Fróðskaparrit - 01.01.2002, Blaðsíða 141

VISTFRØÐIN HJÁ INNVORTIS SNÍKUM í LUNDA
139
ductive stages of the birds’ lives. In migrat-
ing birds, females typically have longer na-
tal dispersal than males. (Møller and
Erritzøe, 2001). The hypothesis is that the
development of the immune system is pos-
itively correlated with the diversity of the
parasitic fauna to which the host is ex-
posed, which is again positively correlated
to the dispersal distance of the host (Møller
and Erritzøe, 2001). Further investigations
are necessary to explore this hypothesis, es-
pecially as knowledge is sparse about the
migration behaviour of pre-mature puffins.
Hoberg (1987); Bakke (1972); and
Bockeler and Vauk-Hentzelt (1979) report-
ed sludies on a total of 265 birds; a total of
8 females and 7 males were infested with
pentastomes. Whilst the present study ap-
pears to show a tendency for females being
the more heavily infested with pentas-
tomes, this is not supported by the litera-
ture.
Host age
The reason for adult birds tending to have a
higher relative intensity of infestation with
trematodes may reflect immunological
suppression at a cost to reproductive effort,
a phenomenon that may impose not only
immediate effects but also possibly life-
long negative consequences for viability
(Nordling et al., 1998). An alternative or
complementary cause might lie in the dif-
ferences in the functional response of the
immune system, in which information on
immune responses is stored in memory
cells in adult birds, rather than in the func-
tion of the Bursa Fabricii in juvenile birds
(Møller and Erritzøe, 2001), the functional
response of the adult being less efficient
perhaps.
Regarding pentastomes, other investiga-
tors (Bakke, 1972; Bðckeler and Vauk-
Hentzelt, 1979; Bockeler, 1984) have
shown a higher prevalence of infestation in
juvenile than in adult birds; the converse
was found in the present study, in which all
pentastome-infested birds were adults.
Seasonal effects
The helminth fauna of migrating birds is
generally seasonal, a natural consequence
of seasonal and regional fiuctuations in
food supply (Bykhovskaya-Pavlovskaya,
1953; 1962; Bezubik, 1956; Jarecka, 1958;
Polozhentsev and Negrobov, 1958; Kassi-
mov et al., 1962; Rysavy, 1962; 1964 in
Wallace and Pence, 1986). A lack of re-
placement might also be an influence,
when prey species change in connection
with migration, and longevity of the para-
sites is limited (Avery, 1969). The helminth
fauna of auks is also seasonal and related to
the breeding areas (Hoberg, 1981), as there
is a seasonal occurrence of pentastomes
(Bockeler, 1984). Parasites usually adapt
their reproductive period to the annual cy-
cle of the host, with parasite population
densities peaking late during the hosts’ re-
productive season (Cox, 1993). Such peaks
may be in part at least to a consequence of
the immunological cost of reproduction
during the breeding season (Nordling,
1998). In addition, the risk of infestation is
usually density-dependent (Begon et ai,
1986), and the puffin density is clearly
highest in the breeding period. The great
dispersion of the birds outside the breeding