklund 2003).
Human genetic studies have increasingly used single nucleotide polymor-
phisms (SNPs), which determine single base differences at a range of locations
across the genome. This technique has recently been applied to birds (Primmer
et al. 2002). These have a number of advantages such that they occur at a high
frequency across the genome and this multilocus approach probably gives more
reliable results than just comparing one sequence. Another advantage is that
SNPs can be analyzed using automated processes.
Sex determination. A high proportion of bird species are sexually monomorphic
and are therefore difficult or impossible to sex, except by laparotomy to examine
the gonads. Nestlings or embryos are obviously difficult to sex. A DNA test that
can be used to establish the sex of most species of birds (Griffiths et al. 1998) is
based on two conserved chromo-helicase-DNA-binding (CHD) genes that are
located on the sex chromosomes. Unlike mammals, in birds the females are
heterozygous (ZW) and males are homozygous (ZZ). The CHD-Wgene is locat-
ed on the W chromosome and is therefore unique to females. CHD-Zis on the
Z chromosome and therefore occurs in both sexes. The test involves PCR with a
single set of primers. It amplifies homologous sections of both genes which incor-
porate introns whose lengths usually differ. When examined on a gel, there is a
single band in males (CHD-Z) but in females there is a distinct second band
(CHD-W). Sexing can be done for nestlings and even embryos, but may be unre-
liable in eggs that have not yet developed a visible embryo (Kalmbach et al. 2001).
Prey species. Another potential use of molecular techniques is to identify prey
species in the gut contents, feces or regurgitated pellets of predator species
(Symondson 2002). This is carried out by amplification of the prey DNA using
PCR and then comparing sequences with online DNA databases of previously
studied genes.
Acknowledgements
George Bentley, Tony Williams, Shelley Hinsley, Bengt Silverin, Sara Goodacre,
and Brent Emerson provided useful information for this chapter.
References
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Bekoff, M. (1993). Experimentally induced infanticide: the removal of birds and its
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