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Intl. J. of Super Species Research 2012, Vol.2, No.1, 1
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http://ijssr.sophiapublisher.com
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Table 2 Correlations of mite abundance to different measures of body condition
Species
Correlation
Spearman’s ρ
N
P value
Mites and muscle
0.101
35
0.563
Mites and fats
0.790
35
0.274
Blackcap
Mites and weight
0.296
35
0.085*
Mites and muscle
-0.144
10
0.692
Mites and fats
0.529
10
0.116
House sparrow
Mites and weight
0.215
10
0.550
Mites and muscle
-0.333
14
0.245
Mites and fats
0.779
14
<0.001**
Sardinian waebler
Mites and weight
0.332
14
0.246
Mites and muscle
-0.082
13
0.791
Mites and fats
-0.29
13
0.337
Willow warbler
Mites and weight
0.12
13
0.697
Note: *Marginally insignificant; ** Very significant
Proctor and Owens, 2000). Species characterised by
both low prevalence and low mite numbers tend to be
solitary species (e.g. robins, Sardininan warblers,
Bonelli’s warblers, woodchat shrikes), often occurring
in pairs and highly territorial, with little or no contact
to conspecifics. Although few birds were captured to
carry out meaningful analysis, these trends concur
with previous findings by Poulin (1991), who found a
positive relationship between mite abundances and
host gregariousness.
Blackcaps, which were among the most heavily
infested species (100% prevalence, average 72.5 mites
per wing), appear to be an exception to the trendas
they tend to be relatively solitary, feeding and
breeding in pairs and defending their territories
against conspecifics. As suggested by Fowler and
Hodson (1991), migratory birds such as blackcaps
could potentially be carrying different mite species,
collected enroute during migration.
4.1 Mite abundance in relation to sex and age
Various authors have suggested that mite abundances
can be related to sex (Hamstra and Badyaev, 2008;
Blanco and Frias, 2001; Blanco et al., 1999), mostly
as a result of variations in hormone levels between
different sexes (Blanco et al., 1999). Concurring with
the findings from Galvan and Sanz (2006), Blanco et
al (1997) and many others, the results of this study
failed to find such associations for any of the species,
indicating that the proposed variations in hormonal levels
may not be strong enough to explain differences in mite
abundances. While this may in part be due to the low
number of captured birds, it is more likely that both
sexes do indeed harbour similar abundances of mites.
Similarly, the results suggest no differences between
mite abundances between juvenile and adult birds.
Several studies found age to be important factor in
determining mite abundances on birds, with mite
loads usually increasing with increasing age (Hamstra
and Badyaev, 2008; Blanco and Frias, 2001),
attributed to the fact that mites are generally
transferred from the female to the fledglings in the
nest and then increase with reproduction and sociality
over time (Galvan and Sanz, 2006; Figuerola, 2000;
Poulin, 1991). As this study was carried out just prior
to the breeding season, any effect of age may have
been masked by the fact that juveniles have been
exposed to infested adults throughout winter (high
winter sociality) as suggested by McClure (1989).
4.2 Mite infestation and host body condition
The various scores of body condition used by this
study were poor predictors of mite abundances. For
the four species that were studied in more detail, only
Sardinian warblers seemed to be characterized by a
significant relationship between fat scores and mite
loads (p<0.001), while the relationship between
weight and feather mite load in blackcaps was
marginally non-significant (p=0.085). The fact that
both of these relationships were positive (as body
condition improved, mite abundances increased)
indicates that mites may not be detrimental to their
hosts, contrary to what has been suggested by many